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Message-Id: <4c341c5609ed09ad6d52f937eeec28d142ff1f46.1669489329.git.andreyknvl@google.com> Date: Sat, 26 Nov 2022 20:12:12 +0100 From: andrey.konovalov@...ux.dev To: Marco Elver <elver@...gle.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com> Cc: Andrey Konovalov <andreyknvl@...il.com>, Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Andrey Ryabinin <ryabinin.a.a@...il.com>, kasan-dev@...glegroups.com, Peter Collingbourne <pcc@...gle.com>, Evgenii Stepanov <eugenis@...gle.com>, Florian Mayer <fmayer@...gle.com>, Jann Horn <jannh@...gle.com>, Mark Brand <markbrand@...gle.com>, netdev@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrey Konovalov <andreyknvl@...gle.com> Subject: [PATCH v2 1/2] kasan: allow sampling page_alloc allocations for HW_TAGS From: Andrey Konovalov <andreyknvl@...gle.com> Add a new boot parameter called kasan.page_alloc.sample, which makes Hardware Tag-Based KASAN tag only every Nth page_alloc allocation for allocations marked with __GFP_KASAN_SAMPLE. As Hardware Tag-Based KASAN is intended to be used in production, its performance impact is crucial. As page_alloc allocations tend to be big, tagging and checking all such allocations can introduce a significant slowdown. The new flag allows to alleviate that slowdown for chosen allocations. The exact performance improvement caused by using __GFP_KASAN_SAMPLE and kasan.page_alloc.sample depends on how often the marked allocations happen and how large the are. See the next patch for the details about marking and sampling skb allocations. Enabling page_alloc sampling has a downside: KASAN will miss bad accesses to a page_alloc allocation that has not been tagged. Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com> --- Changes v1->v2: - Only sample allocations when __GFP_KASAN_SAMPLE is provided to alloc_pages(). - Fix build when KASAN is disabled. - Add more information about the flag to documentation. - Use optimized preemption-safe approach for sampling suggested by Marco. --- Documentation/dev-tools/kasan.rst | 8 ++++++ include/linux/gfp_types.h | 10 +++++-- include/linux/kasan.h | 18 ++++++++----- include/trace/events/mmflags.h | 3 ++- mm/kasan/common.c | 10 +++++-- mm/kasan/hw_tags.c | 26 ++++++++++++++++++ mm/kasan/kasan.h | 19 +++++++++++++ mm/mempool.c | 2 +- mm/page_alloc.c | 44 +++++++++++++++++++++---------- 9 files changed, 114 insertions(+), 26 deletions(-) diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 5c93ab915049..bd6d064c7419 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -140,6 +140,14 @@ disabling KASAN altogether or controlling its features: - ``kasan.vmalloc=off`` or ``=on`` disables or enables tagging of vmalloc allocations (default: ``on``). +- ``kasan.page_alloc.sample=<sampling interval>`` makes KASAN tag only every + Nth page_alloc allocation for allocations marked with __GFP_KASAN_SAMPLE, + where N is the value of the parameter (default: ``1``). + This parameter is intended to mitigate the performance overhead. + Note that enabling this parameter makes Hardware Tag-Based KASAN skip checks + of allocations chosen by sampling and thus miss bad accesses to these + allocations. Use the default value for accurate bug detection. + Error reports ~~~~~~~~~~~~~ diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h index d88c46ca82e1..c322cd159445 100644 --- a/include/linux/gfp_types.h +++ b/include/linux/gfp_types.h @@ -50,13 +50,15 @@ typedef unsigned int __bitwise gfp_t; #define ___GFP_SKIP_ZERO 0x1000000u #define ___GFP_SKIP_KASAN_UNPOISON 0x2000000u #define ___GFP_SKIP_KASAN_POISON 0x4000000u +#define ___GFP_KASAN_SAMPLE 0x8000000u #else #define ___GFP_SKIP_ZERO 0 #define ___GFP_SKIP_KASAN_UNPOISON 0 #define ___GFP_SKIP_KASAN_POISON 0 +#define ___GFP_KASAN_SAMPLE 0 #endif #ifdef CONFIG_LOCKDEP -#define ___GFP_NOLOCKDEP 0x8000000u +#define ___GFP_NOLOCKDEP 0x10000000u #else #define ___GFP_NOLOCKDEP 0 #endif @@ -243,6 +245,9 @@ typedef unsigned int __bitwise gfp_t; * * %__GFP_SKIP_KASAN_POISON makes KASAN skip poisoning on page deallocation. * Typically, used for userspace pages. Only effective in HW_TAGS mode. + * + * %__GFP_KASAN_SAMPLE makes KASAN use sampling to skip poisoning and + * unpoisoning of page allocations. Only effective in HW_TAGS mode. */ #define __GFP_NOWARN ((__force gfp_t)___GFP_NOWARN) #define __GFP_COMP ((__force gfp_t)___GFP_COMP) @@ -251,12 +256,13 @@ typedef unsigned int __bitwise gfp_t; #define __GFP_SKIP_ZERO ((__force