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charset="utf-8" Content-Transfer-Encoding: quoted-printable With MTE, the IRG instruction tags a pointer in-place, so that set_tag(ptr, hw_get_random_tag()) can conceptually be synthesized as a single "IRG %[ptr], %[ptr], 0". However, with the way the API is currently defined, we confuse the compiler into generating a random tag with invalid address bits, to then bitfield-extract the tag and shift-and-mask it into another pointer. Furthermore, every single (indirect or direct) use-case for a random tag in arch-agnostic KASAN ends up passing it to set_tag(), which likely is an indicator of a suboptimal API design. Therefore, make the function clearer and more optimization-friendly by directly taking the pointer to be randomly tagged. Update the only definition (in arm64) accordingly. Intentionally keep this patch minimal (and limited to KASAN_HW_TAGS) to reduce its associated risks and make it as uncontentious as possible. A future patch will refactor the arch-agnostic KASAN code to enable the optimization mentioned above. Cc: Alexander Potapenko Cc: Andrew Morton Cc: Andrey Konovalov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: kasan-dev@googlegroups.com Cc: linux-mm@kvack.org Signed-off-by: Pierre-Cl=C3=A9ment Tosi --- arch/arm64/include/asm/memory.h | 2 +- arch/arm64/include/asm/mte-kasan.h | 14 +++++++------- mm/kasan/kasan.h | 7 +++++-- 3 files changed, 13 insertions(+), 10 deletions(-) diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memor= y.h index 8e751b56d20c..29e7537f5e58 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -317,7 +317,7 @@ static inline const void *__tag_set(const void *addr, u= 8 tag) #define arch_suppress_tag_checks_start() mte_enable_tco() #define arch_suppress_tag_checks_stop() mte_disable_tco() #define arch_flush_async_tag_fault() mte_get_reset_tfsr() -#define arch_get_random_tag() mte_get_random_tag() +#define arch_set_random_tag(addr) mte_set_random_tag(addr) #define arch_get_mem_tag(addr) mte_get_mem_tag(addr) #define arch_set_mem_tag_range(addr, size, tag, init) \ mte_set_mem_tag_range((addr), (size), (tag), (init)) diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mt= e-kasan.h index b474fca3ea56..17e4155781fc 100644 --- a/arch/arm64/include/asm/mte-kasan.h +++ b/arch/arm64/include/asm/mte-kasan.h @@ -73,14 +73,14 @@ static inline u8 mte_get_mem_tag(void *addr) } =20 /* Generate a random tag. */ -static inline u8 mte_get_random_tag(void) +static inline void *mte_set_random_tag(const void *addr) { - void *addr; - + /* Writes the random MTE tag in bits [59:56]. */ asm volatile(__MTE_PREAMBLE "irg %0, %0" - : "=3Dr" (addr)); + : "+r" (addr)); =20 - return mte_get_ptr_tag(addr); + /* Sets bits [63:60] as KASAN expects. */ + return (void *)__tag_set(addr, mte_get_ptr_tag((void *)addr)); } =20 static inline u64 __stg_post(u64 p) @@ -190,9 +190,9 @@ static inline u8 mte_get_mem_tag(void *addr) return 0xFF; } =20 -static inline u8 mte_get_random_tag(void) +static inline void *mte_set_random_tag(const void *addr) { - return 0xFF; + return (void *)__tag_set(addr, 0xFF); } =20 static inline void mte_set_mem_tag_range(void *addr, size_t size, diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index be5dcf6b052c..0df7daee1864 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -433,7 +433,7 @@ static inline const void *arch_kasan_set_tag(const void= *addr, u8 tag) #define hw_suppress_tag_checks_stop() arch_suppress_tag_checks_stop() #define hw_flush_async_tag_fault() arch_flush_async_tag_fault() #define hw_enable_tag_checks_write_only() arch_enable_tag_checks_write_onl= y() -#define hw_get_random_tag() arch_get_random_tag() +#define hw_set_random_tag(addr) arch_set_random_tag(addr) #define hw_get_mem_tag(addr) arch_get_mem_tag(addr) #define hw_set_mem_tag_range(addr, size, tag, init) \ arch_set_mem_tag_range((addr), (size), (tag), (init)) @@ -469,7 +469,10 @@ static inline bool kasan_write_only_enabled(void) #ifdef CONFIG_KASAN_SW_TAGS u8 kasan_random_tag(void); #elif defined(CONFIG_KASAN_HW_TAGS) -static inline u8 kasan_random_tag(void) { return hw_get_random_tag(); } +static inline u8 kasan_random_tag(void) +{ + return get_tag(hw_set_random_tag(NULL)); +} #else static inline u8 kasan_random_tag(void) { return 0; } #endif --=20 2.56.0.455.g6c5a503b38-goog