From 8028caaca7a8107a52bb28fd92dea35bebd7ae8e Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Tue, 22 Dec 2020 12:03:06 -0800 Subject: [PATCH] kasan: add and integrate kasan boot parameters Hardware tag-based KASAN mode is intended to eventually be used in production as a security mitigation. Therefore there's a need for finer control over KASAN features and for an existence of a kill switch. This change adds a few boot parameters for hardware tag-based KASAN that allow to disable or otherwise control particular KASAN features. The features that can be controlled are: 1. Whether KASAN is enabled at all. 2. Whether KASAN collects and saves alloc/free stacks. 3. Whether KASAN panics on a detected bug or not. With this change a new boot parameter kasan.mode allows to choose one of three main modes: - kasan.mode=off - KASAN is disabled, no tag checks are performed - kasan.mode=prod - only essential production features are enabled - kasan.mode=full - all KASAN features are enabled The chosen mode provides default control values for the features mentioned above. However it's also possible to override the default values by providing: - kasan.stacktrace=off/on - enable alloc/free stack collection (default: on for mode=full, otherwise off) - kasan.fault=report/panic - only report tag fault or also panic (default: report) If kasan.mode parameter is not provided, it defaults to full when CONFIG_DEBUG_KERNEL is enabled, and to prod otherwise. It is essential that switching between these modes doesn't require rebuilding the kernel with different configs, as this is required by the Android GKI (Generic Kernel Image) initiative [1]. [1] https://source.android.com/devices/architecture/kernel/generic-kernel-image [andreyknvl@google.com: don't use read-only static keys] Link: https://lkml.kernel.org/r/f2ded589eba1597f7360a972226083de9afd86e2.1607537948.git.andreyknvl@google.com Link: https://lkml.kernel.org/r/cb093613879d8d8841173f090133eddeb4c35f1f.1606162397.git.andreyknvl@google.com Link: https://linux-review.googlesource.com/id/If7d37003875b2ed3e0935702c8015c223d6416a4 Signed-off-by: Andrey Konovalov Reviewed-by: Marco Elver Reviewed-by: Dmitry Vyukov Tested-by: Vincenzo Frascino Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Branislav Rankov Cc: Catalin Marinas Cc: Evgenii Stepanov Cc: Kevin Brodsky Cc: Vasily Gorbik Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/kasan/common.c | 22 +++++-- mm/kasan/hw_tags.c | 151 +++++++++++++++++++++++++++++++++++++++++++++ mm/kasan/kasan.h | 16 +++++ mm/kasan/report.c | 14 ++++- 4 files changed, 196 insertions(+), 7 deletions(-) diff --git a/mm/kasan/common.c b/mm/kasan/common.c index 780ec27459ab..219c2979bd3e 100644 --- a/mm/kasan/common.c +++ b/mm/kasan/common.c @@ -134,6 +134,11 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, unsigned int redzone_size; int redzone_adjust; + if (!kasan_stack_collection_enabled()) { + *flags |= SLAB_KASAN; + return; + } + /* Add alloc meta. */ cache->kasan_info.alloc_meta_offset = *size; *size += sizeof(struct kasan_alloc_meta); @@ -170,6 +175,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, size_t kasan_metadata_size(struct kmem_cache *cache) { + if (!kasan_stack_collection_enabled()) + return 0; return (cache->kasan_info.alloc_meta_offset ? sizeof(struct kasan_alloc_meta) : 0) + (cache->kasan_info.free_meta_offset ? @@ -262,11 +269,13 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache, { struct kasan_alloc_meta *alloc_meta; - if (!(cache->flags & SLAB_KASAN)) - return (void *)object; + if (kasan_stack_collection_enabled()) { + if (!