| Message ID | 1456770820-21341-4-git-send-email-adhemerval.zanella@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 29/02/16 18:33, Adhemerval Zanella wrote: > This patch implements a new posix_spawn{p} implementation for Linux. The main > difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK > flags and a direct allocated stack. The new stack and start function solves > most the vfork limitation (possible parent clobber due stack spilling). The > remaning issue are related to signal handling: > > 1. That no signal handlers must run in child context, to avoid corrupt > parent's state. > 2. Child must synchronize with parent to enforce stack deallocation and > to possible return execv issues. > > The first one is solved by blocking all signals in child, even NPTL-internal > ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation > in parent and a synchronization with using a pipe or waitpid (in case or error). > The pipe has the advantage of allowing the child signal an exec error (checked > with new tst-spawn2 test). > > There is an inherent race condition in pipe2 usage for architectures that do not > support the syscall directly. In such cases the a pipe plus fctnl is used > instead and it may lead to file descriptor leak in parent (as decribed by fcntl > documentation). > > The child process stack is allocate with a mmap with MAP_STACK flag using > default architecture stack size. Although it is slower than use a stack buffer > from parent, it allows some slack for the compatibility code to run scripts > with no shebang (which may use a buffer with size depending of argument list > count). > > Performance should be similar to the vfork default posix implementation and > way faster than fork path (vfork on mostly linux ports are basically > clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls > required for the stack allocation/deallocation. > > It fixes BZ#10354, BZ#14750, and BZ#18433. > > Tested on i386, x86_64, powerpc64le, and aarch64. > on aarch64 this caused FAIL: nptl/tst-exec1 with error msg "join in thread in parent returned!?" i think the cause is that glibc clone sets tcb.tid = tcb.pid = -1 if CLONE_VM|CLONE_VFORK is used, which means the vfork child clobbers the parent tcb.tid. (and pthread_join tests tcb.tid and thus fails in tst-exec1.) i believe all targets are affected.
On 12-04-2016 15:06, Szabolcs Nagy wrote: > On 29/02/16 18:33, Adhemerval Zanella wrote: >> This patch implements a new posix_spawn{p} implementation for Linux. The main >> difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK >> flags and a direct allocated stack. The new stack and start function solves >> most the vfork limitation (possible parent clobber due stack spilling). The >> remaning issue are related to signal handling: >> >> 1. That no signal handlers must run in child context, to avoid corrupt >> parent's state. >> 2. Child must synchronize with parent to enforce stack deallocation and >> to possible return execv issues. >> >> The first one is solved by blocking all signals in child, even NPTL-internal >> ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation >> in parent and a synchronization with using a pipe or waitpid (in case or error). >> The pipe has the advantage of allowing the child signal an exec error (checked >> with new tst-spawn2 test). >> >> There is an inherent race condition in pipe2 usage for architectures that do not >> support the syscall directly. In such cases the a pipe plus fctnl is used >> instead and it may lead to file descriptor leak in parent (as decribed by fcntl >> documentation). >> >> The child process stack is allocate with a mmap with MAP_STACK flag using >> default architecture stack size. Although it is slower than use a stack buffer >> from parent, it allows some slack for the compatibility code to run scripts >> with no shebang (which may use a buffer with size depending of argument list >> count). >> >> Performance should be similar to the vfork default posix implementation and >> way faster than fork path (vfork on mostly linux ports are basically >> clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls >> required for the stack allocation/deallocation. >> >> It fixes BZ#10354, BZ#14750, and BZ#18433. >> >> Tested on i386, x86_64, powerpc64le, and aarch64. >> > > on aarch64 this caused > > FAIL: nptl/tst-exec1 > > with error msg "join in thread in parent returned!?" > > i think the cause is that glibc clone sets > tcb.tid = tcb.pid = -1 if CLONE_VM|CLONE_VFORK > is used, which means the vfork child clobbers > the parent tcb.tid. (and pthread_join tests > tcb.tid and thus fails in tst-exec1.) > i believe all targets are affected. I think the problem is glibc's vfork only changes the TCB's pid fields while fork changes both pid and tid in case on CLONE_VM. Now I am trying to found out why exactly this difference handling of internal fields...
