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Message-Id: <20230405022356.gonna.338-kees@kernel.org>
Date: Tue, 4 Apr 2023 19:23:59 -0700
From: Kees Cook <keescook@...omium.org>
To: Marco Elver <elver@...gle.com>
Cc: Kees Cook <keescook@...omium.org>,
Masahiro Yamada <masahiroy@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Miroslav Benes <mbenes@...e.cz>, linux-kbuild@...r.kernel.org,
llvm@...ts.linux.dev, Sudip Mukherjee <sudipm.mukherjee@...il.com>,
Lukas Bulwahn <lukas.bulwahn@...il.com>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v2] ubsan: Tighten UBSAN_BOUNDS on GCC
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@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Nicolas Schier <nicolas@...sle.eu>
Cc: Tom Rix <trix@...hat.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Miroslav Benes <mbenes@...e.cz>
Cc: linux-kbuild@...r.kernel.org
Cc: llvm@...ts.linux.dev
Signed-off-by: Kees Cook <keescook@...omium.org>
---
v2: improve help text (nathan)
v1: https://lore.kernel.org/lkml/20230302225444.never.053-kees@kernel.org/
---
lib/Kconfig.ubsan | 56 +++++++++++++++++++++++-------------------
scripts/Makefile.ubsan | 2 +-
2 files changed, 32 insertions(+), 26 deletions(-)
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index fd15230a703b..65d8bbcba438 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -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 $(cc-option,-fsanitize=local-bounds)
- help
- This option enables -fsanitize=local-bounds which traps when an
- exception/error is detected. Therefore, it may only be enabled
- with CONFIG_UBSAN_TRAP.
-
- Enabling this option detects errors due to accesses through a
- pointer that is derived from an object of a statically-known size,
- where an added offset (which may not be known statically) is
- out-of-bounds.
+ def_bool UBSAN_ARRAY_BOUNDS && UBSAN_TRAP
+ help
+ This option enables Clang's -fsanitize=local-bounds which traps
+ when an access through a pointer that is derived from an object
+ of a statically-known size, where an added offset (which may not
+ be known statically) is out-of-bounds. Since this option is
+ trap-only, it depends on CONFIG_UBSAN_TRAP.
config UBSAN_SHIFT
bool "Perform checking for bit-shift overflows"
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 7099c603ff0a..4749865c1b2c 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -2,7 +2,7 @@
# Enable available and selected UBSAN features.
ubsan-cflags-$(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
--
2.34.1
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