From ec0288369f0cc6d85837a18f1c4c65451c94477b Mon Sep 17 00:00:00 2001 From: Vincenzo Frascino Date: Wed, 6 Oct 2021 16:47:50 +0100 Subject: arm64: mte: Add asymmetric mode support MTE provides an asymmetric mode for detecting tag exceptions. In particular, when such a mode is present, the CPU triggers a fault on a tag mismatch during a load operation and asynchronously updates a register when a tag mismatch is detected during a store operation. Add support for MTE asymmetric mode. Note: If the CPU does not support MTE asymmetric mode the kernel falls back on synchronous mode which is the default for kasan=on. Cc: Will Deacon Cc: Catalin Marinas Cc: Andrey Konovalov Signed-off-by: Vincenzo Frascino Reviewed-by: Catalin Marinas Acked-by: Andrey Konovalov Link: https://lore.kernel.org/r/20211006154751.4463-5-vincenzo.frascino@arm.com Signed-off-by: Will Deacon --- arch/arm64/include/asm/memory.h | 1 + arch/arm64/include/asm/mte-kasan.h | 5 +++++ arch/arm64/include/asm/mte.h | 8 ++++---- arch/arm64/include/asm/uaccess.h | 4 ++-- arch/arm64/kernel/mte.c | 41 ++++++++++++++++++++++++++++++++------ 5 files changed, 47 insertions(+), 12 deletions(-) diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index f1745a843414..1b9a1e242612 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -243,6 +243,7 @@ static inline const void *__tag_set(const void *addr, u8 tag) #ifdef CONFIG_KASAN_HW_TAGS #define arch_enable_tagging_sync() mte_enable_kernel_sync() #define arch_enable_tagging_async() mte_enable_kernel_async() +#define arch_enable_tagging_asymm() mte_enable_kernel_asymm() #define arch_force_async_tag_fault() mte_check_tfsr_exit() #define arch_get_random_tag() mte_get_random_tag() #define arch_get_mem_tag(addr) mte_get_mem_tag(addr) diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h index 22420e1f8c03..478b9bcf69ad 100644 --- a/arch/arm64/include/asm/mte-kasan.h +++ b/arch/arm64/include/asm/mte-kasan.h @@ -130,6 +130,7 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag, void mte_enable_kernel_sync(void); void mte_enable_kernel_async(void); +void mte_enable_kernel_asymm(void); #else /* CONFIG_ARM64_MTE */ @@ -161,6 +162,10 @@ static inline void mte_enable_kernel_async(void) { } +static inline void mte_enable_kernel_asymm(void) +{ +} + #endif /* CONFIG_ARM64_MTE */ #endif /* __ASSEMBLY__ */ diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index 02511650cffe..075539f5f1c8 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -88,11 +88,11 @@ static inline int mte_ptrace_copy_tags(struct task_struct *child, #ifdef CONFIG_KASAN_HW_TAGS /* Whether the MTE asynchronous mode is enabled. */ -DECLARE_STATIC_KEY_FALSE(mte_async_mode); +DECLARE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); -static inline bool system_uses_mte_async_mode(void) +static inline bool system_uses_mte_async_or_asymm_mode(void) { - return static_branch_unlikely(&mte_async_mode); + return static_branch_unlikely(&mte_async_or_asymm_mode); } void mte_check_tfsr_el1(void); @@ -121,7 +121,7 @@ static inline void mte_check_tfsr_exit(void) mte_check_tfsr_el1(); } #else -static inline bool system_uses_mte_async_mode(void) +static inline bool system_uses_mte_async_or_asymm_mode(void) { return false; } diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index 190b494e22ab..315354047d69 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -196,13 +196,13 @@ static inline void __uaccess_enable_tco(void) */ static inline void __uaccess_disable_tco_async(void) { - if (system_uses_mte_async_mode()) + if (system_uses_mte_async_or_asymm_mode()) __uaccess_disable_tco(); } static inline void __uaccess_enable_tco_async(void) { - if (system_uses_mte_async_mode()) + if (system_uses_mte_async_or_asymm_mode()) __uaccess_enable_tco(); } diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index 0cdae086966e..f418ebc65f95 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -26,9 +26,12 @@ static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred); #ifdef CONFIG_KASAN_HW_TAGS -/* Whether the MTE asynchronous mode is enabled. */ -DEFINE_STATIC_KEY_FALSE(mte_async_mode); -EXPORT_SYMBOL_GPL(mte_async_mode); +/* + * The asynchronous and asymmetric MTE modes have the same behavior for + * store operations. This flag is set when either of these modes is enabled. + */ +DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); +EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode); #endif static void mte_sync_page_tags(struct page *page, pte_t old_pte, @@ -116,7 +119,7 @@ void mte_enable_kernel_sync(void) * Make sure we enter this function when no PE has set * async mode previously. */ - WARN_ONCE(system_uses_mte_async_mode(), + WARN_ONCE(system_uses_mte_async_or_asymm_mode(), "MTE async mode enabled system wide!"); __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC); @@ -134,8 +137,34 @@ void mte_enable_kernel_async(void) * mode in between sync and async, this strategy needs * to be reviewed. */ - if (!system_uses_mte_async_mode()) - static_branch_enable(&mte_async_mode); + if (!system_uses_mte_async_or_asymm_mode()) + static_branch_enable(&mte_async_or_asymm_mode); +} + +void mte_enable_kernel_asymm(void) +{ + if (cpus_have_cap(ARM64_MTE_ASYMM)) { + __mte_enable_kernel("asymmetric", SCTLR_ELx_TCF_ASYMM); + + /* + * MTE asymm mode behaves as async mode for store + * operations. The mode is set system wide by the + * first PE that executes this function. + * + * Note: If in future KASAN acquires a runtime switching + * mode in between sync and async, this strategy needs + * to be reviewed. + */ + if (!system_uses_mte_async_or_asymm_mode()) + static_branch_enable(&mte_async_or_asymm_mode); + } else { + /* + * If the CPU does not support MTE asymmetric mode the + * kernel falls back on synchronous mode which is the + * default for kasan=on. + */ + mte_enable_kernel_sync(); + } } #endif -- cgit v1.2.3-59-g8ed1b