gfp_t)___GFP_SKIP_ZERO) #define __GFP_SKIP_KASAN_UNPOISON ((__force gfp_t)___GFP_SKIP_KASAN_UNPOISON) #define __GFP_SKIP_KASAN_POISON ((__force gfp_t)___GFP_SKIP_KASAN_POISON) +#define __GFP_KASAN_SAMPLE ((__force gfp_t)___GFP_KASAN_SAMPLE) /* Disable lockdep for GFP context tracking */ #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP) /* Room for N __GFP_FOO bits */ -#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP)) +#define __GFP_BITS_SHIFT (28 + IS_ENABLED(CONFIG_LOCKDEP)) #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1)) /** diff --git a/include/linux/kasan.h b/include/linux/kasan.h index d811b3d7d2a1..4cc946b8cbc8 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -120,12 +120,15 @@ static __always_inline void kasan_poison_pages(struct page *page, __kasan_poison_pages(page, order, init); } -void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init); -static __always_inline void kasan_unpoison_pages(struct page *page, - unsigned int order, bool init) +bool __kasan_unpoison_pages(struct page *page, unsigned int order, + bool init, bool sample); +static __always_inline bool kasan_unpoison_pages(struct page *page, + unsigned int order, + bool init, bool sample) { if (kasan_enabled()) - __kasan_unpoison_pages(page, order, init); + return __kasan_unpoison_pages(page, order, init, sample); + return false; } void __kasan_cache_create_kmalloc(struct kmem_cache *cache); @@ -249,8 +252,11 @@ static __always_inline bool kasan_check_byte(const void *addr) static inline void kasan_unpoison_range(const void *address, size_t size) {} static inline void kasan_poison_pages(struct page *page, unsigned int order, bool init) {} -static inline void kasan_unpoison_pages(struct page *page, unsigned int order, - bool init) {} +static inline bool kasan_unpoison_pages(struct page *page, unsigned int order, + bool init, bool sample) +{ + return false; +} static inline void kasan_cache_create_kmalloc(struct kmem_cache *cache) {} static inline void kasan_poison_slab(struct slab *slab) {} static inline void kasan_unpoison_object_data(struct kmem_cache *cache, diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h index e87cb2b80ed3..bcaecf859d1f 100644 --- a/include/trace/events/mmflags.h +++ b/include/trace/events/mmflags.h @@ -57,7 +57,8 @@ #define __def_gfpflag_names_kasan , \ gfpflag_string(__GFP_SKIP_ZERO), \ gfpflag_string(__GFP_SKIP_KASAN_POISON), \ - gfpflag_string(__GFP_SKIP_KASAN_UNPOISON) + gfpflag_string(__GFP_SKIP_KASAN_UNPOISON), \ + gfpflag_string(__GFP_KASAN_SAMPLE) #else #define __def_gfpflag_names_kasan #endif diff --git a/mm/kasan/common.c b/mm/kasan/common.c index 833bf2cfd2a3..05d799ada873 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c @@ -95,19 +95,25 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark) } #endif /* CONFIG_KASAN_STACK */ -void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init) +bool __kasan_unpoison_pages(struct page *page, unsigned int order, + bool init, bool sample) { u8 tag; unsigned long i; if (unlikely(PageHighMem(page))) - return; + return false; + + if (sample && !kasan_sample_page_alloc()) + return false; tag = kasan_random_tag(); kasan_unpoison(set_tag(page_address(page), tag), PAGE_SIZE << order, init); for (i = 0; i < (1 << order); i++) page_kasan_tag_set(page + i, tag); + + return true; } void __kasan_poison_pages(struct page *page, unsigned int order, bool init) diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c index b22c4f461cb0..5e6571820a3f 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -59,6 +59,11 @@ EXPORT_SYMBOL_GPL(kasan_mode); /* Whether to enable vmalloc tagging. */ DEFINE_STATIC_KEY_TRUE(kasan_flag_vmalloc); +/* Sampling interval of page_alloc allocation (un)poisoning. */ +unsigned long kasan_page_alloc_sample = 1; + +DEFINE_PER_CPU(long, kasan_page_alloc_skip); + /* kasan=off/on */ static int __init early_kasan_flag(char *arg) { @@ -122,6 +127,27 @@ static inline const char *kasan_mode_info(void) return "sync"; } +/* kasan.page_alloc.sample=<sampling interval> */ +static int __init early_kasan_flag_page_alloc_sample(char *arg) +{ + int rv; + + if (!arg) + return -EINVAL; + + rv = kstrtoul(arg, 0, &kasan_page_alloc_sample); + if (rv) + return rv; + + if (!kasan_page_alloc_sample || kasan_page_alloc_sample > LONG_MAX) { + kasan_page_alloc_sample = 1; + return -EINVAL; + } + + return 0; +} +early_param("kasan.page_alloc.sample", early_kasan_flag_page_alloc_sample); + /* * kasan_init_hw_tags_cpu() is called for each CPU. * Not