diff mbox series

stack-protector: Check stack canary for noreturn function

Message ID 20220714215522.359952-1-hjl.tools@gmail.com
State New
Headers show
Series stack-protector: Check stack canary for noreturn function | expand

Commit Message

H.J. Lu July 14, 2022, 9:55 p.m. UTC 
Check stack canary for noreturn function to catch stack corruption
before calling noreturn function.  For C++, check stack canary when
throwing exception or resuming stack unwind to avoid corrupted stack.

gcc/

	PR middle-end/58245
	* calls.cc (expand_call): Check stack canary for noreturn
	function.

gcc/testsuite/

	PR middle-end/58245
	* c-c++-common/pr58245-1.c: New test.
	* g++.dg/pr58245-1.C: Likewise.
	* g++.dg/fstack-protector-strong.C: Adjusted.
---
 gcc/calls.cc                                   |  7 ++++++-
 gcc/testsuite/c-c++-common/pr58245-1.c         | 12 ++++++++++++
 gcc/testsuite/g++.dg/fstack-protector-strong.C |  2 +-
 gcc/testsuite/g++.dg/pr58245-1.C               | 10 ++++++++++
 4 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/pr58245-1.c
 create mode 100644 gcc/testsuite/g++.dg/pr58245-1.C

Comments

Jeff Law July 30, 2022, 8:30 p.m. UTC | #1 
On 7/14/2022 3:55 PM, H.J. Lu via Gcc-patches wrote:
> Check stack canary for noreturn function to catch stack corruption
> before calling noreturn function.  For C++, check stack canary when
> throwing exception or resuming stack unwind to avoid corrupted stack.
>
> gcc/
>
> 	PR middle-end/58245
> 	* calls.cc (expand_call): Check stack canary for noreturn
> 	function.
>
> gcc/testsuite/
>
> 	PR middle-end/58245
> 	* c-c++-common/pr58245-1.c: New test.
> 	* g++.dg/pr58245-1.C: Likewise.
> 	* g++.dg/fstack-protector-strong.C: Adjusted.
But is this really something we want?   I'd actually lean towards 
eliminating the useless load -- I don't necessarily think we should be 
treating non-returning paths specially here.

The whole point of the stack protector is to prevent the *return* path 
from going to an attacker controlled location.  I'm not sure checking 
the protector at this point actually does anything particularly useful.

jeff
H.J. Lu Aug. 2, 2022, 5:43 p.m. UTC | #2 
On Sat, Jul 30, 2022 at 1:30 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 7/14/2022 3:55 PM, H.J. Lu via Gcc-patches wrote:
> > Check stack canary for noreturn function to catch stack corruption
> > before calling noreturn function.  For C++, check stack canary when
> > throwing exception or resuming stack unwind to avoid corrupted stack.
> >
> > gcc/
> >
> >       PR middle-end/58245
> >       * calls.cc (expand_call): Check stack canary for noreturn
> >       function.
> >
> > gcc/testsuite/
> >
> >       PR middle-end/58245
> >       * c-c++-common/pr58245-1.c: New test.
> >       * g++.dg/pr58245-1.C: Likewise.
> >       * g++.dg/fstack-protector-strong.C: Adjusted.
> But is this really something we want?   I'd actually lean towards
> eliminating the useless load -- I don't necessarily think we should be
> treating non-returning paths specially here.
>
> The whole point of the stack protector is to prevent the *return* path
> from going to an attacker controlled location.  I'm not sure checking
> the protector at this point actually does anything particularly useful.

throw is marked no return.   Since the unwind library may read
the stack contents to unwind stack, it the stack is corrupted, the
exception handling may go wrong.   Should we handle this case?

 --
H.J.
Jeff Law Aug. 2, 2022, 11:34 p.m. UTC | #3 
On 8/2/2022 11:43 AM, H.J. Lu wrote:
> On Sat, Jul 30, 2022 at 1:30 PM Jeff Law via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>>
>> On 7/14/2022 3:55 PM, H.J. Lu via Gcc-patches wrote:
>>> Check stack canary for noreturn function to catch stack corruption
>>> before calling noreturn function.  For C++, check stack canary when
>>> throwing exception or resuming stack unwind to avoid corrupted stack.
>>>
>>> gcc/
>>>
>>>        PR middle-end/58245
>>>        * calls.cc (expand_call): Check stack canary for noreturn
>>>        function.
>>>
>>> gcc/testsuite/
>>>
>>>        PR middle-end/58245
>>>        * c-c++-common/pr58245-1.c: New test.
>>>        * g++.dg/pr58245-1.C: Likewise.
>>>        * g++.dg/fstack-protector-strong.C: Adjusted.
>> But is this really something we want?   I'd actually lean towards
>> eliminating the useless load -- I don't necessarily think we should be
>> treating non-returning paths specially here.
>>
>> The whole point of the stack protector is to prevent the *return* path
>> from going to an attacker controlled location.  I'm not sure checking
>> the protector at this point actually does anything particularly useful.
> throw is marked no return.   Since the unwind library may read
> the stack contents to unwind stack, it the stack is corrupted, the
> exception handling may go wrong.   Should we handle this case?
That's the question I think we need to answer.  The EH paths are a known 
security issue on Windows and while ours are notably different I'm not 
sure if there's a real attack surface in those paths.  My sense is that 
if we need to tackle this that doing so on the throw side might be 
better as it's closer conceptually to when//how we check the canary for 
a normal return.

