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[libunwind] Add GCS support for AArch64 #99335

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merged 4 commits into from
Aug 4, 2024
Merged

[libunwind] Add GCS support for AArch64 #99335

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e0f7186
[libunwind] Add GCS support for AArch64
john-brawn-arm Jul 17, 2024
c9f7373
Adjust _LIBUNWIND_POP_CET_SSP
john-brawn-arm Jul 19, 2024
bb7ade6
Add _LIBUNWIND_USE_GCS instead of re-using _LIBUNWIND_USE_CET
john-brawn-arm Jul 19, 2024
c776eaf
Remove braces, adjust comments
john-brawn-arm Aug 4, 2024
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8 changes: 8 additions & 0 deletions libunwind/CMakeLists.txt
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Expand Up @@ -37,6 +37,7 @@ if (LIBUNWIND_BUILD_32_BITS)
endif()

option(LIBUNWIND_ENABLE_CET "Build libunwind with CET enabled." OFF)
option(LIBUNWIND_ENABLE_GCS "Build libunwind with GCS enabled." OFF)
option(LIBUNWIND_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
option(LIBUNWIND_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
option(LIBUNWIND_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
Expand Down Expand Up @@ -188,6 +189,13 @@ if (LIBUNWIND_ENABLE_CET)
endif()
endif()

if (LIBUNWIND_ENABLE_GCS)
add_compile_flags_if_supported(-mbranch-protection=standard)
if (NOT CXX_SUPPORTS_MBRANCH_PROTECTION_EQ_STANDARD_FLAG)
message(SEND_ERROR "Compiler doesn't support GCS -mbranch-protection option!")
endif()
endif()

if (WIN32)
# The headers lack matching dllexport attributes (_LIBUNWIND_EXPORT);
# silence the warning instead of cluttering the headers (which aren't
Expand Down
7 changes: 7 additions & 0 deletions libunwind/src/Registers.hpp
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Expand Up @@ -1815,6 +1815,13 @@ inline const char *Registers_ppc64::getRegisterName(int regNum) {
/// process.
class _LIBUNWIND_HIDDEN Registers_arm64;
extern "C" void __libunwind_Registers_arm64_jumpto(Registers_arm64 *);

#if defined(_LIBUNWIND_USE_GCS)
extern "C" void *__libunwind_cet_get_jump_target() {
return reinterpret_cast<void *>(&__libunwind_Registers_arm64_jumpto);
}
#endif

class _LIBUNWIND_HIDDEN Registers_arm64 {
public:
Registers_arm64();
Expand Down
6 changes: 3 additions & 3 deletions libunwind/src/UnwindCursor.hpp
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Expand Up @@ -471,7 +471,7 @@ class _LIBUNWIND_HIDDEN AbstractUnwindCursor {
}
#endif

#if defined(_LIBUNWIND_USE_CET)
#if defined(_LIBUNWIND_USE_CET) || defined(_LIBUNWIND_USE_GCS)
virtual void *get_registers() {
_LIBUNWIND_ABORT("get_registers not implemented");
}
Expand Down Expand Up @@ -954,7 +954,7 @@ class UnwindCursor : public AbstractUnwindCursor{
virtual uintptr_t getDataRelBase();
#endif

#if defined(_LIBUNWIND_USE_CET)
#if defined(_LIBUNWIND_USE_CET) || defined(_LIBUNWIND_USE_GCS)
virtual void *get_registers() { return &_registers; }
#endif

Expand Down Expand Up @@ -3004,7 +3004,7 @@ bool UnwindCursor<A, R>::isReadableAddr(const pint_t addr) const {
}
#endif