On 12-04-2016 15:15, Adhemerval Zanella wrote: > > > On 12-04-2016 15:06, Szabolcs Nagy wrote: >> On 29/02/16 18:33, Adhemerval Zanella wrote: >>> This patch implements a new posix_spawn{p} implementation for Linux. The main >>> difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK >>> flags and a direct allocated stack. The new stack and start function solves >>> most the vfork limitation (possible parent clobber due stack spilling). The >>> remaning issue are related to signal handling: >>> >>> 1. That no signal handlers must run in child context, to avoid corrupt >>> parent's state. >>> 2. Child must synchronize with parent to enforce stack deallocation and >>> to possible return execv issues. >>> >>> The first one is solved by blocking all signals in child, even NPTL-internal >>> ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation >>> in parent and a synchronization with using a pipe or waitpid (in case or error). >>> The pipe has the advantage of allowing the child signal an exec error (checked >>> with new tst-spawn2 test). >>> >>> There is an inherent race condition in pipe2 usage for architectures that do not >>> support the syscall directly. In such cases the a pipe plus fctnl is used >>> instead and it may lead to file descriptor leak in parent (as decribed by fcntl >>> documentation). >>> >>> The child process stack is allocate with a mmap with MAP_STACK flag using >>> default architecture stack size. Although it is slower than use a stack buffer >>> from parent, it allows some slack for the compatibility code to run scripts >>> with no shebang (which may use a buffer with size depending of argument list >>> count). >>> >>> Performance should be similar to the vfork default posix implementation and >>> way faster than fork path (vfork on mostly linux ports are basically >>> clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls >>> required for the stack allocation/deallocation. >>> >>> It fixes BZ#10354, BZ#14750, and BZ#18433. >>> >>> Tested on i386, x86_64, powerpc64le, and aarch64. >>> >> >> on aarch64 this caused >> >> FAIL: nptl/tst-exec1 >> >> with error msg "join in thread in parent returned!?" >> >> i think the cause is that glibc clone sets >> tcb.tid = tcb.pid = -1 if CLONE_VM|CLONE_VFORK >> is used, which means the vfork child clobbers >> the parent tcb.tid. (and pthread_join tests >> tcb.tid and thus fails in tst-exec1.) >> i believe all targets are affected. > > I think the problem is glibc's vfork only changes the TCB's pid fields > while fork changes both pid and tid in case on CLONE_VM. Now I am trying > to found out why exactly this difference handling of internal fields... In fact I think clone.S should not reset the tid member in TCB for fork(CLONE_VM|...) and it is what vfork does internally. It is used on INVALID_TD_P and INVALID_NOT_TERMINATED_TD_P macros used on pthread_join and pthread_cancel. A value equal to -1 will issue an error for such case, which mean that if a multithread program issues a clone(CLONE_VM|...) from a posix_spawn, a subsequent pthread_join might fail due invalid tid value. And I think it is what is happening in your system on tst-exec1: although pthread_create is issue before posix_spawn, I think posix_spawn clone might be executing before the pthread_join in some cases leading to this issue. I will propose a patch to modify clone to not reset the tid value.
On 12-04-2016 17:20, Adhemerval Zanella wrote: > > > On 12-04-2016 15:15, Adhemerval Zanella wrote: >> >> >> On 12-04-2016 15:06, Szabolcs Nagy wrote: >>> On 29/02/16 18:33, Adhemerval Zanella wrote: >>>> This patch implements a new posix_spawn{p} implementation for Linux. The main >>>> difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK >>>> flags and a direct allocated stack. The new stack and start function solves >>>> most the vfork limitation (possible parent clobber due stack spilling). The >>>> remaning issue are related to signal handling: >>>> >>>> 1. That no signal handlers must run in child context, to avoid corrupt >>>> parent's state. >>>> 2. Child must synchronize with parent to enforce stack deallocation and >>>> to possible return execv issues. >>>> >>>> The first one is solved by blocking all signals in child, even NPTL-internal >>>> ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation >>>> in parent and a synchronization with using a pipe or waitpid (in case or error). >>>> The pipe has the advantage of allowing the child signal an exec error (checked >>>> with new tst-spawn2 test). >>>> >>>> There is an inherent race condition in pipe2 usage for architectures that do not >>>> support the syscall directly. In such cases the a pipe plus fctnl is used >>>> instead and it may lead to file descriptor leak in parent (as decribed by fcntl >>>> documentation). >>>> >>>> The child process stack is allocate with a mmap with MAP_STACK flag using >>>> default architecture stack size. Although it is slower than use a stack buffer >>>> from parent, it allows some slack for the compatibility code to run scripts >>>> with no shebang (which may use a buffer with size depending of argument list >>>> count). >>>> >>>> Performance should be similar to the vfork default posix implementation and >>>> way faster than fork path (vfork on mostly linux ports are basically >>>> clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls >>>> required for the stack allocation/deallocation. >>>> >>>> It fixes BZ#10354, BZ#14750, and BZ#18433. >>>> >>>> Tested on i386, x86_64, powerpc64le, and aarch64. >>>> >>> >>> on aarch64 this caused >>> >>> FAIL: nptl/tst-exec1 >>> >>> with error msg "join in thread in parent returned!?" >>> >>> i think the cause is that glibc clone sets >>> tcb.tid = tcb.pid = -1 if CLONE_VM|CLONE_VFORK >>> is used, which means the vfork child clobbers >>> the parent tcb.tid. (and pthread_join tests >>> tcb.tid and thus fails in tst-exec1.) >>> i believe all targets are affected. >> >> I think the problem is glibc's vfork only changes the TCB's pid fields >> while fork changes both pid and tid in case on CLONE_VM. Now I am trying >> to found out why exactly this difference handling of internal fields... > > In fact I think clone.S should not reset the tid member in TCB for > fork(CLONE_VM|...) and it is what vfork does internally. It is > used on INVALID_TD_P and INVALID_NOT_TERMINATED_TD_P macros used on > pthread_join and pthread_cancel. A value equal to -1 will issue > an error for such case, which mean that if a multithread program > issues a clone(CLONE_VM|...) from a posix_spawn, a subsequent > pthread_join might fail due invalid tid value. > > And I think it is what is happening in your system on tst-exec1: > although pthread_create is issue before posix_spawn, I think > posix_spawn clone might be executing before the pthread_join > in some cases leading to this issue. > > I will propose a patch to modify clone to not reset the tid value. > But I am not sure if we just should avoid touch any internal TCB headers if CLONE_VFORK is set, thoughts?
Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: > +static int > +__spawni_child (void *arguments) <snip> > +fail: > + /* Since sizeof errno < PIPE_BUF, the write is atomic. */ > + ret = -ret; > + if (ret) > + while (write_not_cancel (p, &ret, sizeof ret) < 0) > + continue; > + exit (SPAWN_ERROR); > +} Sorry for not noticing earlier, but shouldn't it be "_exit" instead of "exit" when the child fails? At least that's what CLONE_VFORK section of the clone(2) manpage documents, and what normal vfork requires. > +static int > +__spawnix (pid_t * pid, const char *file, And the comment in __spawnix mentions "_exit", too: > + /* The clone flags used will create a new child that will run in the same > + memory space (CLONE_VM) and the execution of calling thread will be > + suspend until the child calls execve or _exit. These condition as > + signal below either by pipe write (_exit with SPAWN_ERROR) or > + a successful execve. > + Also since the calling thread execution will be suspend, there is not > + need for CLONE_SETTLS. Although parent and child share the same TLS > + namespace, there will be no concurrent access for TLS variables (errno > + for instance). */ > + new_pid = CLONE (__spawni_child, STACK (stack, stack_size), stack_size, > + CLONE_VM | CLONE_VFORK | SIGCHLD, &args); Anyways thanks for implementing this so I can look forward to using this faster version :)
On 05/29/2016 11:54 AM, Eric Wong wrote: > Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: >> +static int >> +__spawni_child (void *arguments) > > <snip> > >> +fail: >> + /* Since sizeof errno < PIPE_BUF, the write is atomic. */ >> + ret = -ret; >> + if (ret) >> + while (write_not_cancel (p, &ret, sizeof ret) < 0) >> + continue; >> + exit (SPAWN_ERROR); >> +} > > Sorry for not noticing earlier, but shouldn't it be > "_exit" instead of "exit" when the child fails? Good point. Would you file a bug for this, please? Thanks, Florian
On 30/05/2016 08:02, Florian Weimer wrote: > On 05/29/2016 11:54 AM, Eric Wong wrote: >> Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: >>> +static int >>> +__spawni_child (void *arguments) >> >> <snip> >> >>> +fail: >>> + /* Since sizeof errno < PIPE_BUF, the write is atomic. */ >>> + ret = -ret; >>> + if (ret) >>> + while (write_not_cancel (p, &ret, sizeof ret) < 0) >>> + continue; >>> + exit (SPAWN_ERROR); >>> +} >> >> Sorry for not noticing earlier, but shouldn't it be >> "_exit" instead of "exit" when the child fails? > > Good point. Would you file a bug for this, please? > > Thanks, > Florian Thanks for reporting, I opened BZ#20178. [1] https://sourceware.org/bugzilla/show_bug.cgi?id=20178
Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: > Thanks for reporting, I opened BZ#20178. > > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=20178 Thanks for the quick fix! I also suspect the old/non-Linux sysdeps/posix/spawni.c should be handling POSIX_SPAWN_SETSIGMASK after POSIX_SPAWN_SETSIGDEF like the new Linux one does. This probably won't affect a lot of people, anymore, though.
On 30/05/2016 17:37, Eric Wong wrote: > Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: >> Thanks for reporting, I opened BZ#20178. >> >> [1] https://sourceware.org/bugzilla/show_bug.cgi?id=20178 > > Thanks for the quick fix! > > I also suspect the old/non-Linux sysdeps/posix/spawni.c > should be handling POSIX_SPAWN_SETSIGMASK after POSIX_SPAWN_SETSIGDEF > like the new Linux one does. > > This probably won't affect a lot of people, anymore, though. > I think it indeed make sense, although I would not bother on fixing it now. I will add on my backlog.
diff --git a/include/sched.h b/include/sched.h index 4f59397..b4d7406 100644 --- a/include/sched.h +++ b/include/sched.h @@ -19,7 +19,9 @@ extern int __sched_rr_get_interval (__pid_t __pid, struct timespec *__t); /* These are Linux specific. */ extern int __clone (int (*__fn) (void *__arg), void *__child_stack, int __flags, void *__arg, ...); +libc_hidden_proto (__clone) extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base, size_t __child_stack_size, int __flags, void *__arg, ...); +libc_hidden_proto (__clone2) #endif #endif diff --git a/include/unistd.h b/include/unistd.h index 5152f64..d2802b2 100644 --- a/include/unistd.h +++ b/include/unistd.h @@ -81,6 +81,7 @@ char *__canonicalize_directory_name_internal (const char *__thisdir, size_t __size) attribute_hidden; extern int __dup (int __fd); +libc_hidden_proto (__dup) extern int __dup2 (int __fd, int __fd2); libc_hidden_proto (__dup2) extern int __dup3 (int __fd, int __fd2, int flags); diff --git a/posix/Makefile b/posix/Makefile index 7ec110e..5b0e298 100644 --- a/posix/Makefile +++ b/posix/Makefile @@ -94,7 +94,7 @@ tests := tstgetopt testfnm runtests runptests \ xtests := bug-ga2 ifeq (yes,$(build-shared)) test-srcs := globtest -tests += wordexp-test tst-exec tst-spawn +tests += wordexp-test tst-exec tst-spawn tst-spawn2 endif tests-static = tst-exec-static tst-spawn-static tests += $(tests-static) diff --git a/posix/tst-spawn2.c b/posix/tst-spawn2.c new file mode 100644 index 0000000..41bfde8 --- /dev/null +++ b/posix/tst-spawn2.c @@ -0,0 +1,73 @@ +/* Further tests for spawn in case of invalid binary paths. + Copyright (C) 2016 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <spawn.h> +#include <error.h> +#include <errno.