diff --git a/libgcc/config/aarch64/aarch64-unwind.h b/libgcc/config/aarch64/aarch64-unwind.h index 4d36f0b26f70385522d08df7e36fa177f7ea7b62..cf4ec749c0552412409133fa225c9fb59252211d 100644 --- a/libgcc/config/aarch64/aarch64-unwind.h +++ b/libgcc/config/aarch64/aarch64-unwind.h @@ -178,6 +178,9 @@ aarch64_demangle_return_addr (struct _Unwind_Context *context, return addr; } +/* GCS enable flag for chkfeat instruction. */ +#define CHKFEAT_GCS 1 + /* SME runtime function local to libgcc, streaming compatible and preserves more registers than the base PCS requires, but we don't rely on that here. */ @@ -185,12 +188,66 @@ __attribute__ ((visibility ("hidden"))) void __libgcc_arm_za_disable (void); /* Disable the SME ZA state in case an unwound frame used the ZA - lazy saving scheme. */ + lazy saving scheme. And unwind the GCS for EH. */ #undef _Unwind_Frames_Extra #define _Unwind_Frames_Extra(x) \ do \ { \ __libgcc_arm_za_disable (); \ + if (__builtin_aarch64_chkfeat (CHKFEAT_GCS) == 0) \ + { \ + for (_Unwind_Word n = (x); n != 0; n--) \ + __builtin_aarch64_gcspopm (); \ + } \ + } \ + while (0) + +/* On signal entry the OS places a token on the GCS that can be used to + verify the integrity of the GCS pointer on signal return. It also + places the signal handler return address (the restorer that calls the + signal return syscall) on the GCS so the handler can return. + Because of this token, each stack frame visited during unwinding has + exactly one corresponding entry on the GCS, so the frame count is + the number of entries that will have to be popped at EH return time. + + Note: This depends on the GCS signal ABI of the OS. + + When unwinding across a stack frame for each frame the corresponding + entry is checked on the GCS against the computed return address from + the normal stack. If they don't match then _URC_FATAL_PHASE2_ERROR + is returned. This check is omitted if + + 1. GCS is disabled. Note: asynchronous GCS disable is supported here + if GCSPR and the GCS remains readable. + 2. Non-catchable exception where exception_class == 0. Note: the + pthread cancellation implementation in glibc sets exception_class + to 0 when the unwinder is used for cancellation cleanup handling, + so this allows the GCS to get out of sync during cancellation. + This weakens security but avoids an ABI break in glibc. + 3. Zero return address which marks the outermost stack frame. + 4. Signal stack frame, the GCS entry is an OS specific token then + with the top bit set. + */ +#undef _Unwind_Frames_Increment +#define _Unwind_Frames_Increment(exc, context, frames) \ + do \ + { \ + frames++; \ + if (__builtin_aarch64_chkfeat (CHKFEAT_GCS) != 0 \ + || exc->exception_class == 0 \ + || _Unwind_GetIP (context) == 0) \ + break; \ + const _Unwind_Word *gcs = __builtin_aarch64_gcspr (); \ + if (_Unwind_IsSignalFrame (context)) \ + { \ + if (gcs[frames] >> 63 == 0) \ + return _URC_FATAL_PHASE2_ERROR; \ + } \ + else \ + { \ + if (gcs[frames] != _Unwind_GetIP (context)) \ + return _URC_FATAL_PHASE2_ERROR; \ + } \ } \ while (0)