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Biederman" , Ingo Molnar , Paul Lawrence , Geert Uytterhoeven , Arnd Bergmann , "Kirill A . Shutemov" , Greg Kroah-Hartman , Kate Stewart , Mike Rapoport , kasan-dev@googlegroups.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sparse@vger.kernel.org, linux-mm@kvack.org, linux-kbuild@vger.kernel.org Cc: Kostya Serebryany , Evgeniy Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Jann Horn , Mark Brand , Chintan Pandya , Vishwath Mohan , Andrey Konovalov Subject: [PATCH v11 10/24] kasan: add tag related helper functions Date: Mon, 19 Nov 2018 18:26:26 +0100 Message-Id: X-Mailer: git-send-email 2.19.1.1215.g8438c0b245-goog In-Reply-To: References: MIME-Version: 1.0 Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This commit adds a few helper functions, that are meant to be used to work with tags embedded in the top byte of kernel pointers: to set, to get or to reset the top byte. Signed-off-by: Andrey Konovalov --- arch/arm64/include/asm/kasan.h | 8 +++++-- arch/arm64/include/asm/memory.h | 12 +++++++++++ arch/arm64/mm/kasan_init.c | 2 ++ include/linux/kasan.h | 13 ++++++++++++ mm/kasan/kasan.h | 31 +++++++++++++++++++++++++++ mm/kasan/tags.c | 37 +++++++++++++++++++++++++++++++++ 6 files changed, 101 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h index 8758bb008436..b52aacd2c526 100644 --- a/arch/arm64/include/asm/kasan.h +++ b/arch/arm64/include/asm/kasan.h @@ -4,12 +4,16 @@ #ifndef __ASSEMBLY__ -#ifdef CONFIG_KASAN - #include #include #include +#define arch_kasan_set_tag(addr, tag) __tag_set(addr, tag) +#define arch_kasan_reset_tag(addr) __tag_reset(addr) +#define arch_kasan_get_tag(addr) __tag_get(addr) + +#ifdef CONFIG_KASAN + /* * KASAN_SHADOW_START: beginning of the kernel virtual addresses. * KASAN_SHADOW_END: KASAN_SHADOW_START + 1/N of kernel virtual addresses, diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index deb95be44392..ae741827039c 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -94,6 +94,18 @@ #define KASAN_THREAD_SHIFT 0 #endif +#ifdef CONFIG_KASAN_SW_TAGS +#define __tag_shifted(tag) ((__u64)(tag) << 56) +#define __tag_set(addr, tag) (__typeof__(addr))( \ + ((__u64)(addr) & ~__tag_shifted(0xff)) | __tag_shifted(tag)) +#define __tag_reset(addr) untagged_addr(addr) +#define __tag_get(addr) (__u8)((__u64)(addr) >> 56) +#else +#define __tag_set(addr, tag) (addr) +#define __tag_reset(addr) (addr) +#define __tag_get(addr) 0 +#endif + #define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT) /* diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c index 7a4a0904cac8..1df536bdabcb 100644 --- a/arch/arm64/mm/kasan_init.c +++ b/arch/arm64/mm/kasan_init.c @@ -253,6 +253,8 @@ void __init kasan_init(void) memset(kasan_early_shadow_page, KASAN_SHADOW_INIT, PAGE_SIZE); cpu_replace_ttbr1(lm_alias(swapper_pg_dir)); + kasan_init_tags(); + /* At this point kasan is fully initialized. Enable error messages */ init_task.kasan_depth = 0; pr_info("KernelAddressSanitizer initialized\n"); diff --git a/include/linux/kasan.h b/include/linux/kasan.h index c56af24bd3e7..a477ce2abdc9 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -169,6 +169,19 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {} #define KASAN_SHADOW_INIT 0xFF +void kasan_init_tags(void); + +void *kasan_reset_tag(const void *addr); + +#else /* CONFIG_KASAN_SW_TAGS */ + +static inline void kasan_init_tags(void) { } + +static inline void *kasan_reset_tag(const void *addr) +{ + return (void *)addr; +} + #endif /* CONFIG_KASAN_SW_TAGS */ #endif /* LINUX_KASAN_H */ diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index 19b950eaccff..6e42f46522c0 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -8,6 +8,10 @@ #define KASAN_SHADOW_SCALE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT) #define KASAN_SHADOW_MASK (KASAN_SHADOW_SCALE_SIZE - 1) +#define KASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */ +#define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */ +#define KASAN_TAG_MAX 0xFD /* maximum value for random tags */ + #define KASAN_FREE_PAGE 0xFF /* page was freed */ #define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */ #define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */ @@ -126,6 +130,33 @@ static inline void quarantine_reduce(void) { } static inline void quarantine_remove_cache(struct kmem_cache *cache) { } #endif +#ifdef CONFIG_KASAN_SW_TAGS + +u8 random_tag(void); + +#else + +static inline u8 random_tag(void) +{ + return 0; +} + +#endif + +#ifndef arch_kasan_set_tag +#define arch_kasan_set_tag(addr, tag) (void *)addr +#endif +#ifndef arch_kasan_reset_tag +#define arch_kasan_reset_tag(addr) (void *)addr +#endif +#ifndef arch_kasan_get_tag +#define arch_kasan_get_tag(addr) 0 +#endif + +#define set_tag(addr, tag) (void *)arch_kasan_set_tag(addr, tag) +#define reset_tag(addr) (void *)arch_kasan_reset_tag(addr) +#define get_tag(addr) arch_kasan_get_tag(addr) + /* * Exported functions for interfaces called from assembly or from generated * code. Declarations here to avoid warning about missing declarations. diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c index 04194923c543..1c4e7ce2e6fe 100644 --- a/mm/kasan/tags.c +++ b/mm/kasan/tags.c @@ -38,6 +38,43 @@ #include "kasan.h" #include "../slab.h" +static DEFINE_PER_CPU(u32, prng_state); + +void kasan_init_tags(void) +{ + int cpu; + + for_each_possible_cpu(cpu) + per_cpu(prng_state, cpu) = get_random_u32(); +} + +/* + * If a preemption happens between this_cpu_read and this_cpu_write, the only + * side effect is that we'll give a few allocated in different contexts objects + * the same tag. Since tag-based KASAN is meant to be used a probabilistic + * bug-detection debug feature, this doesn't have significant negative impact. + * + * Ideally the tags use strong randomness to prevent any attempts to predict + * them during explicit exploit attempts. But strong randomness is expensive, + * and we did an intentional trade-off to use a PRNG. This non-atomic RMW + * sequence has in fact positive effect, since interrupts that randomly skew + * PRNG at unpredictable points do only good. + */ +u8 random_tag(void) +{ + u32 state = this_cpu_read(prng_state); + + state = 1664525 * state + 1013904223; + this_cpu_write(prng_state, state); + + return (u8)(state % (KASAN_TAG_MAX + 1)); +} + +void *kasan_reset_tag(const void *addr) +{ + return reset_tag(addr); +} + void check_memory_region(unsigned long addr, size_t size, bool write, unsigned long ret_ip) {