diff mbox series

aarch64, libgcc: Fix unwinding from pac-ret to normal frames [PR94514]

Message ID 20200409141948.GF987@arm.com
State New
Headers show
Series aarch64, libgcc: Fix unwinding from pac-ret to normal frames [PR94514] | expand

Commit Message

Szabolcs Nagy April 9, 2020, 2:19 p.m. UTC 
With -mbranch-protection=pac-ret the debug info toggles the
signedness state of the return address so the unwinder knows when
the return address needs pointer authentication.

The unwind context flags were not updated according to the dwarf
frame info.

This causes unwinding across frames that were built without pac-ret
to incorrectly authenticate the return address wich corrupts the
return address on a system where PAuth is enabled.

Note: This even affects systems where all code use pac-ret because
unwinding across a signal frame the return address is not signed.

gcc/testsuite/ChangeLog:

2020-04-XX  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	PR target/94514
	* g++.target/aarch64/pr94514.C: New test.
	* gcc.target/aarch64/pr94514.c: New test.

libgcc/ChangeLog:

2020-04-XX  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	PR target/94514
	* config/aarch64/aarch64-unwind.h (aarch64_frob_update_context):
	Update context->flags accroding to the frame state.
---
 gcc/testsuite/g++.target/aarch64/pr94514.C | 26 ++++++++
 gcc/testsuite/gcc.target/aarch64/pr94514.c | 76 ++++++++++++++++++++++
 libgcc/config/aarch64/aarch64-unwind.h     |  2 +
 3 files changed, 104 insertions(+)
 create mode 100644 gcc/testsuite/g++.target/aarch64/pr94514.C
 create mode 100644 gcc/testsuite/gcc.target/aarch64/pr94514.c

Comments

Kyrylo Tkachov April 17, 2020, 10:05 a.m. UTC | #1 
Hi Szabolcs,

> -----Original Message-----
> From: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
> Sent: 09 April 2020 15:20
> To: gcc-patches@gcc.gnu.org
> Cc: Richard Earnshaw <Richard.Earnshaw@arm.com>; Richard Sandiford
> <Richard.Sandiford@arm.com>; Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>
> Subject: [PATCH] aarch64, libgcc: Fix unwinding from pac-ret to normal
> frames [PR94514]
> 
> With -mbranch-protection=pac-ret the debug info toggles the
> signedness state of the return address so the unwinder knows when
> the return address needs pointer authentication.
> 
> The unwind context flags were not updated according to the dwarf
> frame info.
> 
> This causes unwinding across frames that were built without pac-ret
> to incorrectly authenticate the return address wich corrupts the
> return address on a system where PAuth is enabled.
> 
> Note: This even affects systems where all code use pac-ret because
> unwinding across a signal frame the return address is not signed.
> 

