diff options
| -rw-r--r-- | Documentation/dev-tools/kasan.rst | 17 | ||||
| -rw-r--r-- | include/linux/kasan.h | 14 | ||||
| -rw-r--r-- | mm/kasan/common.c | 9 | ||||
| -rw-r--r-- | mm/kasan/hw_tags.c | 60 | ||||
| -rw-r--r-- | mm/kasan/kasan.h | 27 | ||||
| -rw-r--r-- | mm/page_alloc.c | 43 |
6 files changed, 149 insertions, 21 deletions
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 5c93ab915049..e66916a483cd 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -140,6 +140,23 @@ 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 with the order equal or greater than + ``kasan.page_alloc.sample.order``, where N is the value of the ``sample`` + parameter (default: ``1``, or tag every such allocation). + This parameter is intended to mitigate the performance overhead introduced + by KASAN. + 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. + +- ``kasan.page_alloc.sample.order=<minimum page order>`` specifies the minimum + order of allocations that are affected by sampling (default: ``3``). + Only applies when ``kasan.page_alloc.sample`` is set to a value greater + than ``1``. + This parameter is intended to allow sampling only large page_alloc + allocations, which is the biggest source of the performance overhead. + Error reports ~~~~~~~~~~~~~ diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 96c9d56e5510..5ebbaf672009 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -120,12 +120,13 @@ 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, +bool __kasan_unpoison_pages(struct page *page, unsigned int order, bool init); +static __always_inline bool kasan_unpoison_pages(struct page *page, unsigned int order, bool init) { if (kasan_enabled()) - __kasan_unpoison_pages(page, order, init); + return __kasan_unpoison_pages(page, order, init); + return false; } void __kasan_cache_create_kmalloc(struct kmem_cache *cache); @@ -249,8 +250,11 @@ 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) +{ + 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/mm/kasan/common.c b/mm/kasan/common.c index 833bf2cfd2a3..1d0008e1c420 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c @@ -95,19 +95,24 @@ 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) { u8 tag; unsigned long i; if (unlikely(PageHighMem(page))) - return; + return false; + + if (!kasan_sample_page_alloc(order)) + 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..d1bcb0205327 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -59,6 +59,24 @@ EXPORT_SYMBOL_GPL(kasan_mode); /* Whether to enable vmalloc tagging. */ DEFINE_STATIC_KEY_TRUE(kasan_flag_vmalloc); +#define PAGE_ALLOC_SAMPLE_DEFAULT 1 +#define PAGE_ALLOC_SAMPLE_ORDER_DEFAULT 3 + +/* + * Sampling interval of page_alloc allocation (un)poisoning. + * Defaults to no sampling. + */ +unsigned long kasan_page_alloc_sample = PAGE_ALLOC_SAMPLE_DEFAULT; + +/* + * Minimum order of page_alloc allocations to be affected by sampling. + * The default value is chosen to match both + * PAGE_ALLOC_COSTLY_ORDER and SKB_FRAG_PAGE_ORDER. + */ +unsigned int kasan_page_alloc_sample_order = PAGE_ALLOC_SAMPLE_ORDER_DEFAULT; + +DEFINE_PER_CPU(long, kasan_page_alloc_skip); + /* kasan=off/on */ static int __init early_kasan_flag(char *arg) { @@ -122,6 +140,48 @@ 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 = PAGE_ALLOC_SAMPLE_DEFAULT; + return -EINVAL; + } + + return 0; +} +early_param("kasan.page_alloc.sample", early_kasan_flag_page_alloc_sample); + +/* kasan.page_alloc.sample.order=<minimum page order> */ +static int __init early_kasan_flag_page_alloc_sample_order(char *arg) +{ + int rv; + + if (!arg) + return -EINVAL; + + rv = kstrtouint(arg, 0, &kasan_page_alloc_sample_order); + if (rv) + return rv; + + if (kasan_page_alloc_sample_order > INT_MAX) { + kasan_page_alloc_sample_order = PAGE_ALLOC_SAMPLE_ORDER_DEFAULT; + return -EINVAL; + } + + return 0; +} +early_param("kasan.page_alloc.sample.order", early_kasan_flag_page_alloc_sample_order); + /* * 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 ea8cf1310b1e..32413f22aa82 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -42,6 +42,10 @@ enum kasan_mode { extern enum kasan_mode kasan_mode __ro_after_init; +extern unsigned long kasan_page_alloc_sample; +extern unsigned int kasan_page_alloc_sample_order; +DECLARE_PER_CPU(long, kasan_page_alloc_skip); + static inline bool kasan_vmalloc_enabled(void) { return static_branch_likely(&kasan_flag_vmalloc); @@ -57,6 +61,24 @@ 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(unsigned int order) +{ + /* Fast-path for when sampling is disabled. */ + if (kasan_page_alloc_sample == 1) + return true; + + if (order < kasan_page_alloc_sample_order) + return true; + + 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 +91,11 @@ static inline bool kasan_sync_fault_possible(void) return true; } +static inline bool kasan_sample_page_alloc(unsigned int order) +{ + return true; +} + #endif /* CONFIG_KASAN_HW_TAGS */ #ifdef CONFIG_KASAN_GENERIC diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 0745aedebb37..7d980dc0000e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1356,6 +1356,8 @@ out: * 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 @@ -2468,7 +2470,8 @@ 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); @@ -2491,30 +2494,42 @@ 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)) { + /* 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. */ |