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#include <sys/wait.h> + +#include <stdio.h> + +int +posix_spawn_test (void) +{ + /* Check if posix_spawn correctly returns an error and an invalid pid + by trying to spawn an invalid binary. */ + + const char *program = "/path/to/invalid/binary"; + char * const args[] = { 0 }; + pid_t pid = -1; + + int ret = posix_spawn (&pid, program, 0, 0, args, environ); + if (ret != ENOENT) + error (EXIT_FAILURE, errno, "posix_spawn"); + + /* POSIX states the value returned on pid variable in case of an error + is not specified. GLIBC will update the value iff the child + execution is successful. */ + if (pid != -1) + error (EXIT_FAILURE, errno, "posix_spawn returned pid != -1"); + + /* Check if no child is actually created. */ + ret = waitpid (-1, NULL, 0); + if (ret != -1 || errno != ECHILD) + error (EXIT_FAILURE, errno, "waitpid"); + + /* Same as before, but with posix_spawnp. */ + char *args2[] = { (char*) program, 0 }; + + ret = posix_spawnp (&pid, args2[0], 0, 0, args2, environ); + if (ret != ENOENT) + error (EXIT_FAILURE, errno, "posix_spawnp"); + + if (pid != -1) + error (EXIT_FAILURE, errno, "posix_spawnp returned pid != -1"); + + ret = waitpid (-1, NULL, 0); + if (ret != -1 || errno != ECHILD) + error (EXIT_FAILURE, errno, "waitpid"); + + return 0; +} + +#define TEST_FUNCTION posix_spawn_test () +#include "../test-skeleton.c" + diff --git a/sysdeps/posix/dup.c b/sysdeps/posix/dup.c index 9525e76..abf3ff5 100644 --- a/sysdeps/posix/dup.c +++ b/sysdeps/posix/dup.c @@ -26,5 +26,5 @@ __dup (int fd) { return fcntl (fd, F_DUPFD, 0); } - +libc_hidden_def (__dup) weak_alias (__dup, dup) diff --git a/sysdeps/unix/sysv/linux/aarch64/clone.S b/sysdeps/unix/sysv/linux/aarch64/clone.S index 596fb9c..8f3ab40 100644 --- a/sysdeps/unix/sysv/linux/aarch64/clone.S +++ b/sysdeps/unix/sysv/linux/aarch64/clone.S @@ -93,4 +93,5 @@ thread_start: cfi_endproc .size thread_start, .-thread_start +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/alpha/clone.S b/sysdeps/unix/sysv/linux/alpha/clone.S index ec9c06d..556aa63 100644 --- a/sysdeps/unix/sysv/linux/alpha/clone.S +++ b/sysdeps/unix/sysv/linux/alpha/clone.S @@ -137,4 +137,5 @@ thread_start: cfi_endproc .end thread_start +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/arm/clone.S b/sysdeps/unix/sysv/linux/arm/clone.S index 460a8f5..c103123 100644 --- a/sysdeps/unix/sysv/linux/arm/clone.S +++ b/sysdeps/unix/sysv/linux/arm/clone.S @@ -93,4 +93,5 @@ PSEUDO_END (__clone) .fnend +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/hppa/clone.S b/sysdeps/unix/sysv/linux/hppa/clone.S index e80fd8d..0a18137 100644 --- a/sysdeps/unix/sysv/linux/hppa/clone.S +++ b/sysdeps/unix/sysv/linux/hppa/clone.S @@ -175,4 +175,5 @@ ENTRY(__clone) PSEUDO_END(__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/i386/clone.S b/sysdeps/unix/sysv/linux/i386/clone.S index 7d818c1..ef447d1 100644 --- a/sysdeps/unix/sysv/linux/i386/clone.S +++ b/sysdeps/unix/sysv/linux/i386/clone.S @@ -139,4 +139,5 @@ L(nomoregetpid): cfi_startproc PSEUDO_END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/ia64/clone2.S b/sysdeps/unix/sysv/linux/ia64/clone2.S index 9b257b3..fc046eb 100644 --- a/sysdeps/unix/sysv/linux/ia64/clone2.S +++ b/sysdeps/unix/sysv/linux/ia64/clone2.S @@ -96,6 +96,8 @@ ENTRY(__clone2) ret /* Not reached. */ PSEUDO_END(__clone2) +libc_hidden_def (__clone2) + /* For now we leave __clone undefined. This is unlikely to be a */ /* problem, since at least the i386 __clone in glibc always failed */ /* with a 0 sp (eventhough the kernel explicitly handled it). */ diff --git a/sysdeps/unix/sysv/linux/m68k/clone.S b/sysdeps/unix/sysv/linux/m68k/clone.S index 8b40df2..33474cc 100644 --- a/sysdeps/unix/sysv/linux/m68k/clone.S +++ b/sysdeps/unix/sysv/linux/m68k/clone.S @@ -127,4 +127,5 @@ donepid: cfi_startproc PSEUDO_END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/microblaze/clone.S b/sysdeps/unix/sysv/linux/microblaze/clone.S index 035d88b..cbc95ce 100644 --- a/sysdeps/unix/sysv/linux/microblaze/clone.S +++ b/sysdeps/unix/sysv/linux/microblaze/clone.S @@ -69,4 +69,5 @@ L(thread_start): nop PSEUDO_END(__clone) +libc_hidden_def (__clone) weak_alias (__clone,clone) diff --git a/sysdeps/unix/sysv/linux/mips/clone.S b/sysdeps/unix/sysv/linux/mips/clone.S index 755e8cc..feb8250 100644 --- a/sysdeps/unix/sysv/linux/mips/clone.S +++ b/sysdeps/unix/sysv/linux/mips/clone.S @@ -166,4 +166,5 @@ L(gotpid): END(__thread_start) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/nios2/clone.S b/sysdeps/unix/sysv/linux/nios2/clone.S