On Mon, Nov 16, 2020 at 4:15 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > On Fri, Nov 13, 2020 at 11:20PM +0100, Andrey Konovalov wrote: > > 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 > > > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > > Link: https://linux-review.googlesource.com/id/If7d37003875b2ed3e0935702c8015c223d6416a4 > > Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Much nicer with the wrappers now. Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > > --- > > 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 1ac4f435c679..a11e3e75eb08 100644 > > --- a/mm/kasan/common.c > > +++ b/mm/kasan/common.c > > @@ -135,6 +135,11 @@ 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); > > @@ -171,6 +176,8 @@ 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 ? > > @@ -263,11 +270,13 @@ 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)); > > @@ -307,6 +316,9 @@ 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; > > @@ -357,7 +369,7 @@ 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..30ce88935e9d 100644 > > --- a/mm/kasan/hw_tags.c > > +++ b/mm/kasan/hw_tags.c > > @@ -8,18 +8,115 @@ > > > > #define pr_fmt(fmt) "kasan: " fmt > > > > +#include <linux/init.h> > > #include <linux/kasan.h> > > #include <linux/kernel.h> > > #include <linux/memory.h> > > #include <linux/mm.h> > > +#include <linux/static_key.h> > > #include <linux/string.h> > > #include <linux/types.h> > > > > #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_RO(kasan_flag_enabled); > > +EXPORT_SYMBOL(kasan_flag_enabled); > > + > > +/* Whether to collect alloc/free stack traces. */ > > +DEFINE_STATIC_KEY_FALSE_RO(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 8aa83b7ad79e..d01a5ac34f70 100644 > > --- a/mm/kasan/kasan.h > > +++ b/mm/kasan/kasan.h > > @@ -6,6 +6,22 @@ > > #include <linux/kfence.h> > > #include <linux/stackdepot.h> > > > > +#ifdef CONFIG_KASAN_HW_TAGS > > +#include <linux/static_key.h> > > +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 76a0e3ae2049..ffa6076b1710 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); > > } > > > > -- > > 2.29.2.299.gdc1121823c-goog > >
