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Re: [PATCH 08/12] De-PLTize __stack_chk_fail internal calls within libc.so.
On 15 Dec 2016, Florian Weimer told this:
> On 12/15/2016 03:15 PM, Nix wrote:
>
>> Possible fix, untested:
>>
>> diff --git a/sysdeps/generic/symbol-hacks.h b/sysdeps/generic/symbol-hacks.h
>> index 36908b5..0679354 100644
>> --- a/sysdeps/generic/symbol-hacks.h
>> +++ b/sysdeps/generic/symbol-hacks.h
>> @@ -7,5 +7,7 @@ asm ("memcpy = __GI_memcpy");
>>
>> /* -fstack-protector generates calls to __stack_chk_fail, which need
>> similar adjustments to avoid going through the PLT. */
>> +#if defined __SSP__ || defined __SSP_ALL__ || defined __SSP_STRONG__
>> asm ("__stack_chk_fail = __stack_chk_fail_local");
>> #endif
>> +#endif
>
> The condition looks rather brittle. What if GCC grows an -fstack-protector-light switch and __SSP_LIGHT__ macro?
We'd need to change configure.ac before that would have an effect in any
case... but it does seem likely that changing this too would be
overlooked.
> I wonder if it's better to add something to $(no-stack-protector) and use that in the conditional.
That was my other option, but the total absence of anything in
configure.ac passing -D made me think twice.
Something like this? (even more untested than the last one, if
possible -- but adds a new possibility: we can now differentiate between
"glibc built without stack protector" and "glibc built with stack
protector but this file doesn't have it" without relying on GCC
predefined macros. The __WITH_ naming scheme is completely arbitrary
and I can change it to anything you prefer.)
diff --git a/configure.ac b/configure.ac
index 2396c1f..8bb8c2c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -638,18 +638,18 @@ LIBC_TRY_CC_OPTION([$CFLAGS $CPPFLAGS -Werror -fstack-protector-all],
stack_protector=
no_stack_protector=
if test "$libc_cv_ssp" = yes; then
- no_stack_protector="-fno-stack-protector"
+ no_stack_protector="-fno-stack-protector -D__WITH_STACK_PROTECTOR=0"
AC_DEFINE(HAVE_CC_NO_STACK_PROTECTOR)
fi
if test "$enable_stack_protector" = yes && test "$libc_cv_ssp" = yes; then
- stack_protector="-fstack-protector"
+ stack_protector="-fstack-protector -D__WITH_STACK_PROTECTOR=1"
AC_DEFINE(STACK_PROTECTOR_LEVEL, 1)
elif test "$enable_stack_protector" = all && test "$libc_cv_ssp_all" = yes; then
- stack_protector="-fstack-protector-all"
+ stack_protector="-fstack-protector-all -D__WITH_STACK_PROTECTOR=2"
AC_DEFINE(STACK_PROTECTOR_LEVEL, 2)
elif test "$enable_stack_protector" = strong && test "$libc_cv_ssp_strong" = yes; then
- stack_protector="-fstack-protector-strong"
+ stack_protector="-fstack-protector-strong -D__WITH_STACK_PROTECTOR=3"
AC_DEFINE(STACK_PROTECTOR_LEVEL, 3)
fi
AC_SUBST(libc_cv_ssp)
diff --git a/sysdeps/generic/symbol-hacks.h b/sysdeps/generic/symbol-hacks.h
index 36908b5..12b4fe7 100644
--- a/sysdeps/generic/symbol-hacks.h
+++ b/sysdeps/generic/symbol-hacks.h
@@ -7,5 +7,7 @@ asm ("memcpy = __GI_memcpy");
/* -fstack-protector generates calls to __stack_chk_fail, which need
similar adjustments to avoid going through the PLT. */
+#if defined __WITH_STACK_PROTECTOR && __WITH_STACK_PROTECTOR > 0
asm ("__stack_chk_fail = __stack_chk_fail_local");
#endif
+#endif