marked as __init as a CPU can be hot-plugged after boot. diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index abbcc1b0eec5..ce0b30889587 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -42,6 +42,9 @@ enum kasan_mode { extern enum kasan_mode kasan_mode __ro_after_init; +extern unsigned long kasan_page_alloc_sample; +DECLARE_PER_CPU(long, kasan_page_alloc_skip); + static inline bool kasan_vmalloc_enabled(void) { return static_branch_likely(&kasan_flag_vmalloc); @@ -57,6 +60,17 @@ static inline bool kasan_sync_fault_possible(void) return kasan_mode == KASAN_MODE_SYNC || kasan_mode == KASAN_MODE_ASYMM; } +static inline bool kasan_sample_page_alloc(void) +{ + if (this_cpu_dec_return(kasan_page_alloc_skip) < 0) { + this_cpu_write(kasan_page_alloc_skip, + kasan_page_alloc_sample - 1); + return true; + } + + return false; +} + #else /* CONFIG_KASAN_HW_TAGS */ static inline bool kasan_async_fault_possible(void) @@ -69,6 +83,11 @@ static inline bool kasan_sync_fault_possible(void) return true; } +static inline bool kasan_sample_page_alloc(void) +{ + return true; +} + #endif /* CONFIG_KASAN_HW_TAGS */ #ifdef CONFIG_KASAN_GENERIC diff --git a/mm/mempool.c b/mm/mempool.c index 96488b13a1ef..d3b3702e5191 100644 --- a/mm/mempool.c +++ b/mm/mempool.c @@ -115,7 +115,7 @@ static void kasan_unpoison_element(mempool_t *pool, void *element) kasan_unpoison_range(element, __ksize(element)); else if (pool->alloc == mempool_alloc_pages) kasan_unpoison_pages(element, (unsigned long)pool->pool_data, - false); + false, false); } static __always_inline void add_element(mempool_t *pool, void *element) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6e60657875d3..969b0e4f0046 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1367,6 +1367,8 @@ static int free_tail_pages_check(struct page *head_page, struct page *page) * see the comment next to it. * 3. Skipping poisoning is requested via __GFP_SKIP_KASAN_POISON, * see the comment next to it. + * 4. The allocation is excluded from being checked due to sampling, + * see the call to kasan_unpoison_pages. * * Poisoning pages during deferred memory init will greatly lengthen the * process and cause problem in large memory systems as the deferred pages @@ -2476,7 +2478,8 @@ inline void post_alloc_hook(struct page *page, unsigned int order, { bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags) && !should_skip_init(gfp_flags); - bool init_tags = init && (gfp_flags & __GFP_ZEROTAGS); + bool zero_tags = init && (gfp_flags & __GFP_ZEROTAGS); + bool reset_tags = !zero_tags; int i; set_page_private(page, 0); @@ -2499,30 +2502,43 @@ inline void post_alloc_hook(struct page *page, unsigned int order, */ /* - * If memory tags should be zeroed (which happens only when memory - * should be initialized as well). + * If memory tags should be zeroed + * (which happens only when memory should be initialized as well). */ - if (init_tags) { + if (zero_tags) { /* Initialize both memory and tags. */ for (i = 0; i != 1 << order; ++i) tag_clear_highpage(page + i); - /* Note that memory is already initialized by the loop above. */ + /* Take note that memory was initialized by the loop above. */ init = false; } if (!should_skip_kasan_unpoison(gfp_flags)) { - /* Unpoison shadow memory or set memory tags. */ - kasan_unpoison_pages(page, order, init); - - /* Note that memory is already initialized by KASAN. */ - if (kasan_has_integrated_init()) - init = false; - } else { - /* Ensure page_address() dereferencing does not fault. */ + /* Try unpoisoning (or setting tags) and initializing memory. */ + if (kasan_unpoison_pages(page, order, init, + gfp_flags & __GFP_KASAN_SAMPLE)) { + /* Take note that memory was initialized by KASAN. */ + if (kasan_has_integrated_init()) + init = false; + /* Take note that memory tags were set by KASAN. */ + reset_tags = false; + } else { + /* + * KASAN decided to exclude this allocation from being + * poisoned due to sampling. Skip poisoning as well. + */ + SetPageSkipKASanPoison(page); + } + } + /* + * If memory tags have not been set, reset the page tags to ensure + * page_address() dereferencing does not fault. + */ + if (reset_tags) { for (i = 0; i != 1 << order; ++i) page_kasan_tag_reset(page + i); } - /* If memory is still not initialized, do it now. */ + /* If memory is still not initialized, initialize it now. */ if (init) kernel_init_pages(page, 1 << order); /* Propagate __GFP_SKIP_KASAN_POISON to page flags. */ -- 2.25.1
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