From 0116523cfffa62aeb5aa3b85ce7419f3dae0c1b8 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Fri, 28 Dec 2018 00:29:37 -0800 Subject: kasan, mm: change hooks signatures Patch series "kasan: add software tag-based mode for arm64", v13. This patchset adds a new software tag-based mode to KASAN [1]. (Initially this mode was called KHWASAN, but it got renamed, see the naming rationale at the end of this section). The plan is to implement HWASan [2] for the kernel with the incentive, that it's going to have comparable to KASAN performance, but in the same time consume much less memory, trading that off for somewhat imprecise bug detection and being supported only for arm64. The underlying ideas of the approach used by software tag-based KASAN are: 1. By using the Top Byte Ignore (TBI) arm64 CPU feature, we can store pointer tags in the top byte of each kernel pointer. 2. Using shadow memory, we can store memory tags for each chunk of kernel memory. 3. On each memory allocation, we can generate a random tag, embed it into the returned pointer and set the memory tags that correspond to this chunk of memory to the same value. 4. By using compiler instrumentation, before each memory access we can add a check that the pointer tag matches the tag of the memory that is being accessed. 5. On a tag mismatch we report an error. With this patchset the existing KASAN mode gets renamed to generic KASAN, with the word "generic" meaning that the implementation can be supported by any architecture as it is purely software. The new mode this patchset adds is called software tag-based KASAN. The word "tag-based" refers to the fact that this mode uses tags embedded into the top byte of kernel pointers and the TBI arm64 CPU feature that allows to dereference such pointers. The word "software" here means that shadow memory manipulation and tag checking on pointer dereference is done in software. As it is the only tag-based implementation right now, "software tag-based" KASAN is sometimes referred to as simply "tag-based" in this patchset. A potential expansion of this mode is a hardware tag-based mode, which would use hardware memory tagging support (announced by Arm [3]) instead of compiler instrumentation and manual shadow memory manipulation. Same as generic KASAN, software tag-based KASAN is strictly a debugging feature. [1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html [2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html [3] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a ====== Rationale On mobile devices generic KASAN's memory usage is significant problem. One of the main reasons to have tag-based KASAN is to be able to perform a similar set of checks as the generic one does, but with lower memory requirements. Comment from Vishwath Mohan : I don't have data on-hand, but anecdotally both ASAN and KASAN have proven problematic to enable for environments that don't tolerate the increased memory pressure well. This includes (a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go, (c) Connected components like Pixel's visual core [1]. These are both places I'd love to have a low(er) memory footprint option at my disposal. Comment from Evgenii Stepanov : Looking at a live Android device under load, slab (according to /proc/meminfo) + kernel stack take 8-10% available RAM (~350MB). KASAN's overhead of 2x - 3x on top of it is not insignificant. Not having this overhead enables near-production use - ex. running KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do not reproduce in test configuration. These are the ones that often cost the most engineering time to track down. CPU overhead is bad, but generally tolerable. RAM is critical, in our experience. Once it gets low enough, OOM-killer makes your life miserable. [1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/ ====== Technical details Software tag-based KASAN mode is implemented in a very similar way to the generic one. This patchset essentially does the following: 1. TCR_TBI1 is set to enable Top Byte Ignore. 2. Shadow memory is used (with a different scale, 1:16, so each shadow byte corresponds to 16 bytes of kernel memory) to store memory tags. 3. All slab objects are aligned to shadow scale, which is 16 bytes. 4. All pointers returned from the slab allocator are tagged with a random tag and the corresponding shadow memory is poisoned with the same value. 5. Compiler instrumentation is used to insert tag checks. Either by calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE flags are reused). 