index 4da5c19..e4d3970 100644 --- a/sysdeps/unix/sysv/linux/nios2/clone.S +++ b/sysdeps/unix/sysv/linux/nios2/clone.S @@ -104,4 +104,5 @@ thread_start: cfi_startproc PSEUDO_END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/nptl-signals.h b/sysdeps/unix/sysv/linux/nptl-signals.h index 7560a21..01f34c2 100644 --- a/sysdeps/unix/sysv/linux/nptl-signals.h +++ b/sysdeps/unix/sysv/linux/nptl-signals.h @@ -16,6 +16,8 @@ License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */ +#include <signal.h> + /* The signal used for asynchronous cancelation. */ #define SIGCANCEL __SIGRTMIN @@ -29,5 +31,13 @@ /* Signal used to implement the setuid et.al. functions. */ #define SIGSETXID (__SIGRTMIN + 1) + +/* Return is sig is used internally. */ +static inline int +__nptl_is_internal_signal (int sig) +{ + return (sig == SIGCANCEL) || (sig == SIGTIMER) || (sig == SIGSETXID); +} + /* Used to communicate with signal handler. */ extern struct xid_command *__xidcmd attribute_hidden; diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S b/sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S index 28948ea..eb973db 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S @@ -108,4 +108,5 @@ L(badargs): cfi_startproc END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S b/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S index c8c6de8..959fdb7 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S @@ -126,4 +126,5 @@ L(parent): END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/s390/s390-32/clone.S b/sysdeps/unix/sysv/linux/s390/s390-32/clone.S index cb2afbb..f774e90 100644 --- a/sysdeps/unix/sysv/linux/s390/s390-32/clone.S +++ b/sysdeps/unix/sysv/linux/s390/s390-32/clone.S @@ -70,4 +70,6 @@ thread_start: xc 0(4,%r15),0(%r15) basr %r14,%r1 /* jump to fn */ DO_CALL (exit, 1) + +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/s390/s390-64/clone.S b/sysdeps/unix/sysv/linux/s390/s390-64/clone.S index eddab35..928a881 100644 --- a/sysdeps/unix/sysv/linux/s390/s390-64/clone.S +++ b/sysdeps/unix/sysv/linux/s390/s390-64/clone.S @@ -73,4 +73,6 @@ thread_start: xc 0(8,%r15),0(%r15) basr %r14,%r1 /* jump to fn */ DO_CALL (exit, 1) + +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/sh/clone.S b/sysdeps/unix/sysv/linux/sh/clone.S index 53cc08b..a73dd7d 100644 --- a/sysdeps/unix/sysv/linux/sh/clone.S +++ b/sysdeps/unix/sysv/linux/sh/clone.S @@ -123,4 +123,5 @@ ENTRY(__clone) .word TID - TLS_PRE_TCB_SIZE PSEUDO_END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/clone.S b/sysdeps/unix/sysv/linux/sparc/sparc32/clone.S index 6f41f0f..68f8202 100644 --- a/sysdeps/unix/sysv/linux/sparc/sparc32/clone.S +++ b/sysdeps/unix/sysv/linux/sparc/sparc32/clone.S @@ -100,4 +100,5 @@ __thread_start: .size __thread_start, .-__thread_start +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/sparc/sparc64/clone.S b/sysdeps/unix/sysv/linux/sparc/sparc64/clone.S index e2d3914..cecffa7 100644 --- a/sysdeps/unix/sysv/linux/sparc/sparc64/clone.S +++ b/sysdeps/unix/sysv/linux/sparc/sparc64/clone.S @@ -96,4 +96,5 @@ __thread_start: .size __thread_start, .-__thread_start +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c new file mode 100644 index 0000000..906cda2 --- /dev/null +++ b/sysdeps/unix/sysv/linux/spawni.c @@ -0,0 +1,401 @@ +/* POSIX spawn interface. Linux version. + Copyright (C) 2016 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <spawn.h> +#include <fcntl.h> +#include <paths.h> +#include <string.h> +#include <sys/resource.h> +#include <sys/wait.h> +#include <sys/param.h> +#include <sys/mman.h> +#include <not-cancel.h> +#include <local-setxid.h> +#include <shlib-compat.h> +#include <nptl/pthreadP.h> +#include <dl-sysdep.h> +#include <ldsodefs.h> +#include <libc-internal.h> +#include "spawn_int.h" + +/* The Linux implementation of posix_spawn{p} uses the clone syscall directly + with CLONE_VM and CLONE_VFORK flags and an allocated stack. The new stack + and start function solves most the vfork limitation (possible parent + clobber due stack spilling). The remaining issue are: + + 1. That no signal handlers must run in child context, to avoid corrupting + parent's state. + 2. The parent must ensure child's stack freeing. + 3. Child must synchronize with parent to enforce 2. and to possible + return execv issues. + + The first issue is solved by blocking all signals in child, even the + NPTL-internal ones (SIGCANCEL and SIGSETXID). The second and third issue + is done by a stack allocation in parent and a synchronization with using + a pipe or waitpid (in case or error). The pipe has the advantage of + allowing the child the communicate an exec error. */ + + +/* The Unix standard contains a long explanation of the way to signal + an error after the fork() was successful. Since no new wait status + was wanted there is no way to signal an error using one of the + available methods. The committee chose to signal an error by a + normal program exit with the exit code 127. */ +#define SPAWN_ERROR 127 + +/* We need to block both SIGCANCEL and SIGSETXID. */ +#define SIGALL_SET \ + ((__sigset_t) { .