(cache->flags & SLAB_KASAN)) + return (void *)object; - alloc_meta = kasan_get_alloc_meta(cache, object); - __memset(alloc_meta, 0, sizeof(*alloc_meta)); + alloc_meta = kasan_get_alloc_meta(cache, object); + __memset(alloc_meta, 0, sizeof(*alloc_meta)); + } if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS)) object = set_tag(object, assign_tag(cache, object, true, false)); @@ -303,6 +312,9 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object, rounded_up_size = round_up(cache->object_size, KASAN_GRANULE_SIZE); poison_range(object, rounded_up_size, KASAN_KMALLOC_FREE); + if (!kasan_stack_collection_enabled()) + return false; + if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) || unlikely(!(cache->flags & SLAB_KASAN))) return false; @@ -350,7 +362,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object, poison_range((void *)redzone_start, redzone_end - redzone_start, KASAN_KMALLOC_REDZONE); - if (cache->flags & SLAB_KASAN) + if (kasan_stack_collection_enabled() && (cache->flags & SLAB_KASAN)) set_alloc_info(cache, (void *)object, flags); return set_tag(object, tag); diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c index 863fed4edd3f..4ccc3c873c82 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -8,18 +8,115 @@ #define pr_fmt(fmt) "kasan: " fmt +#include #include #include #include #include +#include #include #include #include "kasan.h" +enum kasan_arg_mode { + KASAN_ARG_MODE_DEFAULT, + KASAN_ARG_MODE_OFF, + KASAN_ARG_MODE_PROD, + KASAN_ARG_MODE_FULL, +}; + +enum kasan_arg_stacktrace { + KASAN_ARG_STACKTRACE_DEFAULT, + KASAN_ARG_STACKTRACE_OFF, + KASAN_ARG_STACKTRACE_ON, +}; + +enum kasan_arg_fault { + KASAN_ARG_FAULT_DEFAULT, + KASAN_ARG_FAULT_REPORT, + KASAN_ARG_FAULT_PANIC, +}; + +static enum kasan_arg_mode kasan_arg_mode __ro_after_init; +static enum kasan_arg_stacktrace kasan_arg_stacktrace __ro_after_init; +static enum kasan_arg_fault kasan_arg_fault __ro_after_init; + +/* Whether KASAN is enabled at all. */ +DEFINE_STATIC_KEY_FALSE(kasan_flag_enabled); +EXPORT_SYMBOL(kasan_flag_enabled); + +/* Whether to collect alloc/free stack traces. */ +DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace); + +/* Whether panic or disable tag checking on fault. */ +bool kasan_flag_panic __ro_after_init; + +/* kasan.mode=off/prod/full */ +static int __init early_kasan_mode(char *arg) +{ + if (!arg) + return -EINVAL; + + if (!strcmp(arg, "off")) + kasan_arg_mode = KASAN_ARG_MODE_OFF; + else if (!strcmp(arg, "prod")) + kasan_arg_mode = KASAN_ARG_MODE_PROD; + else if (!strcmp(arg, "full")) + kasan_arg_mode = KASAN_ARG_MODE_FULL; + else + return -EINVAL; + + return 0; +} +early_param("kasan.mode", early_kasan_mode); + +/* kasan.stack=off/on */ +static int __init early_kasan_flag_stacktrace(char *arg) +{ + if (!arg) + return -EINVAL; + + if (!strcmp(arg, "off")) + kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_OFF; + else if (!strcmp(arg, "on")) + kasan_arg_stacktrace = KASAN_ARG_STACKTRACE_ON; + else + return -EINVAL; + + return 0; +} +early_param("kasan.stacktrace", early_kasan_flag_stacktrace); + +/* kasan.fault=report/panic */ +static int __init early_kasan_fault(char *arg) +{ + if (!arg) + return -EINVAL; + + if (!strcmp(arg, "report")) + kasan_arg_fault = KASAN_ARG_FAULT_REPORT; + else if (!strcmp(arg, "panic")) + kasan_arg_fault = KASAN_ARG_FAULT_PANIC; + else + return -EINVAL; + + return 0; +} +early_param("kasan.fault", early_kasan_fault); + /* kasan_init_hw_tags_cpu() is called for each CPU. */ void kasan_init_hw_tags_cpu(void) { + /* + * There's no need to check that the hardware