Ok, I'm guessing this needs backporting?
Thanks,
Kyrill

> gcc/testsuite/ChangeLog:
> 
> 2020-04-XX  Szabolcs Nagy  <szabolcs.nagy@arm.com>
> 
> 	PR target/94514
> 	* g++.target/aarch64/pr94514.C: New test.
> 	* gcc.target/aarch64/pr94514.c: New test.
> 
> libgcc/ChangeLog:
> 
> 2020-04-XX  Szabolcs Nagy  <szabolcs.nagy@arm.com>
> 
> 	PR target/94514
> 	* config/aarch64/aarch64-unwind.h (aarch64_frob_update_context):
> 	Update context->flags accroding to the frame state.
> ---
>  gcc/testsuite/g++.target/aarch64/pr94514.C | 26 ++++++++
>  gcc/testsuite/gcc.target/aarch64/pr94514.c | 76 ++++++++++++++++++++++
>  libgcc/config/aarch64/aarch64-unwind.h     |  2 +
>  3 files changed, 104 insertions(+)
>  create mode 100644 gcc/testsuite/g++.target/aarch64/pr94514.C
>  create mode 100644 gcc/testsuite/gcc.target/aarch64/pr94514.c
> 
> diff --git a/gcc/testsuite/g++.target/aarch64/pr94514.C
> b/gcc/testsuite/g++.target/aarch64/pr94514.C
> new file mode 100644
> index 00000000000..2a8c949ba30
> --- /dev/null
> +++ b/gcc/testsuite/g++.target/aarch64/pr94514.C
> @@ -0,0 +1,26 @@
> +/* PR target/94514. Unwind across mixed pac-ret and non-pac-ret frames.
> */
> +/* { dg-do run } */
> +
> +__attribute__((noinline, target("branch-protection=pac-ret")))
> +static void do_throw (void)
> +{
> +  throw 42;
> +  __builtin_abort ();
> +}
> +
> +__attribute__((noinline, target("branch-protection=none")))
> +static void no_pac_ret (void)
> +{
> +  do_throw ();
> +  __builtin_abort ();
> +}
> +
> +int main ()
> +{
> +  try {
> +    no_pac_ret ();
> +  } catch (...) {
> +    return 0;
> +  }
> +  __builtin_abort ();
> +}
> diff --git a/gcc/testsuite/gcc.target/aarch64/pr94514.c
> b/gcc/testsuite/gcc.target/aarch64/pr94514.c
> new file mode 100644
> index 00000000000..bbbf5a6b0b3
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/pr94514.c
> @@ -0,0 +1,76 @@
> +/* PR target/94514. Unwind across mixed pac-ret and non-pac-ret frames.
> */
> +/* { dg-do run } */
> +/* { dg-options "-fexceptions -O2" } */
> +
> +#include <unwind.h>
> +#include <stdlib.h>
> +#include <stdio.h>
> +
> +#define die() \
> +  do { \
> +    printf ("%s:%d: reached unexpectedly.\n", __FILE__, __LINE__); \
> +    fflush (stdout); \
> +    abort (); \
> +  } while (0)
> +
> +static struct _Unwind_Exception exc;
> +
> +static _Unwind_Reason_Code
> +force_unwind_stop (int version, _Unwind_Action actions,
> +                   _Unwind_Exception_Class exc_class,
> +                   struct _Unwind_Exception *exc_obj,
> +                   struct _Unwind_Context *context,
> +                   void *stop_parameter)
> +{
> +  printf ("%s: CFA: %p PC: %p actions: %d\n",
> +	  __func__,
> +	  (void *)_Unwind_GetCFA (context),
> +	  (void *)_Unwind_GetIP (context),
> +	  (int)actions);
> +  if (actions & _UA_END_OF_STACK)
> +    die ();
> +  return _URC_NO_REASON;
> +}
> +
> +static void force_unwind (void)
> +{
> +#ifndef __USING_SJLJ_EXCEPTIONS__
> +  _Unwind_ForcedUnwind (&exc, force_unwind_stop, 0);
> +#else
> +  _Unwind_SjLj_ForcedUnwind (&exc, force_unwind_stop, 0);
> +#endif
> +}
> +
> +__attribute__((noinline, target("branch-protection=pac-ret")))
> +static void f2_pac_ret (void)
> +{
> +  force_unwind ();
> +  die ();
> +}
> +
> +__attribute__((noinline, target("branch-protection=none")))
> +static void f1_no_pac_ret (void)
> +{
> +  f2_pac_ret ();
> +  die ();
> +}
> +
> +__attribute__((noinline, target("branch-protection=pac-ret")))
> +static void f0_pac_ret (void)
> +{
> +  f1_no_pac_ret ();
> +  die ();
> +}
> +
> +static void cleanup_handler (void *p)
> +{
> +  printf ("%s: Success.\n", __func__);
> +  exit (0);
> +}
> +
> +int main ()
> +{
> +  char dummy __attribute__((cleanup (cleanup_handler)));
> +  f0_pac_ret ();
> +  die ();
> +}
> diff --git a/libgcc/config/aarch64/aarch64-unwind.h
> b/libgcc/config/aarch64/aarch64-unwind.h
> index 4c8790bae67..ed84a96db41 100644
> --- a/libgcc/config/aarch64/aarch64-unwind.h
> +++ b/libgcc/config/aarch64/aarch64-unwind.h
> @@ -104,6 +104,8 @@ aarch64_frob_update_context (struct
> _Unwind_Context *context,
>    if (fs->regs.reg[DWARF_REGNUM_AARCH64_RA_STATE].loc.offset & 0x1)
>      /* The flag is used for re-authenticating EH handler's address.  */
>      context->flags |= RA_SIGNED_BIT;
> +  else
> +    context->flags &= ~RA_SIGNED_BIT;
> 
>    return;
>  }
> --
> 2.17.1
Szabolcs Nagy April 21, 2020, 4:52 p.m. UTC | #2 
The 04/17/2020 11:05, Kyrylo Tkachov wrote:
> Hi Szabolcs,
> 
> > -----Original Message-----
> > From: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
> > Sent: 09 April 2020 15:20
> > To: gcc-patches@gcc.gnu.org
> > Cc: Richard Earnshaw <Richard.Earnshaw@arm.com>; Richard Sandiford
> > <Richard.Sandiford@arm.com>; Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>
> > Subject: [PATCH] aarch64, libgcc: Fix unwinding from pac-ret to normal
> > frames [PR94514]
> >
> > With -mbranch-protection=pac-ret the debug info toggles the
> > signedness state of the return address so the unwinder knows when
> > the return address needs pointer authentication.
> >
> > The unwind context flags were not updated according to the dwarf
> > frame info.
> >
> > This causes unwinding across frames that were built without pac-ret
> > to incorrectly authenticate the return address wich corrupts the
> > return address on a system where PAuth is enabled.
> >
> > Note: This even affects systems where all code use pac-ret because
> > unwinding across a signal frame the return address is not signed.
> >
> 
> Ok, I'm guessing this needs backporting?

