From 43c84e463426ca35fe9fc2d38063d75fed944f23 Mon Sep 17 00:00:00 2001 From: Simon Tatham Date: Mon, 27 Jun 2022 09:36:20 +0100 Subject: [PATCH] [libunwind,EHABI,ARM] Fix get/set of RA_AUTH_CODE. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit According to EHABI32 §8.5.2, the PAC for the return address of a function described in an exception table is supposed to be addressed in the _Unwind_VRS_{Get,Set} API by setting regclass=_UVRSC_PSEUDO and regno=0. (The space of 'regno' values is independent for each regclass, and for _UVRSC_PSEUDO, there is only one valid regno so far.) That is indeed what libunwind's _Unwind_VRS_{Get,Set} functions expect to receive. But at two call sites, the wrong values are passed in: regno is being set to UNW_ARM_RA_AUTH_CODE (0x8F) instead of 0, and in one case, regclass is _UVRSC_CORE instead of _UVRSC_PSEUDO. As a result, those calls to _Unwind_VRS_{Get,Set} return _UVRSR_FAILED, which their callers ignore. So if you compile in the AUTG instruction that actually validates the PAC, it will try to validate what's effectively an uninitialised register as an authentication code, and trigger a CPU fault even on correct exception unwinding. Reviewed By: danielkiss Differential Revision: https://reviews.llvm.org/D128522 --- libunwind/src/Unwind-EHABI.cpp | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/libunwind/src/Unwind-EHABI.cpp b/libunwind/src/Unwind-EHABI.cpp index 6ac09ad..f203887 100644 --- a/libunwind/src/Unwind-EHABI.cpp +++ b/libunwind/src/Unwind-EHABI.cpp @@ -432,8 +432,7 @@ _Unwind_VRS_Interpret(_Unwind_Context *context, const uint32_t *data, uint32_t sp; uint32_t pac; _Unwind_VRS_Get(context, _UVRSC_CORE, UNW_ARM_SP, _UVRSD_UINT32, &sp); - _Unwind_VRS_Get(context, _UVRSC_PSEUDO, UNW_ARM_RA_AUTH_CODE, - _UVRSD_UINT32, &pac); + _Unwind_VRS_Get(context, _UVRSC_PSEUDO, 0, _UVRSD_UINT32, &pac); __asm__ __volatile__("autg %0, %1, %2" : : "r"(pac), "r"(lr), "r"(sp) :); } #else @@ -1138,8 +1137,7 @@ _Unwind_VRS_Pop(_Unwind_Context *context, _Unwind_VRS_RegClass regclass, } uint32_t pac = *sp++; _Unwind_VRS_Set(context, _UVRSC_CORE, UNW_ARM_SP, _UVRSD_UINT32, &sp); - return _Unwind_VRS_Set(context, _UVRSC_CORE, UNW_ARM_RA_AUTH_CODE, - _UVRSD_UINT32, &pac); + return _Unwind_VRS_Set(context, _UVRSC_PSEUDO, 0, _UVRSD_UINT32, &pac); } } _LIBUNWIND_ABORT("unsupported register class"); -- 2.7.4