Re: [PATCH] stack-protector: Check stack canary for noreturn function
On Wed, Aug 3, 2022 at 10:27 AM H.J. Lu wrote: > > On Tue, Aug 2, 2022 at 4:34 PM Jeff Law 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 > > > 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. -- H.J.
Re: [PATCH] stack-protector: Check stack canary for noreturn function
On Tue, Aug 2, 2022 at 4:34 PM Jeff Law 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 > > 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.
Re: [PATCH] stack-protector: Check stack canary for noreturn function
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 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.
Re: [PATCH] stack-protector: Check stack canary for noreturn function
On Sat, Jul 30, 2022 at 1:30 PM Jeff Law via Gcc-patches 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.
Re: [PATCH] stack-protector: Check stack canary for noreturn function
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
[PATCH] stack-protector: Check stack canary for noreturn function
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
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 000..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 000..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 } } */
--
2.36.1