jeff
>
>   --
> H.J.
H.J. Lu Aug. 3, 2022, 5:27 p.m. UTC | #4 
On Tue, Aug 2, 2022 at 4:34 PM Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
>
> On 8/2/2022 11:43 AM, H.J. Lu wrote:
> > On Sat, Jul 30, 2022 at 1:30 PM Jeff Law via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >>
> >> On 7/14/2022 3:55 PM, H.J. Lu via Gcc-patches wrote:
> >>> Check stack canary for noreturn function to catch stack corruption
> >>> before calling noreturn function.  For C++, check stack canary when
> >>> throwing exception or resuming stack unwind to avoid corrupted stack.
> >>>
> >>> gcc/
> >>>
> >>>        PR middle-end/58245
> >>>        * calls.cc (expand_call): Check stack canary for noreturn
> >>>        function.
> >>>
> >>> gcc/testsuite/
> >>>
> >>>        PR middle-end/58245
> >>>        * c-c++-common/pr58245-1.c: New test.
> >>>        * g++.dg/pr58245-1.C: Likewise.
> >>>        * g++.dg/fstack-protector-strong.C: Adjusted.
> >> But is this really something we want?   I'd actually lean towards
> >> eliminating the useless load -- I don't necessarily think we should be
> >> treating non-returning paths specially here.
> >>
> >> The whole point of the stack protector is to prevent the *return* path
> >> from going to an attacker controlled location.  I'm not sure checking
> >> the protector at this point actually does anything particularly useful.
> > throw is marked no return.   Since the unwind library may read
> > the stack contents to unwind stack, it the stack is corrupted, the
> > exception handling may go wrong.   Should we handle this case?
> That's the question I think we need to answer.  The EH paths are a known
> security issue on Windows and while ours are notably different I'm not
> sure if there's a real attack surface in those paths.  My sense is that
> if we need to tackle this that doing so on the throw side might be
> better as it's closer conceptually to when//how we check the canary for
> a normal return.

Like this?

@@ -3154,7 +3155,10 @@ expand_call (tree exp, rtx target, int ignore)
       if (pass && (flags & ECF_MALLOC))
   start_sequence ();

-      if (pass == 0
+      /* Check the canary value for sibcall or function which doesn't
+   return and could throw.  */
+      if ((pass == 0
+     || ((flags & ECF_NORETURN) != 0 && tree_could_throw_p (exp)))
     && crtl->stack_protect_guard
     && targetm.stack_protect_runtime_enabled_p ())
   stack_protect_epilogue ();

