diff options
| author | Ard Biesheuvel <ardb@kernel.org> | 2022-10-27 17:59:08 +0200 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2022-11-09 18:06:35 +0000 |
| commit | 3b619e22c4601b444ed2d6a5458271f72625ac89 (patch) | |
| tree | 1f4754b78c6302a14322f629b72a6f195d8dd58e /arch/arm64/include | |
| parent | 9beccca0984022a844850e32f0d7dd80d4a225de (diff) | |
arm64: implement dynamic shadow call stack for Clang
Implement dynamic shadow call stack support on Clang, by parsing the
unwind tables at init time to locate all occurrences of PACIASP/AUTIASP
instructions, and replacing them with the shadow call stack push and pop
instructions, respectively.
This is useful because the overhead of the shadow call stack is
difficult to justify on hardware that implements pointer authentication
(PAC), and given that the PAC instructions are executed as NOPs on
hardware that doesn't, we can just replace them without breaking
anything. As PACIASP/AUTIASP are guaranteed to be paired with respect to
manipulations of the return address, replacing them 1:1 with shadow call
stack pushes and pops is guaranteed to result in the desired behavior.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20221027155908.1940624-4-ardb@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/include')
| -rw-r--r-- | arch/arm64/include/asm/scs.h | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h index 8297bccf0784..ff7da1268a52 100644 --- a/arch/arm64/include/asm/scs.h +++ b/arch/arm64/include/asm/scs.h @@ -5,6 +5,7 @@ #ifdef __ASSEMBLY__ #include <asm/asm-offsets.h> +#include <asm/sysreg.h> #ifdef CONFIG_SHADOW_CALL_STACK scs_sp .req x18 @@ -24,6 +25,54 @@ .endm #endif /* CONFIG_SHADOW_CALL_STACK */ + +#else + +#include <linux/scs.h> +#include <asm/cpufeature.h> + +#ifdef CONFIG_UNWIND_PATCH_PAC_INTO_SCS +static inline bool should_patch_pac_into_scs(void) +{ + u64 reg; + + /* + * We only enable the shadow call stack dynamically if we are running + * on a system that does not implement PAC or BTI. PAC and SCS provide + * roughly the same level of protection, and BTI relies on the PACIASP + * instructions serving as landing pads, preventing us from patching + * those instructions into something else. + */ + reg = read_sysreg_s(SYS_ID_AA64ISAR1_EL1); + if (SYS_FIELD_GET(ID_AA64ISAR1_EL1, APA, reg) | + SYS_FIELD_GET(ID_AA64ISAR1_EL1, API, reg)) + return false; + + reg = read_sysreg_s(SYS_ID_AA64ISAR2_EL1); + if (SYS_FIELD_GET(ID_AA64ISAR2_EL1, APA3, reg)) + return false; + + if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)) { + reg = read_sysreg_s(SYS_ID_AA64PFR1_EL1); + if (reg & (0xf << ID_AA64PFR1_EL1_BT_SHIFT)) + return false; + } + return true; +} + +static inline void dynamic_scs_init(void) +{ + if (should_patch_pac_into_scs()) { + pr_info("Enabling dynamic shadow call stack\n"); + static_branch_enable(&dynamic_scs_enabled); + } +} +#else +static inline void dynamic_scs_init(void) {} +#endif + +int scs_patch(const u8 eh_frame[], int size); + #endif /* __ASSEMBLY __ */ #endif /* _ASM_SCS_H */ |