is MTE-capable here, + * as this function is only called for MTE-capable hardware. + */ + + /* If KASAN is disabled, do nothing. */ + if (kasan_arg_mode == KASAN_ARG_MODE_OFF) + return; + hw_init_tags(KASAN_TAG_MAX); hw_enable_tagging(); } @@ -27,6 +124,60 @@ void kasan_init_hw_tags_cpu(void) /* kasan_init_hw_tags() is called once on boot CPU. */ void __init kasan_init_hw_tags(void) { + /* If hardware doesn't support MTE, do nothing. */ + if (!system_supports_mte()) + return; + + /* Choose KASAN mode if kasan boot parameter is not provided. */ + if (kasan_arg_mode == KASAN_ARG_MODE_DEFAULT) { + if (IS_ENABLED(CONFIG_DEBUG_KERNEL)) + kasan_arg_mode = KASAN_ARG_MODE_FULL; + else + kasan_arg_mode = KASAN_ARG_MODE_PROD; + } + + /* Preset parameter values based on the mode. */ + switch (kasan_arg_mode) { + case KASAN_ARG_MODE_DEFAULT: + /* Shouldn't happen as per the check above. */ + WARN_ON(1); + return; + case KASAN_ARG_MODE_OFF: + /* If KASAN is disabled, do nothing. */ + return; + case KASAN_ARG_MODE_PROD: + static_branch_enable(&kasan_flag_enabled); + break; + case KASAN_ARG_MODE_FULL: + static_branch_enable(&kasan_flag_enabled); + static_branch_enable(&kasan_flag_stacktrace); + break; + } + + /* Now, optionally override the presets. */ + + switch (kasan_arg_stacktrace) { + case KASAN_ARG_STACKTRACE_DEFAULT: + break; + case KASAN_ARG_STACKTRACE_OFF: + static_branch_disable(&kasan_flag_stacktrace); + break; + case KASAN_ARG_STACKTRACE_ON: + static_branch_enable(&kasan_flag_stacktrace); + break; + } + + switch (kasan_arg_fault) { + case KASAN_ARG_FAULT_DEFAULT: + break; + case KASAN_ARG_FAULT_REPORT: + kasan_flag_panic = false; + break; + case KASAN_ARG_FAULT_PANIC: + kasan_flag_panic = true; + break; + } + pr_info("KernelAddressSanitizer initialized\n"); } diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index 6e811d0f6242..ca43de9811de 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -5,6 +5,22 @@ #include #include +#ifdef CONFIG_KASAN_HW_TAGS +#include +DECLARE_STATIC_KEY_FALSE(kasan_flag_stacktrace); +static inline bool kasan_stack_collection_enabled(void) +{ + return static_branch_unlikely(&kasan_flag_stacktrace); +} +#else +static inline bool kasan_stack_collection_enabled(void) +{ + return true; +} +#endif + +extern bool kasan_flag_panic __ro_after_init; + #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) #define KASAN_GRANULE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT) #else diff --git a/mm/kasan/report.c b/mm/kasan/report.c index 00c590efdaea..ed9555a814df 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -99,6 +99,10 @@ static void end_report(unsigned long *flags) panic_on_warn = 0; panic("panic_on_warn set ...\n"); } +#ifdef CONFIG_KASAN_HW_TAGS + if (kasan_flag_panic) + panic("kasan.fault=panic set ...\n"); +#endif kasan_enable_current(); } @@ -161,8 +165,8 @@ static void describe_object_addr(struct kmem_cache *cache, void *object, (void *)(object_addr + cache->object_size)); } -static void describe_object(struct kmem_cache *cache, void *object, - const void *addr, u8 tag) +static void describe_object_stacks(struct kmem_cache *cache, void *object, + const void *addr, u8 tag) { struct kasan_alloc_meta *alloc_meta = kasan_get_alloc_meta(cache, object); @@ -190,7 +194,13 @@ static void describe_object(struct kmem_cache *cache, void *object, } #endif } +} +static void describe_object(struct kmem_cache *cache, void *object, + const void *addr, u8 tag) +{ + if (kasan_stack_collection_enabled()) + describe_object_stacks(cache, object, addr, tag); describe_object_addr(cache, object, addr); }