6. When a tag mismatch is detected in callback instrumentation mode KASAN simply prints a bug report. In case of inline instrumentation, clang inserts a brk instruction, and KASAN has it's own brk handler, which reports the bug. 7. The memory in between slab objects is marked with a reserved tag, and acts as a redzone. 8. When a slab object is freed it's marked with a reserved tag. Bug detection is imprecise for two reasons: 1. We won't catch some small out-of-bounds accesses, that fall into the same shadow cell, as the last byte of a slab object. 2. We only have 1 byte to store tags, which means we have a 1/256 probability of a tag match for an incorrect access (actually even slightly less due to reserved tag values). Despite that there's a particular type of bugs that tag-based KASAN can detect compared to generic KASAN: use-after-free after the object has been allocated by someone else. ====== Testing Some kernel developers voiced a concern that changing the top byte of kernel pointers may lead to subtle bugs that are difficult to discover. To address this concern deliberate testing has been performed. It doesn't seem feasible to do some kind of static checking to find potential issues with pointer tagging, so a dynamic approach was taken. All pointer comparisons/subtractions have been instrumented in an LLVM compiler pass and a kernel module that would print a bug report whenever two pointers with different tags are being compared/subtracted (ignoring comparisons with NULL pointers and with pointers obtained by casting an error code to a pointer type) has been used. Then the kernel has been booted in QEMU and on an Odroid C2 board and syzkaller has been run. This yielded the following results. The two places that look interesting are: is_vmalloc_addr in include/linux/mm.h is_kernel_rodata in mm/util.c Here we compare a pointer with some fixed untagged values to make sure that the pointer lies in a particular part of the kernel address space. Since tag-based KASAN doesn't add tags to pointers that belong to rodata or vmalloc regions, this should work as is. To make sure debug checks to those two functions that check that the result doesn't change whether we operate on pointers with or without untagging has been added. A few other cases that don't look that interesting: Comparing pointers to achieve unique sorting order of pointee objects (e.g. sorting locks addresses before performing a double lock): tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c pipe_double_lock in fs/pipe.c unix_state_double_lock in net/unix/af_unix.c lock_two_nondirectories in fs/inode.c mutex_lock_double in kernel/events/core.c ep_cmp_ffd in fs/eventpoll.c fsnotify_compare_groups fs/notify/mark.c Nothing needs to be done here, since the tags embedded into pointers don't change, so the sorting order would still be unique. Checks that a pointer belongs to some particular allocation: is_sibling_entry in lib/radix-tree.c object_is_on_stack in include/linux/sched/task_stack.h Nothing needs to be done here either, since two pointers can only belong to the same allocation if they have the same tag. Overall, since the kernel boots and works, there are no critical bugs. As for the rest, the traditional kernel testing way (use until fails) is the only one that looks feasible. Another point here is that tag-based KASAN is available under a separate config option that needs to be deliberately enabled. Even though it might be used in a "near-production" environment to find bugs that are not found during fuzzing or running tests, it is still a debug tool. ====== Benchmarks The following numbers were collected on Odroid C2 board. Both generic and tag-based KASAN were used in inline instrumentation mode. Boot time [1]: * ~1.7 sec for clean kernel * ~5.0 sec for generic KASAN * ~5.0 sec for tag-based KASAN Network performance [2]: * 8.33 Gbits/sec for clean kernel * 3.17 Gbits/sec for generic KASAN * 2.85 Gbits/sec for tag-based KASAN Slab memory usage after boot [3]: * ~40 kb for clean kernel * ~105 kb (~260% overhead) for generic KASAN * ~47 kb (~20% overhead) for tag-based KASAN KASAN memory overhead consists of three main parts: 1. Increased slab memory usage due to redzones. 2. Shadow memory (the whole reserved once during boot). 3. Quaratine (grows gradually until some preset limit; the more the limit, the more the chance to detect a use-after-free). Comparing tag-based vs generic KASAN for each of these points: 1. 20% vs 260% overhead. 2. 1/16th vs 1/8th of physical memory. 3. Tag-based KASAN doesn't require quarantine. [1] Time before the ext4 driver is initialized. [2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`. [3] Measured as `cat /proc/meminfo | grep Slab`. ====== Some notes A few notes: 1. The patchset can be found here: https://github.com/xairy/kasan-prototype/tree/khwasan 2. Building requires a recent Clang version (7.0.0 or later). 