__val = {[0 ... _SIGSET_NWORDS-1 ] = -1 } }) + +#ifdef __ia64__ +# define CLONE(__fn, __stack, __stacksize, __flags, __args) \ + __clone2 (__fn, __stack, __stacksize, __flags, __args, 0, 0, 0) +#else +# define CLONE(__fn, __stack, __stacksize, __flags, __args) \ + __clone (__fn, __stack, __flags, __args) +#endif + +#if _STACK_GROWS_DOWN +# define STACK(__stack, __stack_size) (__stack + __stack_size) +#elif _STACK_GROWS_UP +# define STACK(__stack, __stack_size) (__stack) +#endif + + +struct posix_spawn_args +{ + int pipe[2]; + sigset_t oldmask; + const char *file; + int (*exec) (const char *, char *const *, char *const *); + const posix_spawn_file_actions_t *fa; + const posix_spawnattr_t *restrict attr; + char *const *argv; + ptrdiff_t argc; + char *const *envp; + int xflags; +}; + +/* Older version requires that shell script without shebang definition + to be called explicitly using /bin/sh (_PATH_BSHELL). */ +static void +maybe_script_execute (struct posix_spawn_args *args) +{ + if (SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_15) + && (args->xflags & SPAWN_XFLAGS_TRY_SHELL) && errno == ENOEXEC) + { + char *const *argv = args->argv; + ptrdiff_t argc = args->argc; + + /* Construct an argument list for the shell. */ + char *new_argv[argc + 1]; + new_argv[0] = (char *) _PATH_BSHELL; + new_argv[1] = (char *) args->file; + memcpy (new_argv + 2, argv + 1, argc * sizeof(char *)); + + /* Execute the shell. */ + args->exec (new_argv[0], new_argv, args->envp); + } +} + +/* Function used in the clone call to setup the signals mask, posix_spawn + attributes, and file actions. It run on its own stack (provided by the + posix_spawn call). */ +static int +__spawni_child (void *arguments) +{ + struct posix_spawn_args *args = arguments; + const posix_spawnattr_t *restrict attr = args->attr; + const posix_spawn_file_actions_t *file_actions = args->fa; + int p = args->pipe[1]; + int ret; + + close_not_cancel (args->pipe[0]); + + /* The child must ensure that no signal handler are enabled because it shared + memory with parent, so the signal disposition must be either SIG_DFL or + SIG_IGN. It does by iterating over all signals and although it could + possibly be more optimized (by tracking which signal potentially have a + signal handler), it might requires system specific solutions (since the + sigset_t data type can be very different on different architectures). */ + struct sigaction sa; + memset (&sa, '\0', sizeof (sa)); + + sigset_t hset; + __sigprocmask (SIG_BLOCK, 0, &hset); + for (int sig = 1; sig < _NSIG; ++sig) + { + if ((attr->__flags & POSIX_SPAWN_SETSIGDEF) + && sigismember (&attr->__sd, sig)) + { + sa.sa_handler = SIG_DFL; + } + else if (sigismember (&hset, sig)) + { + if (__nptl_is_internal_signal (sig)) + sa.sa_handler = SIG_IGN; + else + { + __libc_sigaction (sig, 0, &sa); + if (sa.sa_handler == SIG_IGN) + continue; + sa.sa_handler = SIG_DFL; + } + } + else + continue; + + __libc_sigaction (sig, &sa, 0); + } + +#ifdef _POSIX_PRIORITY_SCHEDULING + /* Set the scheduling algorithm and parameters. */ + if ((attr->__flags & (POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER)) + == POSIX_SPAWN_SETSCHEDPARAM) + { + if ((ret = __sched_setparam (0, &attr->__sp)) == -1) + goto fail; + } + else if ((attr->__flags & POSIX_SPAWN_SETSCHEDULER) != 0) + { + if ((ret = __sched_setscheduler (0, attr->__policy, &attr->__sp)) == -1) + goto fail; + } +#endif + + /* Set the process group ID. */ + if ((attr->__flags & POSIX_SPAWN_SETPGROUP) != 0 + && (ret = __setpgid (0, attr->__pgrp)) != 0) + goto fail; + + /* Set the effective user and group IDs. */ + if ((attr->__flags & POSIX_SPAWN_RESETIDS) != 0 + && ((ret = local_seteuid (__getuid ())) != 0 + || (ret = local_setegid (__getgid ())) != 0)) + goto fail; + + /* Execute the file actions. */ + if (file_actions != 0) + { + int cnt; + struct rlimit64 fdlimit; + bool have_fdlimit = false; + + for (cnt = 0; cnt < file_actions->__used; ++cnt) + { + struct __spawn_action *action = &file_actions->__actions[cnt]; + + /* Dup the pipe fd onto an unoccupied one to avoid any file + operation to clobber it. */ + if ((action->action.close_action.fd == p) + || (action->action.open_action.fd == p) + || (action->action.dup2_action.fd == p)) + { + if ((ret = __dup (p)) < 0) + goto fail; + p = ret; + } + + switch (action->tag) + { + case spawn_do_close: + if ((ret = + close_not_cancel (action->action.close_action.fd)) != 0) + { + if (!have_fdlimit) + { + __getrlimit64 (RLIMIT_NOFILE, &fdlimit); + have_fdlimit = true; + } + + /* Signal errors only for file descriptors out of range. */ + if (action->action.close_action.fd < 0 + || action->action.close_action.fd >= fdlimit.rlim_cur) + goto fail; + } + break; + + case spawn_do_open: + { + ret = open_not_cancel (action->action.open_action.path, + action->action. + open_action.oflag | O_LARGEFILE, + action->action.open_action.mode); + + if (ret == -1) + goto fail; + + int new_fd = ret; + + /* Make sure the desired file descriptor is used. */ + if (ret != action->action.open_action.fd) + { + if ((ret = __dup2 (new_fd, action->action.open_action.fd)) + != action->action.open_action.fd) + goto fail; + + if ((ret = close_not_cancel (new_fd)) != 0) + goto fail; + } + } + break; + + case spawn_do_dup2: + if ((ret = __dup2 (action->action.dup2_action.fd, + action->action.dup2_action.newfd)) + != action->action.dup2_action.newfd) + goto fail; + break; + } + } + } + + /* Set the initial signal mask of the child if POSIX_SPAWN_SETSIGMASK + is set, otherwise restore the previous one. */ + __sigprocmask (SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK) + ? &attr->__ss : &args->oldmask, 0); + + args->exec (args->file, args->argv, args->envp); + + /* This is compatibility function required to enable posix_spawn run + script without shebang definition for older posix_spawn versions + (2.15). */ + maybe_script_execute (args); + + ret = -errno; + +fail: + /* Since sizeof errno < PIPE_BUF, the write is atomic. */ + ret = -ret; + if (ret) + while (write_not_cancel (p, &ret, sizeof ret) < 0) + continue; + exit (SPAWN_ERROR); +} + +/* Spawn a new process executing PATH with the attributes describes in *ATTRP. + Before running the process perform the actions described in FILE-ACTIONS. */ +static int +__spawnix (pid_t * pid, const char *file, + const posix_spawn_file_actions_t * file_actions, + const posix_spawnattr_t * attrp, char *const argv[], + char *const envp[], int xflags, + int (*exec) (const char *, char *const *, char *const *)) +{ + pid_t new_pid; + struct posix_spawn_args args; + int ec; + + if (__pipe2 (args.pipe, O_CLOEXEC)) + return errno; + + /* To avoid imposing hard limits on posix_spawn{p} the total number of + arguments is first calculated to allocate a mmap to hold all possible + values. */ + ptrdiff_t argc = 0; + /* Linux allows at most max (0x7FFFFFFF, 1/4 stack size) arguments + to be used in a execve call. We limit to INT_MAX minus one due the + compatiblity code that may execute a shell script (maybe_script_execute) + where it will construct another argument list with an additional + argument. */ + ptrdiff_t limit = INT_MAX - 1; + while (argv[argc++] != NULL) + if (argc == limit) + { + errno = E2BIG; + return errno; + } + + int prot = (PROT_READ | PROT_WRITE + | ((GL (dl_stack_flags) & PF_X) ? PROT_EXEC : 0)); + + /* Add a slack area for child's stack. */ + size_t argv_size = (argc * sizeof (void *)) + 512; + size_t stack_size = ALIGN_UP (argv_size, GLRO(dl_pagesize)); + void *stack = __mmap (NULL, stack_size, prot, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0); + if (__glibc_unlikely (stack == MAP_FAILED)) + { + close_not_cancel (args.pipe[0]); + close_not_cancel (args.pipe[1]); + return errno; + } + + /* Disable asynchronous cancellation. */ + int cs = LIBC_CANCEL_ASYNC (); + + args.file = file; + args.exec = exec; + args.fa = file_actions; + args.attr = attrp ? attrp : &(const posix_spawnattr_t) { 0 }; + args.argv = argv; + args.argc = argc; + args.envp = envp; + args.xflags = xflags; + + __sigprocmask (SIG_BLOCK, &SIGALL_SET, &args.oldmask); + + /* The clone flags used will create a new child that will run in the same + memory space (CLONE_VM) and the execution of calling thread will be + suspend until the child calls execve or _exit. These condition as + signal below either by pipe write (_exit with SPAWN_ERROR) or + a successful execve. + Also since the calling thread execution will be suspend, there is not + need for CLONE_SETTLS. Although parent and child share the same TLS + namespace, there will be no concurrent access for TLS variables (errno + for instance). */ + new_pid = CLONE (__spawni_child, STACK (stack, stack_size), stack_size, + CLONE_VM | CLONE_VFORK | SIGCHLD, &args); + + close_not_cancel (args.pipe[1]); + + if (new_pid > 0) + { + if (__read (args.pipe[0], &ec, sizeof ec) != sizeof ec) + ec = 0; + else + __waitpid (new_pid, NULL, 0); + } + else + ec = -new_pid; + + __munmap (stack, stack_size); + + close_not_cancel (args.pipe[0]); + + if (!ec && new_pid) + *pid = new_pid; + + __sigprocmask (SIG_SETMASK, &args.oldmask, 0); + + LIBC_CANCEL_RESET (cs); + + return ec; +} + +/* Spawn a new process executing PATH with the attributes describes in *ATTRP. + Before running the process perform the actions described in FILE-ACTIONS. */ +int +__spawni (pid_t * pid, const char *file, + const posix_spawn_file_actions_t * acts, + const posix_spawnattr_t * attrp, char *const argv[], + char *const envp[], int xflags) +{ + return __spawnix (pid, file, acts, attrp, argv, envp, xflags, + xflags & SPAWN_XFLAGS_USE_PATH ? __execvpe : __execve); +} diff --git a/sysdeps/unix/sysv/linux/tile/clone.S b/sysdeps/unix/sysv/linux/tile/clone.S index 02fe3a8..a300eb5 100644 --- a/sysdeps/unix/sysv/linux/tile/clone.S +++ b/sysdeps/unix/sysv/linux/tile/clone.S @@ -219,4 +219,5 @@ ENTRY (__clone) } PSEUDO_END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone) diff --git a/sysdeps/unix/sysv/linux/x86_64/clone.S b/sysdeps/unix/sysv/linux/x86_64/clone.S index 382568a..1a50957 100644 --- a/sysdeps/unix/sysv/linux/x86_64/clone.S +++ b/sysdeps/unix/sysv/linux/x86_64/clone.S @@ -115,4 +115,5 @@ L(thread_start): cfi_startproc; PSEUDO_END (__clone) +libc_hidden_def (__clone) weak_alias (__clone, clone)