#if defined(_LIBUNWIND_USE_CET)
#if defined(_LIBUNWIND_USE_CET) || defined(_LIBUNWIND_USE_GCS)
extern "C" void *__libunwind_cet_get_registers(unw_cursor_t *cursor) {
AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
return co->get_registers();
Expand Down
32 changes: 29 additions & 3 deletions libunwind/src/UnwindLevel1.c
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Expand Up @@ -44,7 +44,7 @@
// _LIBUNWIND_POP_CET_SSP is used to adjust CET shadow stack pointer and we
// directly jump to __libunwind_Registers_x86/x86_64_jumpto instead of using
// a regular function call to avoid pushing to CET shadow stack again.
#if !defined(_LIBUNWIND_USE_CET)
#if !defined(_LIBUNWIND_USE_CET) && !defined(_LIBUNWIND_USE_GCS)
#define __unw_phase2_resume(cursor, fn) \
do { \
(void)fn; \
Expand Down Expand Up @@ -72,6 +72,19 @@
__asm__ volatile("jmpq *%%rdx\n\t" :: "D"(cetRegContext), \
"d"(cetJumpAddress)); \
} while (0)
#elif defined(_LIBUNWIND_TARGET_AARCH64)
#define __cet_ss_step_size 8
#define __unw_phase2_resume(cursor, fn) \
do { \
_LIBUNWIND_POP_CET_SSP((fn)); \
void *cetRegContext = __libunwind_cet_get_registers((cursor)); \
void *cetJumpAddress = __libunwind_cet_get_jump_target(); \
__asm__ volatile("mov x0, %0\n\t" \
"br %1\n\t" \
: \
: "r"(cetRegContext), "r"(cetJumpAddress) \
: "x0"); \
} while (0)
#endif

static _Unwind_Reason_Code
Expand Down Expand Up @@ -170,6 +183,10 @@ unwind_phase1(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *except
}
extern int __unw_step_stage2(unw_cursor_t *);

#if defined(_LIBUNWIND_USE_GCS)
// Enable the GCS target feature to permit GCS instructions to be used.
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Might be useful to elaborate what instructions need to use the GCS version.

__attribute__((target("gcs")))
#endif
static _Unwind_Reason_Code
unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *exception_object) {
__unw_init_local(cursor, uc);
Expand All @@ -180,8 +197,13 @@ unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *except
// uc is initialized by __unw_getcontext in the parent frame. The first stack
// frame walked is unwind_phase2.
unsigned framesWalked = 1;
#ifdef _LIBUNWIND_USE_CET
#if defined(_LIBUNWIND_USE_CET)
unsigned long shadowStackTop = _get_ssp();
#elif defined(_LIBUNWIND_USE_GCS)
unsigned long shadowStackTop = 0;
if (__chkfeat(_CHKFEAT_GCS)) {
shadowStackTop = (unsigned long)__gcspr();
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the brace can be dropped

}
#endif
// Walk each frame until we reach where search phase said to stop.
while (true) {
Expand Down Expand Up @@ -238,7 +260,7 @@ unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *except
// against return address stored in CET shadow stack, if the 2 addresses don't
// match, it means return address in normal stack has been corrupted, we return
// _URC_FATAL_PHASE2_ERROR.
#ifdef _LIBUNWIND_USE_CET
#if defined(_LIBUNWIND_USE_CET) || defined(_LIBUNWIND_USE_GCS)
if (shadowStackTop != 0) {
unw_word_t retInNormalStack;
__unw_get_reg(cursor, UNW_REG_IP, &retInNormalStack);
Expand Down Expand Up @@ -306,6 +328,10 @@ unwind_phase2(unw_context_t *uc, unw_cursor_t *cursor, _Unwind_Exception *except
return _URC_FATAL_PHASE2_ERROR;
}

#if defined(_LIBUNWIND_USE_GCS)
// Enable the GCS target feature to permit GCS instructions to be used.
__attribute__((target("gcs")))
#endif
static _Unwind_Reason_Code
unwind_phase2_forced(unw_context_t *uc, unw_cursor_t *cursor,
_Unwind_Exception *exception_object,
Expand Down
2 changes: 1 addition & 1 deletion libunwind/src/UnwindRegistersRestore.S
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Expand Up @@ -680,7 +680,7 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_arm64_jumpto)
ldr x16, [x0, #0x0F8]
ldp x0, x1, [x0, #0x000] // restore x0,x1
mov sp,x16 // restore sp
ret x30 // jump to pc
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If the application is compiled with BTI then br x30 will cause an exception as it jumps to a non landing pad instruction.
(We only generate landing pads for return-twice locations but a normal catch block won't get it)

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Yes you're right, and actually the way I've adjusted __unw_phase2_resume also means we need to change the BTI instruction in __libunwind_Registers_arm64_jumpto to BTI JC. I'll fix this.