3. Stack instrumentation is not supported yet and will be added later. This patch (of 25): Tag-based KASAN changes the value of the top byte of pointers returned from the kernel allocation functions (such as kmalloc). This patch updates KASAN hooks signatures and their usage in SLAB and SLUB code to reflect that. Link: http://lkml.kernel.org/r/aec2b5e3973781ff8a6bb6760f8543643202c451.1544099024.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Andrey Ryabinin Reviewed-by: Dmitry Vyukov Cc: Christoph Lameter Cc: Mark Rutland Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index e3629cd7aff1..fdd4a86aa882 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1372,10 +1372,10 @@ static inline void dec_slabs_node(struct kmem_cache *s, int node, * Hooks for other subsystems that check memory allocations. In a typical * production configuration these hooks all should produce no code at all. */ -static inline void kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags) +static inline void *kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags) { kmemleak_alloc(ptr, size, 1, flags); - kasan_kmalloc_large(ptr, size, flags); + return kasan_kmalloc_large(ptr, size, flags); } static __always_inline void kfree_hook(void *x) @@ -2768,7 +2768,7 @@ void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size) { void *ret = slab_alloc(s, gfpflags, _RET_IP_); trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags); - kasan_kmalloc(s, ret, size, gfpflags); + ret = kasan_kmalloc(s, ret, size, gfpflags); return ret; } EXPORT_SYMBOL(kmem_cache_alloc_trace); @@ -2796,7 +2796,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s, trace_kmalloc_node(_RET_IP_, ret, size, s->size, gfpflags, node); - kasan_kmalloc(s, ret, size, gfpflags); + ret = kasan_kmalloc(s, ret, size, gfpflags); return ret; } EXPORT_SYMBOL(kmem_cache_alloc_node_trace); @@ -3784,7 +3784,7 @@ void *__kmalloc(size_t size, gfp_t flags) trace_kmalloc(_RET_IP_, ret, size, s->size, flags); - kasan_kmalloc(s, ret, size, flags); + ret = kasan_kmalloc(s, ret, size, flags); return ret; } @@ -3801,8 +3801,7 @@ static void *kmalloc_large_node(size_t size, gfp_t flags, int node) if (page) ptr = page_address(page); - kmalloc_large_node_hook(ptr, size, flags); - return ptr; + return kmalloc_large_node_hook(ptr, size, flags); } void *__kmalloc_node(size_t size, gfp_t flags, int node) @@ -3829,7 +3828,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node) trace_kmalloc_node(_RET_IP_, ret, size, s->size, flags, node); - kasan_kmalloc(s, ret, size, flags); + ret = kasan_kmalloc(s, ret, size, flags); return ret; } -- cgit v1.2.3-58-ga151 From 12b22386998ccf97497a49c88f9579cf9c0dee55 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Fri, 28 Dec 2018 00:29:41 -0800 Subject: kasan, slub: handle pointer tags in early_kmem_cache_node_alloc The previous patch updated KASAN hooks signatures and their usage in SLAB and SLUB code, except for the early_kmem_cache_node_alloc function. This patch handles that function separately, as it requires to reorder some of the initialization code to correctly propagate a tagged pointer in case a tag is assigned by kasan_kmalloc. Link: http://lkml.kernel.org/r/fc8d0fdcf733a7a52e8d0daaa650f4736a57de8c.1544099024.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Cc: Andrey Ryabinin Cc: Christoph Lameter Cc: Dmitry Vyukov Cc: Mark Rutland Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index fdd4a86aa882..8561a32910dd 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3364,16 +3364,16 @@ static void early_kmem_cache_node_alloc(int node) n = page->freelist; BUG_ON(!n); - page->freelist = get_freepointer(kmem_cache_node, n); - page->inuse = 1; - page->frozen = 0; - kmem_cache_node->node[node] = n; #ifdef CONFIG_SLUB_DEBUG init_object(kmem_cache_node, n, SLUB_RED_ACTIVE); init_tracking(kmem_cache_node, n); #endif - kasan_kmalloc(kmem_cache_node, n, sizeof(struct kmem_cache_node), + n = kasan_kmalloc(kmem_cache_node, n, sizeof(struct kmem_cache_node), GFP_KERNEL); + page->freelist = get_freepointer(kmem_cache_node, n); + page->inuse = 1; + page->frozen = 0; + kmem_cache_node->node[node] = n; init_kmem_cache_node(n); inc_slabs_node(kmem_cache_node, node, page->objects); -- cgit v1.2.3-58-ga151 From 2bd926b439b4cb6b9ed240a9781cd01958b53d85 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Fri, 28 Dec 2018 00:29:53 -0800 Subject: kasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS This commit splits the current CONFIG_KASAN config option into two: 1. CONFIG_KASAN_GENERIC, that enables the generic KASAN mode (the one that exists now); 2. CONFIG_KASAN_SW_TAGS, that enables the software tag-based KASAN mode. The name CONFIG_KASAN_SW_TAGS is chosen as in the future we will have another hardware tag-based KASAN mode, that will rely on hardware memory tagging support in arm64. With CONFIG_KASAN_SW_TAGS enabled, compiler options are changed to instrument kernel files with -fsantize=kernel-hwaddress (except the ones for which KASAN_SANITIZE := n is set). Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_SW_TAGS support both CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes. This commit also adds empty placeholder (for now) implementation of tag-based KASAN specific hooks inserted by the compiler and adjusts common hooks implementation. While this commit adds the CONFIG_KASAN_SW_TAGS config option, this option is not selectable, as it depends on HAVE_ARCH_KASAN_SW_TAGS, which we will enable once all the infrastracture code has been added. Link: http://lkml.kernel.org/r/b2550106eb8a68b10fefbabce820910b115aa853.1544099024.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Andrey Ryabinin Reviewed-by: Dmitry Vyukov Cc: Christoph Lameter Cc: Mark Rutland Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/compiler-clang.h | 6 ++- include/linux/compiler-gcc.h | 6 +++ include/linux/compiler_attributes.h | 13 ----- include/linux/kasan.h | 16 ++++-- lib/Kconfig.kasan | 98 ++++++++++++++++++++++++++++--------- mm/kasan/Makefile | 6 ++- mm/kasan/generic.c | 2 +- mm/kasan/kasan.h | 3 +- mm/kasan/tags.c | 75 ++++++++++++++++++++++++++++ mm/slub.c | 2 +- scripts/Makefile.kasan | 53 +++++++++++--------- 11 files changed, 214 insertions(+), 66 deletions(-) create mode 100644 mm/kasan/tags.c (limited to 'mm/slub.c') diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index 3e7dafb3ea80..39f668d5066b 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -16,9 +16,13 @@ /* all clang versions usable with the kernel support KASAN ABI version 5 */ #define KASAN_ABI_VERSION 5 +#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer) /* emulate gcc's __SANITIZE_ADDRESS__ flag */ -#if __has_feature(address_sanitizer) #define __SANITIZE_ADDRESS__ +#define __no_sanitize_address \ + __attribute__((no_sanitize("address", "hwaddress"))) +#else +#define __no_sanitize_address #endif /* diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 2010493e1040..5776da43da97 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -143,6 +143,12 @@ #define KASAN_ABI_VERSION 3 #endif +#if __has_attribute(__no_sanitize_address__) +#define __no_sanitize_address __attribute__((no_sanitize_address)) +#else +#define __no_sanitize_address +#endif + #if GCC_VERSION >= 50100 #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 #endif diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index fe07b680dd4a..19f32b0c29af 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -199,19 +199,6 @@ */ #define __noreturn __attribute__((__noreturn__)) -/* - * Optional: only supported since gcc >= 4.8 - * Optional: not supported by icc - * - * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fsanitize_005faddress-function-attribute - * clang: https://clang.llvm.org/docs/AttributeReference.html#no-sanitize-address-no-address-safety-analysis - */ -#if __has_attribute(__no_sanitize_address__) -# define __no_sanitize_address __attribute__((__no_sanitize_address__)) -#else -# define __no_sanitize_address -#endif - /* * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 52c86a568a4e..b66fdf5ea7ab 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -45,8 +45,6 @@ void kasan_free_pages(struct page *page, unsigned int order); void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, slab_flags_t *flags); -void kasan_cache_shrink(struct kmem_cache *cache); -void kasan_cache_shutdown(struct kmem_cache *cache); void kasan_poison_slab(struct page *page); void kasan_unpoison_object_data(struct kmem_cache *cache, void *object); @@ -97,8 +95,6 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {} static inline void kasan_cache_create(struct kmem_cache *cache, unsigned int *size, slab_flags_t *flags) {} -static inline void kasan_cache_shrink(struct kmem_cache *cache) {} -static inline void kasan_cache_shutdown(struct kmem_cache *cache) {} static inline void kasan_poison_slab(struct page *page) {} static inline void kasan_unpoison_object_data(struct kmem_cache *cache, @@ -155,4 +151,16 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; } #endif /* CONFIG_KASAN */ +#ifdef CONFIG_KASAN_GENERIC + +void kasan_cache_shrink(struct kmem_cache *cache); +void