diff mbox series

[RFC,04/13] x86/um: nommu: syscall handling

Message ID 1a39a239b4a34d2f613ab1ffc62c80967a2f57fb.1729770373.git.thehajime@gmail.com
State RFC
Headers show
Series [RFC,01/13] fs: binfmt_elf_efpic: add architecture hook elf_arch_finalize_exec | expand

Commit Message

Hajime Tazaki Oct. 24, 2024, 12:09 p.m. UTC 
This commit introduces an entry point of syscall interface for !MMU
mode. It uses an entry function, __kernel_vsyscall, a kernel-wide global
symbol accessible from any locations.

Although it isn't in the scope of this commit, it can be also exposed
via vdso image which is directly accessible from userspace. A standard
library (i.e., libc) can utilize this entry point to implement syscall
wrapper; we can also use this by hooking syscall for unmodified userspace
applications/libraries, which will be implemented in the subsequent
commit.

This only supports 64-bit mode of x86 architecture.

Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
Signed-off-by: Ricardo Koller <ricarkol@google.com>
---
 arch/x86/um/do_syscall_64.c             | 42 ++++++++++++
 arch/x86/um/entry_64.S                  | 88 +++++++++++++++++++++++++
 arch/x86/um/shared/sysdep/syscalls_64.h |  4 ++
 3 files changed, 134 insertions(+)
 create mode 100644 arch/x86/um/do_syscall_64.c
 create mode 100644 arch/x86/um/entry_64.S

Comments

Johannes Berg Oct. 25, 2024, 9:14 a.m. UTC | #1 
On Thu, 2024-10-24 at 21:09 +0900, Hajime Tazaki wrote:
> 
> +++ b/arch/x86/um/do_syscall_64.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/kernel.h>
> +#include <linux/ptrace.h>
> +#include <kern_util.h>
> +#include <sysdep/syscalls.h>
> +#include <os.h>
> +
> +#ifndef CONFIG_MMU

This seems unnecessary, you don't build the file with CONFIG_MMU in the
first place.

> +++ b/arch/x86/um/entry_64.S
> @@ -0,0 +1,88 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#include <asm/errno.h>
> +
> +#include <linux/linkage.h>
> +#include <asm/percpu.h>
> +#include <asm/desc.h>
> +
> +#include "../entry/calling.h"
> +
> +#ifdef CONFIG_SMP
> +#error need to stash these variables somewhere else
> +#endif
> +
> +#ifndef CONFIG_MMU

same here.

> +++ b/arch/x86/um/shared/sysdep/syscalls_64.h
> @@ -25,4 +25,8 @@ extern syscall_handler_t *sys_call_table[];
>  extern syscall_handler_t sys_modify_ldt;
>  extern syscall_handler_t sys_arch_prctl;
>  
> +__visible void do_syscall_64(struct pt_regs *regs);
> +extern long __kernel_vsyscall(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
> +			      int64_t a4, int64_t a5, int64_t a6);
> +
> 

but maybe that should be ifdef'ed?

johannes
Hajime Tazaki Oct. 25, 2024, 12:55 p.m. UTC | #2 
On Fri, 25 Oct 2024 18:14:19 +0900,
Johannes Berg wrote:
> 
> On Thu, 2024-10-24 at 21:09 +0900, Hajime Tazaki wrote:
> > 
> > +++ b/arch/x86/um/do_syscall_64.c
> > @@ -0,0 +1,42 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/ptrace.h>
> > +#include <kern_util.h>
> > +#include <sysdep/syscalls.h>
> > +#include <os.h>
> > +
> > +#ifndef CONFIG_MMU
> 
> This seems unnecessary, you don't build the file with CONFIG_MMU in the
> first place.

will fix it.

> > +++ b/arch/x86/um/entry_64.S
> > @@ -0,0 +1,88 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#include <asm/errno.h>
> > +
> > +#include <linux/linkage.h>
> > +#include <asm/percpu.h>
> > +#include <asm/desc.h>
> > +
> > +#include "../entry/calling.h"
> > +
> > +#ifdef CONFIG_SMP
> > +#error need to stash these variables somewhere else
> > +#endif
> > +
> > +#ifndef CONFIG_MMU
> 
> same here.

will fix it too.

> > +++ b/arch/x86/um/shared/sysdep/syscalls_64.h
> > @@ -25,4 +25,8 @@ extern syscall_handler_t *sys_call_table[];
> >  extern syscall_handler_t sys_modify_ldt;
> >  extern syscall_handler_t sys_arch_prctl;
> >  
> > +__visible void do_syscall_64(struct pt_regs *regs);
> > +extern long __kernel_vsyscall(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
> > +			      int64_t a4, int64_t a5, int64_t a6);
> > +
> > 
> 
> but maybe that should be ifdef'ed?

thanks, will fix it too.

