From e60beb95c08baf29416d0e06a9e1d4887faf5d1c Mon Sep 17 00:00:00 2001 From: Vincenzo Frascino Date: Mon, 15 Mar 2021 13:20:15 +0000 Subject: [PATCH] arm64: mte: Enable TCO in functions that can read beyond buffer limits load_unaligned_zeropad() and __get/put_kernel_nofault() functions can read past some buffer limits which may include some MTE granule with a different tag. When MTE async mode is enabled, the load operation crosses the boundaries and the next granule has a different tag the PE sets the TFSR_EL1.TF1 bit as if an asynchronous tag fault is happened. Enable Tag Check Override (TCO) in these functions before the load and disable it afterwards to prevent this to happen. Note: The same condition can be hit in MTE sync mode but we deal with it through the exception handling. In the current implementation, mte_async_mode flag is set only at boot time but in future kasan might acquire some runtime features that that change the mode dynamically, hence we disable it when sync mode is selected for future proof. Cc: Will Deacon Reported-by: Branislav Rankov Tested-by: Branislav Rankov Reviewed-by: Catalin Marinas Acked-by: Andrey Konovalov Tested-by: Andrey Konovalov Signed-off-by: Vincenzo Frascino Link: https://lore.kernel.org/r/20210315132019.33202-6-vincenzo.frascino@arm.com Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/mte.h | 15 +++++++++++++++ arch/arm64/include/asm/uaccess.h | 22 ++++++++++++++++++++++ arch/arm64/include/asm/word-at-a-time.h | 4 ++++ arch/arm64/kernel/mte.c | 22 ++++++++++++++++++++++ 4 files changed, 63 insertions(+) diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index 9b557a4..8603c66 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -90,5 +90,20 @@ static inline void mte_assign_mem_tag_range(void *addr, size_t size) #endif /* CONFIG_ARM64_MTE */ +#ifdef CONFIG_KASAN_HW_TAGS +/* Whether the MTE asynchronous mode is enabled. */ +DECLARE_STATIC_KEY_FALSE(mte_async_mode); + +static inline bool system_uses_mte_async_mode(void) +{ + return static_branch_unlikely(&mte_async_mode); +} +#else +static inline bool system_uses_mte_async_mode(void) +{ + return false; +} +#endif /* CONFIG_KASAN_HW_TAGS */ + #endif /* __ASSEMBLY__ */ #endif /* __ASM_MTE_H */ diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index 0deb884..b5f0862 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -20,6 +20,7 @@ #include #include +#include #include #include #include @@ -188,6 +189,23 @@ static inline void __uaccess_enable_tco(void) ARM64_MTE, CONFIG_KASAN_HW_TAGS)); } +/* + * These functions disable tag checking only if in MTE async mode + * since the sync mode generates exceptions synchronously and the + * nofault or load_unaligned_zeropad can handle them. + */ +static inline void __uaccess_disable_tco_async(void) +{ + if (system_uses_mte_async_mode()) + __uaccess_disable_tco(); +} + +static inline void __uaccess_enable_tco_async(void) +{ + if (system_uses_mte_async_mode()) + __uaccess_enable_tco(); +} + static inline void uaccess_disable_privileged(void) { __uaccess_disable_tco(); @@ -307,8 +325,10 @@ do { \ do { \ int __gkn_err = 0; \ \ + __uaccess_enable_tco_async(); \ __raw_get_mem("ldr", *((type *)(dst)), \ (__force type *)(src), __gkn_err); \ + __uaccess_disable_tco_async(); \ if (unlikely(__gkn_err)) \ goto err_label; \ } while (0) @@ -380,8 +400,10 @@ do { \ do { \ int __pkn_err = 0; \ \ + __uaccess_enable_tco_async(); \ __raw_put_mem("str", *((type *)(src)), \ (__force type *)(dst), __pkn_err); \ + __uaccess_disable_tco_async(); \ if (unlikely(__pkn_err)) \ goto err_label; \ } while(0) diff --git a/arch/arm64/include/asm/word-at-a-time.h b/arch/arm64/include/asm/word-at-a-time.h index 3333950..c62d9fa 100644 --- a/arch/arm64/include/asm/word-at-a-time.h +++ b/arch/arm64/include/asm/word-at-a-time.h @@ -55,6 +55,8 @@ static inline unsigned long load_unaligned_zeropad(const void *addr) { unsigned long ret, offset; + __uaccess_enable_tco_async(); + /* Load word from unaligned pointer addr */ asm( "1: ldr %0, %3\n" @@ -76,6 +78,8 @@ static inline unsigned long load_unaligned_zeropad(const void *addr) : "=&r" (ret), "=&r" (offset) : "r" (addr), "Q" (*(unsigned long *)addr)); + __uaccess_disable_tco_async(); + return ret; } diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index fa755cf..9362928 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -26,6 +26,10 @@ u64 gcr_kernel_excl __ro_after_init; static bool report_fault_once = true; +/* Whether the MTE asynchronous mode is enabled. */ +DEFINE_STATIC_KEY_FALSE(mte_async_mode); +EXPORT_SYMBOL_GPL(mte_async_mode); + static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) { pte_t old_pte = READ_ONCE(*ptep); @@ -118,12 +122,30 @@ static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) 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(), + "MTE async mode enabled system wide!"); + __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC); } void mte_enable_kernel_async(void) { __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); + + /* + * MTE async 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_mode()) + static_branch_enable(&mte_async_mode); } void mte_set_report_once(bool state) -- 2.7.4