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x86/cet: Check feature_1 in TCB for active IBT and SHSTK

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Initially, IBT and SHSTK are marked as active when CPU supports them
and CET are enabled in glibc.  They can be disabled early by tunables
before relocation.  Since after relocation, GLRO(dl_x86_cpu_features)
becomes read-only, we can't update GLRO(dl_x86_cpu_features) to mark
IBT and SHSTK as inactive.  Instead, check the feature_1 field in TCB
to decide if IBT and SHST are active.
This commit is contained in:
H.J. Lu 2023-12-29 08:43:52 -08:00
parent 541641a3de
commit d360dcc001
3 changed files with 35 additions and 1 deletions
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8
sysdeps/x86/bits/platform/x86.h
View File

@ -337,3 +337,11 @@ enum
x86_cpu_AVX10_YMM = x86_cpu_index_24_ecx_0_ebx + 17,
x86_cpu_AVX10_ZMM = x86_cpu_index_24_ecx_0_ebx + 18,
};
/* Bits in the feature_1 field in TCB. */
enum
{
x86_feature_1_ibt = 1U << 0,
x86_feature_1_shstk = 1U << 1
};

11
sysdeps/x86/get-cpuid-feature-leaf.c
View File

@ -15,9 +15,18 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <assert.h>
#include <tcb-offsets.h>
#include <ldsodefs.h>
#ifdef __x86_64__
# ifdef __LP64__
_Static_assert (FEATURE_1_OFFSET == 72, "FEATURE_1_OFFSET != 72");
# else
_Static_assert (FEATURE_1_OFFSET == 40, "FEATURE_1_OFFSET != 40");
# endif
#endif
const struct cpuid_feature *
__x86_get_cpuid_feature_leaf (unsigned int leaf)
{

17
sysdeps/x86/sys/platform/x86.h
View File

@ -45,6 +45,23 @@ x86_cpu_present (unsigned int __index)
static __inline__ _Bool
x86_cpu_active (unsigned int __index)
{
if (__index == x86_cpu_IBT || __index == x86_cpu_SHSTK)
{
#ifdef __x86_64__
unsigned int __feature_1;
# ifdef __LP64__
__asm__ ("mov %%fs:72, %0" : "=r" (__feature_1));
# else
__asm__ ("mov %%fs:40, %0" : "=r" (__feature_1));
# endif
if (__index == x86_cpu_IBT)
return __feature_1 & x86_feature_1_ibt;
else
return __feature_1 & x86_feature_1_shstk;
#else
return false;
#endif
}
const struct cpuid_feature *__ptr = __x86_get_cpuid_feature_leaf
(__index / (8 * sizeof (unsigned int) * 4));
unsigned int __reg