Commit 439a1bca authored by Kees Cook's avatar Kees Cook
Browse files

fortify: Use __builtin_dynamic_object_size() when available 



Since the commits starting with c37495d6 ("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 <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Tom Rix <trix@redhat.com>
Cc: linux-hardening@vger.kernel.org
Cc: llvm@lists.linux.dev
Reviewed-by: Miguel Ojeda <ojeda@kernel.org> # include/linux/compiler_attributes.h
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent b2ba00c2

drivers/misc/lkdtm/heap.c

+1 −0
Original line number Diff line number Diff line
@@ -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");

include/linux/compiler_attributes.h

+5 −0
Original line number Diff line number Diff line
@@ -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

include/linux/fortify-string.h

+7 −0
Original line number Diff line number Diff line
@@ -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)) &&	\