> jeff
> >
> >   --
> > H.J.
>
H.J. Lu Aug. 17, 2022, 10:19 p.m. UTC | #5 
On Wed, Aug 3, 2022 at 10:27 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, Aug 2, 2022 at 4:34 PM Jeff Law <jeffreyalaw@gmail.com> wrote:
> >
> >
> >
> > On 8/2/2022 11:43 AM, H.J. Lu wrote:
> > > On Sat, Jul 30, 2022 at 1:30 PM Jeff Law via Gcc-patches
> > > <gcc-patches@gcc.gnu.org> wrote:
> > >>
> > >>
> > >> On 7/14/2022 3:55 PM, H.J. Lu via Gcc-patches wrote:
> > >>> Check stack canary for noreturn function to catch stack corruption
> > >>> before calling noreturn function.  For C++, check stack canary when
> > >>> throwing exception or resuming stack unwind to avoid corrupted stack.
> > >>>
> > >>> gcc/
> > >>>
> > >>>        PR middle-end/58245
> > >>>        * calls.cc (expand_call): Check stack canary for noreturn
> > >>>        function.
> > >>>
> > >>> gcc/testsuite/
> > >>>
> > >>>        PR middle-end/58245
> > >>>        * c-c++-common/pr58245-1.c: New test.
> > >>>        * g++.dg/pr58245-1.C: Likewise.
> > >>>        * g++.dg/fstack-protector-strong.C: Adjusted.
> > >> But is this really something we want?   I'd actually lean towards
> > >> eliminating the useless load -- I don't necessarily think we should be
> > >> treating non-returning paths specially here.
> > >>
> > >> The whole point of the stack protector is to prevent the *return* path
> > >> from going to an attacker controlled location.  I'm not sure checking
> > >> the protector at this point actually does anything particularly useful.
> > > throw is marked no return.   Since the unwind library may read
> > > the stack contents to unwind stack, it the stack is corrupted, the
> > > exception handling may go wrong.   Should we handle this case?
> > That's the question I think we need to answer.  The EH paths are a known
> > security issue on Windows and while ours are notably different I'm not
> > sure if there's a real attack surface in those paths.  My sense is that
> > if we need to tackle this that doing so on the throw side might be
> > better as it's closer conceptually to when//how we check the canary for
> > a normal return.
>
> Like this?
>
> @@ -3154,7 +3155,10 @@ expand_call (tree exp, rtx target, int ignore)
>        if (pass && (flags & ECF_MALLOC))
>    start_sequence ();
>
> -      if (pass == 0
> +      /* Check the canary value for sibcall or function which doesn't
> +   return and could throw.  */
> +      if ((pass == 0
> +     || ((flags & ECF_NORETURN) != 0 && tree_could_throw_p (exp)))
>      && crtl->stack_protect_guard
>      && targetm.stack_protect_runtime_enabled_p ())
>    stack_protect_epilogue ();

Here is the patch:

https://gcc.gnu.org/pipermail/gcc-patches/2022-August/599916.html

> > jeff
> > >
> > >   --
> > > H.J.
> >
>
>
> --
> H.J.
diff mbox series

Patch

diff --git a/gcc/calls.cc b/gcc/calls.cc
index bc96aff38f0..7816c2c8d99 100644
--- a/gcc/calls.cc
+++ b/gcc/calls.cc
@@ -3154,7 +3154,12 @@  expand_call (tree exp, rtx target, int ignore)
       if (pass && (flags & ECF_MALLOC))
 	start_sequence ();
 
-      if (pass == 0
+      /* Check the canary value for sibcall or function which doesn't
+	 return.  */
+      if ((pass == 0
+	   || ((flags & ECF_NORETURN) != 0
+	       && (fndecl
+		   != get_callee_fndecl (targetm.stack_protect_fail ()))))
 	  && crtl->stack_protect_guard
 	  && targetm.stack_protect_runtime_enabled_p ())
 	stack_protect_epilogue ();
diff --git a/gcc/testsuite/c-c++-common/pr58245-1.c b/gcc/testsuite/c-c++-common/pr58245-1.c
new file mode 100644
index 00000000000..945acc53004
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr58245-1.c
@@ -0,0 +1,12 @@ 
+/* { dg-do compile { target i?86-*-* x86_64-*-* rs6000-*-* s390x-*-* } } */
+/* { dg-options "-O2 -fstack-protector-all" } */
+
+extern void foo (void) __attribute__ ((noreturn));
+
+void
+bar (void)
+{
+  foo ();
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 1 } } */
diff --git a/gcc/testsuite/g++.dg/fstack-protector-strong.C b/gcc/testsuite/g++.dg/fstack-protector-strong.C
index ae6d2fdb8df..034af2ce9ab 100644
--- a/gcc/testsuite/g++.dg/fstack-protector-strong.C
+++ b/gcc/testsuite/g++.dg/fstack-protector-strong.C
@@ -85,4 +85,4 @@  int foo7 (B *p)
   return p->return_slot ().a1;
 }
 
-/* { dg-final { scan-assembler-times "stack_chk_fail" 7 } } */
+/* { dg-final { scan-assembler-times "stack_chk_fail" 8 } } */
diff --git a/gcc/testsuite/g++.dg/pr58245-1.C b/gcc/testsuite/g++.dg/pr58245-1.C
new file mode 100644
index 00000000000..1439bc62e71
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr58245-1.C
@@ -0,0 +1,10 @@ 
+/* { dg-do compile { target i?86-*-* x86_64-*-* rs6000-*-* s390x-*-* } } */
+/* { dg-options "-O2 -fstack-protector-all" } */
+
+void
+bar (void)
+{
+  throw 1;
+}
+
+/* { dg-final { scan-assembler-times "stack_chk_fail" 1 } } */