committed now,

yes i think it has to go back to gcc-9 and gcc-8,
i will do that later. thanks.
Christophe Lyon April 22, 2020, 1:22 p.m. UTC | #3 
Hi,


On Tue, 21 Apr 2020 at 18:52, Szabolcs Nagy <Szabolcs.Nagy@arm.com> wrote:
>
> The 04/17/2020 11:05, Kyrylo Tkachov wrote:
> > Hi Szabolcs,
> >
> > > -----Original Message-----
> > > From: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
> > > Sent: 09 April 2020 15:20
> > > To: gcc-patches@gcc.gnu.org
> > > Cc: Richard Earnshaw <Richard.Earnshaw@arm.com>; Richard Sandiford
> > > <Richard.Sandiford@arm.com>; Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>
> > > Subject: [PATCH] aarch64, libgcc: Fix unwinding from pac-ret to normal
> > > frames [PR94514]
> > >
> > > With -mbranch-protection=pac-ret the debug info toggles the
> > > signedness state of the return address so the unwinder knows when
> > > the return address needs pointer authentication.
> > >
> > > The unwind context flags were not updated according to the dwarf
> > > frame info.
> > >
> > > This causes unwinding across frames that were built without pac-ret
> > > to incorrectly authenticate the return address wich corrupts the
> > > return address on a system where PAuth is enabled.
> > >
> > > Note: This even affects systems where all code use pac-ret because
> > > unwinding across a signal frame the return address is not signed.
> > >
> >
> > Ok, I'm guessing this needs backporting?
>
> committed now,
>
> yes i think it has to go back to gcc-9 and gcc-8,
> i will do that later. thanks.

The new test fails with ilp32, not sure if that's supposed to work?

FAIL: gcc.target/aarch64/pr94514.c (test for excess errors)
Excess errors:
/gcc/testsuite/gcc.target/aarch64/pr94514.c:27:4: warning: cast to
pointer from integer of different size [-Wint-to-pointer-cast]

spawn /aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-elf/invoke-foundation-v8-bare-metal.sh
./pr94514.exe
force_unwind_stop: CFA: 0xefffff80 PC: 0x80001304 actions: 10
force_unwind_stop: CFA: 0xefffff90 PC: 0x8000133c actions: 10
Terminated by exception.

*** EXIT code 126
gcc.target/aarch64/pr94514.c execution test (reason: TCL LOOKUP CHANNEL exp7)
FAIL: gcc.target/aarch64/pr94514.c execution test

(executed using the Foundation Model)


The C++ test compiles without warnings, but fails at execution too
(without the force_unwind_stop traces):
PASS: g++.target/aarch64/pr94514.C (test for excess errors)
spawn /aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-elf/invoke-foundation-v8-bare-metal.sh
./pr94514.exe
Terminated by exception.

*** EXIT code 126
g++.target/aarch64/pr94514.C execution test (reason: TCL LOOKUP CHANNEL exp7)
FAIL: g++.target/aarch64/pr94514.C execution test

Maybe you just want to skip the test for ilp32?

Thanks,

Christophe
Szabolcs Nagy April 23, 2020, 1:18 p.m. UTC | #4 
The 04/22/2020 15:22, Christophe Lyon wrote:
> The new test fails with ilp32, not sure if that's supposed to work?
> 
> FAIL: gcc.target/aarch64/pr94514.c (test for excess errors)
> Excess errors:
> /gcc/testsuite/gcc.target/aarch64/pr94514.c:27:4: warning: cast to
> pointer from integer of different size [-Wint-to-pointer-cast]
> 
> spawn /aci-gcc-fsf/builds/gcc-fsf-gccsrc/tools/aarch64-none-elf/invoke-foundation-v8-bare-metal.sh
> ./pr94514.exe
> force_unwind_stop: CFA: 0xefffff80 PC: 0x80001304 actions: 10
> force_unwind_stop: CFA: 0xefffff90 PC: 0x8000133c actions: 10
> Terminated by exception.
> 
> *** EXIT code 126
> gcc.target/aarch64/pr94514.c execution test (reason: TCL LOOKUP CHANNEL exp7)
> FAIL: gcc.target/aarch64/pr94514.c execution test
> 
> (executed using the Foundation Model)
> 
> 
> The C++ test compiles without warnings, but fails at execution too
...
> Maybe you just want to skip the test for ilp32?

