From 439a1bcac648fe9b59210cde8991fb2acf37bdab Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 19 Sep 2022 15:53:13 -0700 Subject: [PATCH] fortify: Use __builtin_dynamic_object_size() when available Since the commits starting with c37495d6254c ("slab: add __alloc_size attributes for better bounds checking"), the compilers have runtime allocation size hints available in some places. This was immediately available to CONFIG_UBSAN_BOUNDS, but CONFIG_FORTIFY_SOURCE needed updating to explicitly make use of the hints via the associated __builtin_dynamic_object_size() helper. Detect and use the builtin when it is available, increasing the accuracy of the mitigation. When runtime sizes are not available, __builtin_dynamic_object_size() falls back to __builtin_object_size(), leaving the existing bounds checking unchanged. Additionally update the VMALLOC_LINEAR_OVERFLOW LKDTM test to make the hint invisible, otherwise the architectural defense is not exercised (the buffer overflow is detected in the memset() rather than when it crosses the edge of the allocation). Cc: Arnd Bergmann Cc: Greg Kroah-Hartman Cc: Nick Desaulniers Cc: Nathan Chancellor Cc: Tom Rix Cc: linux-hardening@vger.kernel.org Cc: llvm@lists.linux.dev Reviewed-by: Miguel Ojeda # include/linux/compiler_attributes.h Signed-off-by: Kees Cook --- drivers/misc/lkdtm/heap.c | 1 + include/linux/compiler_attributes.h | 5 +++++ include/linux/fortify-string.h | 7 +++++++ 3 files changed, 13 insertions(+) diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c index 62516078a619..0ce4cbf6abda 100644 --- a/drivers/misc/lkdtm/heap.c +++ b/drivers/misc/lkdtm/heap.c @@ -31,6 +31,7 @@ static void lkdtm_VMALLOC_LINEAR_OVERFLOW(void) char *one, *two; one = vzalloc(PAGE_SIZE); + OPTIMIZER_HIDE_VAR(one); two = vzalloc(PAGE_SIZE); pr_info("Attempting vmalloc linear overflow ...\n"); diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index 898b3458b24a..56467f86a27c 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -297,6 +297,11 @@ * * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size */ +#if __has_attribute(__pass_dynamic_object_size__) +# define __pass_dynamic_object_size(type) __attribute__((__pass_dynamic_object_size__(type))) +#else +# define __pass_dynamic_object_size(type) +#endif #if __has_attribute(__pass_object_size__) # define __pass_object_size(type) __attribute__((__pass_object_size__(type))) #else diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index 7cad8bb031e9..c9de1f59ee80 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -90,10 +90,17 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) * size, rather than struct size), but there remain some stragglers using * type 0 that will be converted in the future. */ +#if __has_builtin(__builtin_dynamic_object_size) +#define POS __pass_dynamic_object_size(1) +#define POS0 __pass_dynamic_object_size(0) +#define __struct_size(p) __builtin_dynamic_object_size(p, 0) +#define __member_size(p) __builtin_dynamic_object_size(p, 1) +#else #define POS __pass_object_size(1) #define POS0 __pass_object_size(0) #define __struct_size(p) __builtin_object_size(p, 0) #define __member_size(p) __builtin_object_size(p, 1) +#endif #define __compiletime_lessthan(bounds, length) ( \ __builtin_constant_p((bounds) < (length)) && \ -- 2.11.0