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ubsan: Tighten UBSAN_BOUNDS on GCC

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The use of -fsanitize=bounds on GCC will ignore some trailing arrays,
leaving a gap in coverage. Switch to using -fsanitize=bounds-strict to
match Clang's stricter behavior.

Cc: Marco Elver <elver@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Tom Rix <trix@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: linux-kbuild@vger.kernel.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230405022356.gonna.338-kees@kernel.org
This commit is contained in:
Kees Cook 2023-04-04 19:23:59 -07:00
parent f1fcbaa18b
commit 2d47c6956a
2 changed files with 31 additions and 25 deletions
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54
lib/Kconfig.ubsan
View File

@ -27,16 +27,29 @@ config UBSAN_TRAP
the system. For some system builders this is an acceptable
trade-off.
config CC_HAS_UBSAN_BOUNDS
def_bool $(cc-option,-fsanitize=bounds)
config CC_HAS_UBSAN_BOUNDS_STRICT
def_bool $(cc-option,-fsanitize=bounds-strict)
help
The -fsanitize=bounds-strict option is only available on GCC,
but uses the more strict handling of arrays that includes knowledge
of flexible arrays, which is comparable to Clang's regular
-fsanitize=bounds.
config CC_HAS_UBSAN_ARRAY_BOUNDS
def_bool $(cc-option,-fsanitize=array-bounds)
help
Under Clang, the -fsanitize=bounds option is actually composed
of two more specific options, -fsanitize=array-bounds and
-fsanitize=local-bounds. However, -fsanitize=local-bounds can
only be used when trap mode is enabled. (See also the help for
CONFIG_LOCAL_BOUNDS.) Explicitly check for -fsanitize=array-bounds
so that we can build up the options needed for UBSAN_BOUNDS
with or without UBSAN_TRAP.
config UBSAN_BOUNDS
bool "Perform array index bounds checking"
default UBSAN
depends on CC_HAS_UBSAN_ARRAY_BOUNDS || CC_HAS_UBSAN_BOUNDS
depends on CC_HAS_UBSAN_ARRAY_BOUNDS || CC_HAS_UBSAN_BOUNDS_STRICT
help
This option enables detection of directly indexed out of bounds
array accesses, where the array size is known at compile time.
@ -44,33 +57,26 @@ config UBSAN_BOUNDS
to the {str,mem}*cpy() family of functions (that is addressed
by CONFIG_FORTIFY_SOURCE).
config UBSAN_ONLY_BOUNDS
def_bool CC_HAS_UBSAN_BOUNDS && !CC_HAS_UBSAN_ARRAY_BOUNDS
depends on UBSAN_BOUNDS
config UBSAN_BOUNDS_STRICT
def_bool UBSAN_BOUNDS && CC_HAS_UBSAN_BOUNDS_STRICT
help
This is a weird case: Clang's -fsanitize=bounds includes
-fsanitize=local-bounds, but it's trapping-only, so for
Clang, we must use -fsanitize=array-bounds when we want
traditional array bounds checking enabled. For GCC, we
want -fsanitize=bounds.
GCC's bounds sanitizer. This option is used to select the
correct options in Makefile.ubsan.
config UBSAN_ARRAY_BOUNDS
def_bool CC_HAS_UBSAN_ARRAY_BOUNDS
depends on UBSAN_BOUNDS
def_bool UBSAN_BOUNDS && CC_HAS_UBSAN_ARRAY_BOUNDS
help
Clang's array bounds sanitizer. This option is used to select
the correct options in Makefile.ubsan.
config UBSAN_LOCAL_BOUNDS
bool "Perform array local bounds checking"
depends on UBSAN_TRAP
depends on $(cc-option,-fsanitize=local-bounds)
def_bool UBSAN_ARRAY_BOUNDS && UBSAN_TRAP
help
This option enables -fsanitize=local-bounds which traps when an
exception/error is detected. Therefore, it may only be enabled
with CONFIG_UBSAN_TRAP.
Enabling this option detects errors due to accesses through a
pointer that is derived from an object of a statically-known size,
where an added offset (which may not be known statically) is
out-of-bounds.
This option enables Clang's -fsanitize=local-bounds which traps
when an access through a pointer that is derived from an object
of a statically-known size, where an added offset (which may not
be known statically) is out-of-bounds. Since this option is
trap-only, it depends on CONFIG_UBSAN_TRAP.
config UBSAN_SHIFT
bool "Perform checking for bit-shift overflows"

2
scripts/Makefile.ubsan
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@ -2,7 +2,7 @@
# Enable available and selected UBSAN features.
ubsan-cflags-$(CONFIG_UBSAN_ALIGNMENT) += -fsanitize=alignment
ubsan-cflags-$(CONFIG_UBSAN_ONLY_BOUNDS) += -fsanitize=bounds
ubsan-cflags-$(CONFIG_UBSAN_BOUNDS_STRICT) += -fsanitize=bounds-strict
ubsan-cflags-$(CONFIG_UBSAN_ARRAY_BOUNDS) += -fsanitize=array-bounds
ubsan-cflags-$(CONFIG_UBSAN_LOCAL_BOUNDS) += -fsanitize=local-bounds
ubsan-cflags-$(CONFIG_UBSAN_SHIFT) += -fsanitize=shift