i didn't test ilp32, i would expect a compile time error for

__attribute__((target("branch-protection=pac-ret")))

on ilp32, or just ignoring it (which would have worked),
runtime error for this on a pac-enabled system is nasty.

i disabled the test on ilp32 as an obvious fix (attached),
and raised PR94729 for the attribute handling in ilp32.

thanks for catching this.
diff mbox series

Patch

diff --git a/gcc/testsuite/g++.target/aarch64/pr94514.C b/gcc/testsuite/g++.target/aarch64/pr94514.C
new file mode 100644
index 00000000000..2a8c949ba30
--- /dev/null
+++ b/gcc/testsuite/g++.target/aarch64/pr94514.C
@@ -0,0 +1,26 @@ 
+/* PR target/94514. Unwind across mixed pac-ret and non-pac-ret frames.  */
+/* { dg-do run } */
+
+__attribute__((noinline, target("branch-protection=pac-ret")))
+static void do_throw (void)
+{
+  throw 42;
+  __builtin_abort ();
+}
+
+__attribute__((noinline, target("branch-protection=none")))
+static void no_pac_ret (void)
+{
+  do_throw ();
+  __builtin_abort ();
+}
+
+int main ()
+{
+  try {
+    no_pac_ret ();
+  } catch (...) {
+    return 0;
+  }
+  __builtin_abort ();
+}
diff --git a/gcc/testsuite/gcc.target/aarch64/pr94514.c b/gcc/testsuite/gcc.target/aarch64/pr94514.c
new file mode 100644
index 00000000000..bbbf5a6b0b3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr94514.c
@@ -0,0 +1,76 @@ 
+/* PR target/94514. Unwind across mixed pac-ret and non-pac-ret frames.  */
+/* { dg-do run } */
+/* { dg-options "-fexceptions -O2" } */
+
+#include <unwind.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#define die() \
+  do { \
+    printf ("%s:%d: reached unexpectedly.\n", __FILE__, __LINE__); \
+    fflush (stdout); \
+    abort (); \
+  } while (0)
+
+static struct _Unwind_Exception exc;
+
+static _Unwind_Reason_Code
+force_unwind_stop (int version, _Unwind_Action actions,
+                   _Unwind_Exception_Class exc_class,
+                   struct _Unwind_Exception *exc_obj,
+                   struct _Unwind_Context *context,
+                   void *stop_parameter)
+{
+  printf ("%s: CFA: %p PC: %p actions: %d\n",
+	  __func__,
+	  (void *)_Unwind_GetCFA (context),
+	  (void *)_Unwind_GetIP (context),
+	  (int)actions);
+  if (actions & _UA_END_OF_STACK)
+    die ();
+  return _URC_NO_REASON;
+}
+
+static void force_unwind (void)
+{
+#ifndef __USING_SJLJ_EXCEPTIONS__
+  _Unwind_ForcedUnwind (&exc, force_unwind_stop, 0);
+#else
+  _Unwind_SjLj_ForcedUnwind (&exc, force_unwind_stop, 0);
+#endif
+}
+
+__attribute__((noinline, target("branch-protection=pac-ret")))
+static void f2_pac_ret (void)
+{
+  force_unwind ();
+  die ();
+}
+
+__attribute__((noinline, target("branch-protection=none")))
+static void f1_no_pac_ret (void)
+{
+  f2_pac_ret ();
+  die ();
+}
+
+__attribute__((noinline, target("branch-protection=pac-ret")))
+static void f0_pac_ret (void)
+{
+  f1_no_pac_ret ();
+  die ();
+}
+
+static void cleanup_handler (void *p)
+{
+  printf ("%s: Success.\n", __func__);
+  exit (0);
+}
+
+int main ()
+{
+  char dummy __attribute__((cleanup (cleanup_handler)));
+  f0_pac_ret ();
+  die ();
+}
diff --git a/libgcc/config/aarch64/aarch64-unwind.h b/libgcc/config/aarch64/aarch64-unwind.h
index 4c8790bae67..ed84a96db41 100644
--- a/libgcc/config/aarch64/aarch64-unwind.h
+++ b/libgcc/config/aarch64/aarch64-unwind.h
@@ -104,6 +104,8 @@  aarch64_frob_update_context (struct _Unwind_Context *context,
   if (fs->regs.reg[DWARF_REGNUM_AARCH64_RA_STATE].loc.offset & 0x1)
     /* The flag is used for re-authenticating EH handler's address.  */
     context->flags |= RA_SIGNED_BIT;
+  else
+    context->flags &= ~RA_SIGNED_BIT;
 
   return;
 }