-- Hajime
diff mbox series

Patch

diff --git a/arch/x86/um/do_syscall_64.c b/arch/x86/um/do_syscall_64.c
new file mode 100644
index 000000000000..7af6e881ad58
--- /dev/null
+++ b/arch/x86/um/do_syscall_64.c
@@ -0,0 +1,42 @@ 
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+#include <linux/ptrace.h>
+#include <kern_util.h>
+#include <sysdep/syscalls.h>
+#include <os.h>
+
+#ifndef CONFIG_MMU
+
+__visible void do_syscall_64(struct pt_regs *regs)
+{
+	int syscall;
+
+	syscall = PT_SYSCALL_NR(regs->regs.gp);
+	UPT_SYSCALL_NR(&regs->regs) = syscall;
+
+	pr_debug("syscall(%d) (current=%lx) (fn=%lx)\n",
+		 syscall, (unsigned long)current,
+		 (unsigned long)sys_call_table[syscall]);
+
+	if (likely(syscall < NR_syscalls)) {
+		PT_REGS_SET_SYSCALL_RETURN(regs,
+				EXECUTE_SYSCALL(syscall, regs));
+	}
+
+	pr_debug("syscall(%d) --> %lx\n", syscall,
+		regs->regs.gp[HOST_AX]);
+
+	PT_REGS_SYSCALL_RET(regs) = regs->regs.gp[HOST_AX];
+
+	/* force do_signal() --> is_syscall() */
+	set_thread_flag(TIF_SIGPENDING);
+	interrupt_end();
+
+	/* execve succeeded */
+	if (syscall == __NR_execve && regs->regs.gp[HOST_AX] == 0) {
+		userspace(&current->thread.regs.regs,
+			current_thread_info()->aux_fp_regs);
+	}
+}
+#endif
diff --git a/arch/x86/um/entry_64.S b/arch/x86/um/entry_64.S
new file mode 100644
index 000000000000..12e11ac03543
--- /dev/null
+++ b/arch/x86/um/entry_64.S
@@ -0,0 +1,88 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <asm/errno.h>
+
+#include <linux/linkage.h>
+#include <asm/percpu.h>
+#include <asm/desc.h>
+
+#include "../entry/calling.h"
+
+#ifdef CONFIG_SMP
+#error need to stash these variables somewhere else
+#endif
+
+#ifndef CONFIG_MMU
+#define UM_GLOBAL_VAR(x) .data; .align 8; .globl x; x:; .long 0
+
+UM_GLOBAL_VAR(current_top_of_stack)
+UM_GLOBAL_VAR(current_ptregs)
+
+.code64
+.section .entry.text, "ax"
+
+.align 8
+#undef ENTRY
+#define ENTRY(x) .text; .globl x; .type x,%function; x:
+#undef END
+#define END(x)   .size x, . - x
+
+/*
+ * %rcx has the return address (we set it like that in zpoline trampoline).
+ *
+ * Registers on entry:
+ * rax  system call number
+ * rcx  return address
+ * rdi  arg0
+ * rsi  arg1
+ * rdx  arg2
+ * r10  arg3
+ * r8   arg4
+ * r9   arg5
+ *
+ * (note: we are allowed to mess with r11: r11 is callee-clobbered
+ * register in C ABI)
+ */
+ENTRY(__kernel_vsyscall)
+
+	movq	%rsp, %r11
+
+	/* Point rsp to the top of the ptregs array, so we can
+           just fill it with a bunch of push'es. */
+	movq	current_ptregs, %rsp
+
+	/* 8 bytes * 20 registers (plus 8 for the push) */
+	addq	$168, %rsp
+
+	/* Construct struct pt_regs on stack */
+	pushq	$0		/* pt_regs->ss (index 20) */
+	pushq   %r11		/* pt_regs->sp */
+	pushfq			/* pt_regs->flags */
+	pushq	$0		/* pt_regs->cs */
+	pushq	%rcx		/* pt_regs->ip */
+	pushq	%rax		/* pt_regs->orig_ax */
+
+	PUSH_AND_CLEAR_REGS rax=$-ENOSYS
+
+	mov %rsp, %rdi
+
+	/*
+	 * Switch to current top of stack, so "current->" points
+	 * to the right task.
+	 */
+	movq	current_top_of_stack, %rsp
+
+	call	do_syscall_64
+
+	movq	current_ptregs, %rsp
+
+	POP_REGS
+
+	addq	$8, %rsp	/* skip orig_ax */
+	addq	$8, %rsp	/* skip ip */
+	addq	$8, %rsp	/* skip cs */
+	addq	$8, %rsp	/* skip flags */
+	popq	%rsp
+
+	ret
+
+END(__kernel_vsyscall)
diff --git a/arch/x86/um/shared/sysdep/syscalls_64.h b/arch/x86/um/shared/sysdep/syscalls_64.h
index b6b997225841..31aa0694cec0 100644
--- a/arch/x86/um/shared/sysdep/syscalls_64.h
+++ b/arch/x86/um/shared/sysdep/syscalls_64.h
@@ -25,4 +25,8 @@  extern syscall_handler_t *sys_call_table[];
 extern syscall_handler_t sys_modify_ldt;
 extern syscall_handler_t sys_arch_prctl;
 
+__visible void do_syscall_64(struct pt_regs *regs);
+extern long __kernel_vsyscall(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
+			      int64_t a4, int64_t a5, int64_t a6);
+
 #endif