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#102322 should fix this

br x30 // jump to pc

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

Expand Down
18 changes: 18 additions & 0 deletions libunwind/src/cet_unwind.h
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Expand Up @@ -35,6 +35,24 @@
} while (0)
#endif

// On AArch64 we use _LIBUNWIND_USE_GCS to indicate that GCS is supported. We
// need to guard any use of GCS instructions with __chkfeat though, as GCS may
// not be enabled.
#if defined(_LIBUNWIND_TARGET_AARCH64) && defined(__ARM_FEATURE_GCS_DEFAULT)
#define _LIBUNWIND_USE_GCS 1
#include <arm_acle.h>

#define _LIBUNWIND_POP_CET_SSP(x) \
do { \
if (__chkfeat(_CHKFEAT_GCS)) { \
unsigned tmp = (x); \
while (tmp--) \
__gcspopm(); \
} \
} while (0)

#endif

extern void *__libunwind_cet_get_registers(unw_cursor_t *);
extern void *__libunwind_cet_get_jump_target(void);

Expand Down
1 change: 1 addition & 0 deletions libunwind/test/CMakeLists.txt
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Expand Up @@ -9,6 +9,7 @@ macro(pythonize_bool var)
endmacro()

pythonize_bool(LIBUNWIND_ENABLE_CET)
pythonize_bool(LIBUNWIND_ENABLE_GCS)
pythonize_bool(LIBUNWIND_ENABLE_THREADS)
pythonize_bool(LIBUNWIND_USES_ARM_EHABI)

Expand Down
3 changes: 3 additions & 0 deletions libunwind/test/configs/llvm-libunwind-merged.cfg.in
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Expand Up @@ -11,6 +11,9 @@ link_flags = []
if @LIBUNWIND_ENABLE_CET@:
compile_flags.append('-fcf-protection=full')

if @LIBUNWIND_ENABLE_GCS@:
compile_flags.append('-mbranch-protection=standard')

# On ELF platforms, link tests with -Wl,--export-dynamic if supported by the linker.
if len('@CMAKE_EXE_EXPORTS_CXX_FLAG@'):
link_flags.append('@CMAKE_EXE_EXPORTS_CXX_FLAG@')
Expand Down
3 changes: 3 additions & 0 deletions libunwind/test/configs/llvm-libunwind-shared.cfg.in
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Expand Up @@ -10,6 +10,9 @@ link_flags = []
if @LIBUNWIND_ENABLE_CET@:
compile_flags.append('-fcf-protection=full')

if @LIBUNWIND_ENABLE_GCS@:
compile_flags.append('-mbranch-protection=standard')

# On ELF platforms, link tests with -Wl,--export-dynamic if supported by the linker.
if len('@CMAKE_EXE_EXPORTS_CXX_FLAG@'):
link_flags.append('@CMAKE_EXE_EXPORTS_CXX_FLAG@')
Expand Down
3 changes: 3 additions & 0 deletions libunwind/test/configs/llvm-libunwind-static.cfg.in
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Expand Up @@ -13,6 +13,9 @@ if @LIBUNWIND_ENABLE_THREADS@:
if @LIBUNWIND_ENABLE_CET@:
compile_flags.append('-fcf-protection=full')

if @LIBUNWIND_ENABLE_GCS@:
compile_flags.append('-mbranch-protection=standard')

# On ELF platforms, link tests with -Wl,--export-dynamic if supported by the linker.
if len('@CMAKE_EXE_EXPORTS_CXX_FLAG@'):
link_flags.append('@CMAKE_EXE_EXPORTS_CXX_FLAG@')
Expand Down
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