kmsan_init() is a macro that takes a possibly uninitialized value and returns an initialized value of the same type. It can be used e.g. in cases when a value comes from non-instrumented code to avoid false positive reports. In particular, we use kmsan_init() in READ_ONCE_NOCHECK() so that it returns initialized values. This helps defeat false positives e.g. from leftover stack contents accessed by stack unwinders. Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> --- Link: https://linux-review.googlesource.com/id/Icd1260073666f944922f031bfb6762379ba1fa38 --- include/asm-generic/rwonce.h | 5 +++-- include/linux/kmsan-checks.h | 40 ++++++++++++++++++++++++++++++++++++ mm/kmsan/Makefile | 5 ++++- mm/kmsan/annotations.c | 28 +++++++++++++++++++++++++ 4 files changed, 75 insertions(+), 3 deletions(-) create mode 100644 mm/kmsan/annotations.c diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h index 8d0a6280e9824..7cf993af8e1ea 100644 --- a/include/asm-generic/rwonce.h +++ b/include/asm-generic/rwonce.h @@ -25,6 +25,7 @@ #include <linux/compiler_types.h> #include <linux/kasan-checks.h> #include <linux/kcsan-checks.h> +#include <linux/kmsan-checks.h> /* * Yes, this permits 64-bit accesses on 32-bit architectures. These will @@ -69,14 +70,14 @@ unsigned long __read_once_word_nocheck(const void *addr) /* * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a - * word from memory atomically but without telling KASAN/KCSAN. This is + * word from memory atomically but without telling KASAN/KCSAN/KMSAN. This is * usually used by unwinding code when walking the stack of a running process. */ #define READ_ONCE_NOCHECK(x) \ ({ \ compiletime_assert(sizeof(x) == sizeof(unsigned long), \ "Unsupported access size for READ_ONCE_NOCHECK()."); \ - (typeof(x))__read_once_word_nocheck(&(x)); \ + kmsan_init((typeof(x))__read_once_word_nocheck(&(x))); \ }) static __no_kasan_or_inline diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h index a6522a0c28df9..ecd8336190fc0 100644 --- a/include/linux/kmsan-checks.h +++ b/include/linux/kmsan-checks.h @@ -14,6 +14,44 @@ #ifdef CONFIG_KMSAN +/* + * Helper functions that mark the return value initialized. + * See mm/kmsan/annotations.c. + */ +u8 kmsan_init_1(u8 value); +u16 kmsan_init_2(u16 value); +u32 kmsan_init_4(u32 value); +u64 kmsan_init_8(u64 value); + +static inline void *kmsan_init_ptr(void *ptr) +{ + return (void *)kmsan_init_8((u64)ptr); +} + +static inline char kmsan_init_char(char value) +{ + return (u8)kmsan_init_1((u8)value); +} + +#define __decl_kmsan_init_type(type, fn) unsigned type : fn, signed type : fn + +/** + * kmsan_init - Make the value initialized. + * @val: 1-, 2-, 4- or 8-byte integer that may be treated as uninitialized by + * KMSAN. + * + * Return: value of @val that KMSAN treats as initialized. + */ +#define kmsan_init(val) \ + ( \ + (typeof(val))(_Generic((val), \ + __decl_kmsan_init_type(char, kmsan_init_1), \ + __decl_kmsan_init_type(short, kmsan_init_2), \ + __decl_kmsan_init_type(int, kmsan_init_4), \ + __decl_kmsan_init_type(long, kmsan_init_8), \ + char : kmsan_init_char, \ + void * : kmsan_init_ptr)(val))) + /** * kmsan_poison_memory() - Mark the memory range as uninitialized. * @address: address to start with. @@ -48,6 +86,8 @@ void kmsan_check_memory(const void *address, size_t size); #else +#define kmsan_init(value) (value) + static inline void kmsan_poison_memory(const void *address, size_t size, gfp_t flags) { diff --git a/mm/kmsan/Makefile b/mm/kmsan/Makefile index a80dde1de7048..73b705cbf75b9 100644 --- a/mm/kmsan/Makefile +++ b/mm/kmsan/Makefile @@ -1,9 +1,11 @@ -obj-y := core.o instrumentation.o hooks.o report.o shadow.o +obj-y := core.o instrumentation.o hooks.o report.o shadow.o annotations.o KMSAN_SANITIZE := n KCOV_INSTRUMENT := n UBSAN_SANITIZE := n +KMSAN_SANITIZE_kmsan_annotations.o := y + # Disable instrumentation of KMSAN runtime with other tools. CC_FLAGS_KMSAN_RUNTIME := -fno-stack-protector CC_FLAGS_KMSAN_RUNTIME += $(call cc-option,-fno-conserve-stack) @@ -11,6 +13,7 @@ CC_FLAGS_KMSAN_RUNTIME += -DDISABLE_BRANCH_PROFILING CFLAGS_REMOVE.o = $(CC_FLAGS_FTRACE) +CFLAGS_annotations.o := $(CC_FLAGS_KMSAN_RUNTIME) CFLAGS_core.o := $(CC_FLAGS_KMSAN_RUNTIME) CFLAGS_hooks.o := $(CC_FLAGS_KMSAN_RUNTIME) CFLAGS_instrumentation.o := $(CC_FLAGS_KMSAN_RUNTIME) diff --git a/mm/kmsan/annotations.c b/mm/kmsan/annotations.c new file mode 100644 index 0000000000000..8ccde90bcd12b --- /dev/null +++ b/mm/kmsan/annotations.c @@ -0,0 +1,28 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * KMSAN annotations. + * + * The kmsan_init_SIZE functions reside in a separate translation unit to + * prevent inlining them. Clang may inline functions marked with + * __no_sanitize_memory attribute into functions without it, which effectively + * results in ignoring the attribute. + * + * Copyright (C) 2017-2022 Google LLC + * Author: Alexander Potapenko <glider@xxxxxxxxxx> + * + */ + +#include <linux/export.h> +#include <linux/kmsan-checks.h> + +#define DECLARE_KMSAN_INIT(size, t) \ + __no_sanitize_memory t kmsan_init_##size(t value) \ + { \ + return value; \ + } \ + EXPORT_SYMBOL(kmsan_init_##size) + +DECLARE_KMSAN_INIT(1, u8); +DECLARE_KMSAN_INIT(2, u16); +DECLARE_KMSAN_INIT(4, u32); +DECLARE_KMSAN_INIT(8, u64); -- 2.36.0.rc2.479.g8af0fa9b8e-goog
