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[libunwind] Fix problems caused by combining BTI and GCS #102322

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Merged
merged 2 commits into from
Aug 8, 2024
Merged

[libunwind] Fix problems caused by combining BTI and GCS #102322

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1c6cbe6
[libunwind] Fix problems caused by combining BTI and GCS
john-brawn-arm Aug 7, 2024
d642414
Update libunwind/src/UnwindRegistersRestore.S
john-brawn-arm Aug 7, 2024
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16 changes: 15 additions & 1 deletion libunwind/src/UnwindRegistersRestore.S
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Original file line number Diff line number Diff line change
Expand Up @@ -629,6 +629,10 @@ Lnovec:

#elif defined(__aarch64__)

#if defined(__ARM_FEATURE_GCS_DEFAULT)
.arch_extension gcs
#endif

//
// extern "C" void __libunwind_Registers_arm64_jumpto(Registers_arm64 *);
//
Expand Down Expand Up @@ -680,7 +684,17 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_arm64_jumpto)
ldr x16, [x0, #0x0F8]
ldp x0, x1, [x0, #0x000] // restore x0,x1
mov sp,x16 // restore sp
br x30 // jump to pc
#if defined(__ARM_FEATURE_GCS_DEFAULT)
// If GCS is enabled we need to push the address we're returning to onto the
// GCS stack. We can't just return using br, as there won't be a BTI landing
// pad instruction at the destination.
mov x16, #1
chkfeat x16
cbnz x16, Lnogcs
gcspushm x30
Lnogcs:
#endif
ret x30 // jump to pc

#elif defined(__arm__) && !defined(__APPLE__)

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25 changes: 20 additions & 5 deletions libunwind/src/assembly.h
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Expand Up @@ -82,7 +82,22 @@
#define PPC64_OPD2
#endif

#if defined(__aarch64__) && defined(__ARM_FEATURE_BTI_DEFAULT)
#if defined(__aarch64__)
#if defined(__ARM_FEATURE_GCS_DEFAULT) && defined(__ARM_FEATURE_BTI_DEFAULT)
// Set BTI, PAC, and GCS gnu property bits
#define GNU_PROPERTY 7
// We indirectly branch to __libunwind_Registers_arm64_jumpto from
// __unw_phase2_resume, so we need to use bti jc.
#define AARCH64_BTI bti jc
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__unw_getcontext will also get the bti jc so slightly weakens the BTI protection but since paciasp is also bti jc might not be a big problem.

#elif defined(__ARM_FEATURE_GCS_DEFAULT)
// Set GCS gnu property bit
#define GNU_PROPERTY 4
#elif defined(__ARM_FEATURE_BTI_DEFAULT)
// Set BTI and PAC gnu property bits
#define GNU_PROPERTY 3
#define AARCH64_BTI bti c
#endif
#ifdef GNU_PROPERTY
.pushsection ".note.gnu.property", "a" SEPARATOR \
.balign 8 SEPARATOR \
.long 4 SEPARATOR \
Expand All @@ -91,12 +106,12 @@
.asciz "GNU" SEPARATOR \
.long 0xc0000000 SEPARATOR /* GNU_PROPERTY_AARCH64_FEATURE_1_AND */ \
.long 4 SEPARATOR \
.long 3 SEPARATOR /* GNU_PROPERTY_AARCH64_FEATURE_1_BTI AND */ \
/* GNU_PROPERTY_AARCH64_FEATURE_1_PAC */ \
.long GNU_PROPERTY SEPARATOR \
.long 0 SEPARATOR \
.popsection SEPARATOR
#define AARCH64_BTI bti c
#else
#endif
#endif
#if !defined(AARCH64_BTI)
#define AARCH64_BTI
#endif

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