kasan_cache_shutdown(struct kmem_cache *cache); + +#else /* CONFIG_KASAN_GENERIC */ + +static inline void kasan_cache_shrink(struct kmem_cache *cache) {} +static inline void kasan_cache_shutdown(struct kmem_cache *cache) {} + +#endif /* CONFIG_KASAN_GENERIC */ + #endif /* LINUX_KASAN_H */ diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan index d0bad1bd9a2b..d8c474b6691e 100644 --- a/lib/Kconfig.kasan +++ b/lib/Kconfig.kasan @@ -1,36 +1,92 @@ +# This config refers to the generic KASAN mode. config HAVE_ARCH_KASAN bool -if HAVE_ARCH_KASAN +config HAVE_ARCH_KASAN_SW_TAGS + bool + +config CC_HAS_KASAN_GENERIC + def_bool $(cc-option, -fsanitize=kernel-address) + +config CC_HAS_KASAN_SW_TAGS + def_bool $(cc-option, -fsanitize=kernel-hwaddress) config KASAN - bool "KASan: runtime memory debugger" + bool "KASAN: runtime memory debugger" + depends on (HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC) || \ + (HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS) + depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB) + help + Enables KASAN (KernelAddressSANitizer) - runtime memory debugger, + designed to find out-of-bounds accesses and use-after-free bugs. + See Documentation/dev-tools/kasan.rst for details. + +choice + prompt "KASAN mode" + depends on KASAN + default KASAN_GENERIC + help + KASAN has two modes: generic KASAN (similar to userspace ASan, + x86_64/arm64/xtensa, enabled with CONFIG_KASAN_GENERIC) and + software tag-based KASAN (a version based on software memory + tagging, arm64 only, similar to userspace HWASan, enabled with + CONFIG_KASAN_SW_TAGS). + Both generic and tag-based KASAN are strictly debugging features. + +config KASAN_GENERIC + bool "Generic mode" + depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB) select SLUB_DEBUG if SLUB select CONSTRUCTORS select STACKDEPOT help - Enables kernel address sanitizer - runtime memory debugger, - designed to find out-of-bounds accesses and use-after-free bugs. - This is strictly a debugging feature and it requires a gcc version - of 4.9.2 or later. Detection of out of bounds accesses to stack or - global variables requires gcc 5.0 or later. - This feature consumes about 1/8 of available memory and brings about - ~x3 performance slowdown. + Enables generic KASAN mode. + Supported in both GCC and Clang. With GCC it requires version 4.9.2 + or later for basic support and version 5.0 or later for detection of + out-of-bounds accesses for stack and global variables and for inline + instrumentation mode (CONFIG_KASAN_INLINE). With Clang it requires + version 3.7.0 or later and it doesn't support detection of + out-of-bounds accesses for global variables yet. + This mode consumes about 1/8th of available memory at kernel start + and introduces an overhead of ~x1.5 for the rest of the allocations. + The performance slowdown is ~x3. For better error detection enable CONFIG_STACKTRACE. - Currently CONFIG_KASAN doesn't work with CONFIG_DEBUG_SLAB + Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB (the resulting kernel does not boot). +config KASAN_SW_TAGS + bool "Software tag-based mode" + depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS + depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB) + select SLUB_DEBUG if SLUB + select CONSTRUCTORS + select STACKDEPOT + help + Enables software tag-based KASAN mode. + This mode requires Top Byte Ignore support by the CPU and therefore + is only supported for arm64. + This mode requires Clang version 7.0.0 or later. + This mode consumes about 1/16th of available memory at kernel start + and introduces an overhead of ~20% for the rest of the allocations. + This mode may potentially introduce problems relating to pointer + casting and comparison, as it embeds tags into the top byte of each + pointer. + For better error detection enable CONFIG_STACKTRACE. + Currently CONFIG_KASAN_SW_TAGS doesn't work with CONFIG_DEBUG_SLAB + (the resulting kernel does not boot). + +endchoice + config KASAN_EXTRA - bool "KAsan: extra checks" - depends on KASAN && DEBUG_KERNEL && !COMPILE_TEST + bool "KASAN: extra checks" + depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST help - This enables further checks in the kernel address sanitizer, for now - it only includes the address-use-after-scope check that can lead - to excessive kernel stack usage, frame size warnings and longer + This enables further checks in generic KASAN, for now it only + includes the address-use-after-scope check that can lead to + excessive kernel stack usage, frame size warnings and longer compile time. - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 has more - + See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 choice prompt "Instrumentation type" @@ -53,7 +109,7 @@ config KASAN_INLINE memory accesses. This is faster than outline (in some workloads it gives about x2 boost over outline instrumentation), but make kernel's .text size much bigger. - This requires a gcc version of 5.0 or later. + For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later. endchoice @@ -67,11 +123,9 @@ config KASAN_S390_4_LEVEL_PAGING 4-level paging instead. config TEST_KASAN - tristate "Module for testing kasan for bug detection" + tristate "Module for testing KASAN for bug detection" depends on m && KASAN help This is a test module doing various nasty things like out of bounds accesses, use after free. It is useful for testing - kernel debugging features like kernel address sanitizer. - -endif + kernel debugging features like KASAN. diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile index d643530b24aa..68ba1822f003 100644 --- a/mm/kasan/Makefile +++ b/mm/kasan/Makefile @@ -2,6 +2,7 @@ KASAN_SANITIZE := n UBSAN_SANITIZE_common.o := n UBSAN_SANITIZE_generic.o := n +UBSAN_SANITIZE_tags.o := n KCOV_INSTRUMENT := n CFLAGS_REMOVE_generic.o = -pg @@ -10,5 +11,8 @@ CFLAGS_REMOVE_generic.o = -pg CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) CFLAGS_generic.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) +CFLAGS_tags.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) -obj-y := common.o generic.o report.o init.o quarantine.o +obj-$(CONFIG_KASAN) := common.o init.o report.o +obj-$(CONFIG_KASAN_GENERIC) += generic.o quarantine.o +obj-$(CONFIG_KASAN_SW_TAGS) += tags.o diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c index 44ec228de0a2..b8de6d33c55c 100644 --- a/mm/kasan/generic.c +++ b/mm/kasan/generic.c @@ -1,5 +1,5 @@ /* - * This file contains core KASAN code. + * This file contains core generic KASAN code. * * Copyright (c) 2014 Samsung Electronics Co., Ltd. * Author: Andrey Ryabinin diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index 659463800f10..19b950eaccff 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -114,7 +114,8 @@ void kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip); void kasan_report_invalid_free(void *object, unsigned long ip); -#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB) +#if defined(CONFIG_KASAN_GENERIC) && \ + (defined(CONFIG_SLAB) || defined(CONFIG_SLUB)) void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache); void quarantine_reduce(void); void quarantine_remove_cache(struct kmem_cache *cache); diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c new file mode 100644 index 000000000000..04194923c543 --- /dev/null +++ b/mm/kasan/tags.c @@ -0,0 +1,75 @@ +/* + * This file contains core tag-based KASAN code. + * + * Copyright (c) 2018 Google, Inc. + * Author: Andrey Konovalov + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt +#define DISABLE_BRANCH_PROFILING + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "kasan.h" +#include "../slab.h" + +void check_memory_region(unsigned long addr, size_t size, bool write, + unsigned long ret_ip) +{ +} + +#define DEFINE_HWASAN_LOAD_STORE(size) \ + void __hwasan_load##size##_noabort(unsigned long addr) \ + { \ + } \ + EXPORT_SYMBOL(__hwasan_load##size##_noabort); \ + void __hwasan_store##size##_noabort(unsigned long addr) \ + { \ + } \ + EXPORT_SYMBOL(__hwasan_store##size##_noabort) + +DEFINE_HWASAN_LOAD_STORE(1); +DEFINE_HWASAN_LOAD_STORE(2); +DEFINE_HWASAN_LOAD_STORE(4); +DEFINE_HWASAN_LOAD_STORE(8); +DEFINE_HWASAN_LOAD_STORE(16); + +void __hwasan_loadN_noabort(unsigned long addr, unsigned long size) +{ +} +EXPORT_SYMBOL(__hwasan_loadN_noabort); + +void __hwasan_storeN_noabort(unsigned long addr, unsigned long size) +{ +} +EXPORT_SYMBOL(__hwasan_storeN_noabort); + +void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size) +{ +} +EXPORT_SYMBOL(__hwasan_tag_memory); diff --git a/mm/slub.c b/mm/slub.c index 8561a32910dd..e739d46600b9 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2992,7 +2992,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page, do_slab_free(s, page, head, tail, cnt, addr); } -#ifdef CONFIG_KASAN +#ifdef CONFIG_KASAN_GENERIC void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr) { do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr); diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan index 69552a39951d..25c259df8ffa 100644 --- a/scripts/Makefile.kasan +++ b/scripts/Makefile.kasan @@ -1,5 +1,6 @@ # SPDX-License-Identifier: GPL-2.0 -ifdef CONFIG_KASAN +ifdef CONFIG_KASAN_GENERIC + ifdef CONFIG_KASAN_INLINE call_threshold := 10000 else @@ -12,36 +13,44 @@ CFLAGS_KASAN_MINIMAL := -fsanitize=kernel-address cc-param = $(call cc-option, -mllvm -$(1), $(call cc-option, --param $(1))) -ifeq ($(call cc-option, $(CFLAGS_KASAN_MINIMAL) -Werror),) - ifneq ($(CONFIG_COMPILE_TEST),y) - $(warning Cannot use CONFIG_KASAN: \ - -fsanitize=kernel-address is not supported by compiler) - endif -else - # -fasan-shadow-offset fails without -fsanitize - CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \ +# -fasan-shadow-offset fails without -fsanitize +CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \ -fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \ $(call cc-option, -fsanitize=kernel-address \ -mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET))) - ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),) - CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL) - else - # Now add all the compiler specific options that are valid standalone - CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \ - $(call cc-param,asan-globals=1) \ - $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \ - $(call cc-param,asan-stack=1) \ - $(call cc-param,asan-use-after-scope=1) \ - $(call cc-param,asan-instrument-allocas=1) - endif - +ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),) + CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL) +else + # Now add all the compiler specific options that are valid standalone + CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \ + $(call cc-param,asan-globals=1) \ + $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \ + $(call cc-param,asan-stack=1) \ + $(call cc-param,asan-use-after-scope=1) \ + $(call cc-param,asan-instrument-allocas=1) endif ifdef CONFIG_KASAN_EXTRA CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope) endif -CFLAGS_KASAN_NOSANITIZE := -fno-builtin +endif # CONFIG_KASAN_GENERIC +ifdef CONFIG_KASAN_SW_TAGS + +ifdef CONFIG_KASAN_INLINE + instrumentation_flags := -mllvm -hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET) +else + instrumentation_flags := -mllvm -hwasan-instrument-with-calls=1 +endif + +CFLAGS_KASAN := -fsanitize=kernel-hwaddress \ + -mllvm -hwasan-instrument-stack=0 \ + $(instrumentation_flags) + +endif # CONFIG_KASAN_SW_TAGS + +ifdef CONFIG_KASAN +CFLAGS_KASAN_NOSANITIZE := -fno-builtin endif -- cgit v1.2.3-58-ga151 From 4d176711ea7a8d4873e7157ac6ab242ade3ba351 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Fri, 28 Dec 2018 00:30:23 -0800 Subject: kasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU An object constructor can initialize pointers within this objects based on the address of the object. Since the object address might be tagged, we need to assign a tag before calling constructor. The implemented approach is to assign tags to objects with constructors when a slab is allocated and call constructors once as usual. The downside is that such object would always have the same tag when it is reallocated, so we won't catch use-after-frees on it. Also pressign tags for objects from SLAB_TYPESAFE_BY_RCU caches, since they can be validy accessed after having been freed. Link: http://lkml.kernel.org/r/f158a8a74a031d66f0a9398a5b0ed453c37ba09a.1544099024.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Andrey Ryabinin Reviewed-by: Dmitry Vyukov Cc: Christoph Lameter Cc: Mark Rutland Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slab.c | 2 +- mm/slub.c | 24 ++++++++++++++---------- 2 files changed, 15 insertions(+), 11 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slab.c b/mm/slab.c index 0f0cfd6cd48a..15e53cef0378 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -2574,7 +2574,7 @@ static void cache_init_objs(struct kmem_cache *cachep, for (i = 0; i < cachep->num; i++) { objp = index_to_obj(cachep, page, i); - kasan_init_slab_obj(cachep, objp); + objp = kasan_init_slab_obj(cachep, objp); /* constructor could break poison info */ if (DEBUG == 0 && cachep->ctor) { diff --git a/mm/slub.c b/mm/slub.c index e739d46600b9..08740c3f3745 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1451,16 +1451,17 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s, #endif } -static void setup_object(struct kmem_cache *s, struct page *page, +static void *setup_object(struct kmem_cache *s, struct page *page, void *object) { setup_object_debug(s, page, object); - kasan_init_slab_obj(s, object); + object = kasan_init_slab_obj(s, object); if (unlikely(s->ctor)) { kasan_unpoison_object_data(s, object); s->ctor(object); kasan_poison_object_data(s, object); } + return object; } /* @@ -1568,16 +1569,16 @@ static bool shuffle_freelist(struct kmem_cache *s, struct page *page) /* First entry is used as the base of the freelist */ cur = next_freelist_entry(s, page, &pos, start, page_limit, freelist_count); + cur = setup_object(s, page, cur); page->freelist = cur; for (idx = 1; idx < page->objects; idx++) { - setup_object(s, page, cur); next = next_freelist_entry(s, page, &pos, start, page_limit, freelist_count); + next = setup_object(s, page, next); set_freepointer(s, cur, next); cur = next; } - setup_object(s, page, cur); set_freepointer(s, cur, NULL); return true; @@ -1599,7 +1600,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) struct page *page; struct kmem_cache_order_objects oo = s->oo; gfp_t alloc_gfp; - void *start, *p; + void *start, *p, *next; int idx, order; bool shuffle; @@ -1651,13 +1652,16 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) if (!shuffle) { for_each_object_idx(p, idx, s, start, page->objects) { - setup_object(s, page, p); - if (likely(idx < page->objects)) - set_freepointer(s, p, p + s->size); - else + if (likely(idx < page->objects)) { + next = p + s->size; + next = setup_object(s, page, next); + set_freepointer(s, p, next); + } else set_freepointer(s, p, NULL); } - page->freelist = fixup_red_left(s, start); + start = fixup_red_left(s, start); + start = setup_object(s, page, start); + page->freelist = start; } page->inuse = page->objects; -- cgit v1.2.3-58-ga151 From 1265ef2de4cef44cec91ba47009958eec6162836 Mon Sep 17 00:00:00 2001 From: Wei Yang Date: Fri, 28 Dec 2018 00:33:06 -0800 Subject: mm/slub.c: remove validation on cpu_slab in __flush_cpu_slab() cpu_slab is a per cpu variable which is allocated in all or none. If a cpu_slab failed to be allocated, the slub is not usable. We could use cpu_slab without validation in __flush_cpu_slab(). Link: http://lkml.kernel.org/r/20181103141218.22844-1-richard.weiyang@gmail.com Signed-off-by: Wei Yang Reviewed-by: Andrew Morton Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index 08740c3f3745..3fd791c0dae5 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2317,12 +2317,10 @@ static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu) { struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu); - if (likely(c)) { - if (c->page) - flush_slab(s, c); + if (c->page) + flush_slab(s, c); - unfreeze_partials(s, c); - } + unfreeze_partials(s, c); } static void flush_cpu_slab(void *d) -- cgit v1.2.3-58-ga151 From 6159d0f5c03e81daed29657e60383ee27f979b4a Mon Sep 17 00:00:00 2001 From: Wei Yang Date: Fri, 28 Dec 2018 00:33:09 -0800 Subject: mm/slub.c: page is always non-NULL in node_match() node_match() is a static function and is only invoked in slub.c. In all three places, `page' is ensured to be valid. Link: http://lkml.kernel.org/r/20181106150245.1668-1-richard.weiyang@gmail.com Signed-off-by: Wei Yang Acked-by: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index 3fd791c0dae5..011e53e5845b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2369,7 +2369,7 @@ static int slub_cpu_dead(unsigned int cpu) static inline int node_match(struct page *page, int node) { #ifdef CONFIG_NUMA - if (!page || (node != NUMA_NO_NODE && page_to_nid(page) != node)) + if (node != NUMA_NO_NODE && page_to_nid(page) != node) return 0; #endif return 1; -- cgit v1.2.3-58-ga151 From 88349a2837fbaef83862a011e1f53c4551d3e199 Mon Sep 17 00:00:00 2001 From: Wei Yang Date: Fri, 28 Dec 2018 00:33:13 -0800 Subject: mm/slub.c: record final state of slub action in deactivate_slab() If __cmpxchg_double_slab() fails and (l != m), current code records transition states of slub action. Update the action after __cmpxchg_double_slab() success to record the final state. [akpm@linux-foundation.org: more whitespace cleanup] Link: http://lkml.kernel.org/r/20181107013119.3816-1-richard.weiyang@gmail.com Signed-off-by: Wei Yang Reviewed-by: Andrew Morton Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 21 +++++++-------------- 1 file changed, 7 insertions(+), 14 deletions(-) (limited to 'mm/slub.c') diff --git a/mm/slub.c b/mm/slub.c index 011e53e5845b..36c0befeebd8 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2131,26 +2131,15 @@ redo: } if (l != m) { - if (l == M_PARTIAL) - remove_partial(n, page); - else if (l == M_FULL) - remove_full(s, n, page); - if (m == M_PARTIAL) { - + if (m == M_PARTIAL) add_partial(n, page, tail); - stat(s, tail); - - } else if (m == M_FULL) { - - stat(s, DEACTIVATE_FULL); + else if (m == M_FULL) add_full(s, n, page); - - } } l = m; @@ -2163,7 +2152,11 @@ redo: if (lock) spin_unlock(&n->list_lock); - if (m == M_FREE) { + if (m == M_PARTIAL) + stat(s, tail); + else if (m == M_FULL) + stat(s, DEACTIVATE_FULL); + else if (m == M_FREE) { stat(s, DEACTIVATE_EMPTY); discard_slab(s, page); stat(s, FREE_SLAB); -- cgit v1.2.3-58-ga151