This patch implements a new posix_spawn{p} implementation for Linux. The main difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK flags and a direct allocated stack. The new stack and start function solves most the vfork limitation (possible parent clobber due stack spilling). The remaning issue are related to signal handling: 1. That no signal handlers must run in child context, to avoid corrupt parent's state. 2. Child must synchronize with parent to enforce stack deallocation and to possible return execv issues. The first one is solved by blocking all signals in child, even NPTL-internal ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation in parent and a synchronization with using a pipe or waitpid (in case or error). The pipe has the advantage of allowing the child signal an exec error (checked with new tst-spawn2 test). There is an inherent race condition in pipe2 usage for architectures that do not support the syscall directly. In such cases the a pipe plus fctnl is used instead and it may lead to file descriptor leak in parent (as decribed by fcntl documentation). The child process stack is allocate with a mmap with MAP_STACK flag using default architecture stack size. Although it is slower than use a stack buffer from parent, it allows some slack for the compatibility code to run scripts with no shebang (which may use a buffer with size depending of argument list count). Performance should be similar to the vfork default posix implementation and way faster than fork path (vfork on mostly linux ports are basically clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls required for the stack allocation/deallocation. It fixes BZ#10354, BZ#14750, and BZ#18433. Tested on i386, x86_64, powerpc64le, and aarch64. [BZ #14750] [BZ #10354] [BZ #18433] * include/sched.h (__clone): Add hidden prototype. (__clone2): Likewise. * include/unistd.h (__dup): Likewise. * posix/Makefile (tests): Add tst-spawn2. * posix/tst-spawn2.c: New file. * sysdeps/posix/dup.c (__dup): Add hidden definition. * sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/alpha/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/arm/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/hppa/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/i386/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/ia64/clone2.S (__clone): Likewise. * sysdeps/unix/sysv/linux/m68k/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/microblaze/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/mips/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/nios2/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/s390/s390-32/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/s390/s390-64/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/sh/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/sparc/sparc32/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/sparc/sparc64/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/tile/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/x86_64/clone.S (__clone): Likewise. * sysdeps/unix/sysv/linux/nptl-signals.h (____nptl_is_internal_signal): New function. * sysdeps/unix/sysv/linux/spawni.c: New file. --- include/sched.h | 2 + include/unistd.h | 1 + posix/Makefile | 2 +- posix/tst-spawn2.c | 73 ++++ sysdeps/posix/dup.c | 2 +- sysdeps/unix/sysv/linux/aarch64/clone.S | 1 + sysdeps/unix/sysv/linux/alpha/clone.S | 1 + sysdeps/unix/sysv/linux/arm/clone.S | 1 + sysdeps/unix/sysv/linux/hppa/clone.S | 1 + sysdeps/unix/sysv/linux/i386/clone.S | 1 + sysdeps/unix/sysv/linux/ia64/clone2.S | 2 + sysdeps/unix/sysv/linux/m68k/clone.S | 1 + sysdeps/unix/sysv/linux/microblaze/clone.S | 1 + sysdeps/unix/sysv/linux/mips/clone.S | 1 + sysdeps/unix/sysv/linux/nios2/clone.S | 1 + sysdeps/unix/sysv/linux/nptl-signals.h | 10 + sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S | 1 + sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S | 1 + sysdeps/unix/sysv/linux/s390/s390-32/clone.S | 2 + sysdeps/unix/sysv/linux/s390/s390-64/clone.S | 2 + sysdeps/unix/sysv/linux/sh/clone.S | 1 + sysdeps/unix/sysv/linux/sparc/sparc32/clone.S | 1 + sysdeps/unix/sysv/linux/sparc/sparc64/clone.S | 1 + sysdeps/unix/sysv/linux/spawni.c | 401 ++++++++++++++++++++++ sysdeps/unix/sysv/linux/tile/clone.S | 1 + sysdeps/unix/sysv/linux/x86_64/clone.S | 1 + 27 files changed, 545 insertions(+), 2 deletions(-) create mode 100644 posix/tst-spawn2.c create mode 100644 sysdeps/unix/sysv/linux/spawni.c