ubsan: Tighten UBSAN_BOUNDS on GCC
Subsystems (3)
PATCH 1/1 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 <[email protected]>
Cc Masahiro Yamada <[email protected]>
Cc Nathan Chancellor <[email protected]>
Cc Nick Desaulniers <[email protected]>
Cc Nicolas Schier <[email protected]>
Cc Tom Rix <[email protected]>
Cc Josh Poimboeuf <[email protected]>
Cc Miroslav Benes <[email protected]>
Signed-off-by Kees Cook <[email protected]>
--- lib/Kconfig.ubsan | 54 +++++++++++++++++++++++------------------- scripts/Makefile.ubsan | 2 +- 2 files changed, 30 insertions(+), 26 deletions(-)
lib/Kconfig.ubsan +29 -25
@@ -27,16 +27,27 @@ 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 + The -fsanitize=array-bounds option is only available on Clang, + and 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.) 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 +55,26 @@ 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 $(cc-option,-fsanitize=local-bounds) - help - This option enables -fsanitize=local-bounds which traps when an - exception/error is detected. Therefore, it may only be enabled - with CONFIG_UBSAN_TRAP. - - Enabling this option detects errors due to accesses through a - pointer that is derived from an object of a statically-known size, - where an added offset (which may not be known statically) is - out-of-bounds. + def_bool UBSAN_ARRAY_BOUNDS && UBSAN_TRAP + help + This option enables Clang's -fsanitize=local-bounds which traps + when an access through a pointer that is derived from an object + of a statically-known size, where an added offset (which may not + be known statically) is out-of-bounds. Since this option is + trap-only, it depends on CONFIG_UBSAN_TRAP. config UBSAN_SHIFT bool "Perform checking for bit-shift overflows"
scripts/Makefile.ubsan +1 -1
@@ -2,7 +2,7 @@ # Enable available and selected UBSAN features. ubsan-cflags-$(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
Signature · 1 line
2.34.1
Nathan Chancellor
maintainerQuoted 36 lines · Kees Cook
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 <[email protected]>Cc Masahiro Yamada <[email protected]>Cc Nathan Chancellor <[email protected]>Cc Nick Desaulniers <[email protected]>Cc Nicolas Schier <[email protected]>Cc Tom Rix <[email protected]>Cc Josh Poimboeuf <[email protected]>Cc Miroslav Benes <[email protected]>Signed-off-by Kees Cook <[email protected]>--- lib/Kconfig.ubsan | 54 +++++++++++++++++++++++------------------- scripts/Makefile.ubsan | 2 +- 2 files changed, 30 insertions(+), 26 deletions(-)lib/Kconfig.ubsan +6
-2@@ -27,16 +27,27 @@ 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
lib/Kconfig.ubsan config UBSAN_TRAP · line 45
Quoted 10 lines
lib/Kconfig.ubsan +7
-0+ -fsanitize=bounds. config CC_HAS_UBSAN_ARRAY_BOUNDS def_bool $(cc-option,-fsanitize=array-bounds) + help + The -fsanitize=array-bounds option is only available on Clang, + and 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.)
The first sentence does not read right to me, you have array-bounds twice. I think the first one wants to be just bounds?
Quoted 73 lines
lib/Kconfig.ubsan +16
-23config 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 +55,26 @@ 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 $(cc-option,-fsanitize=local-bounds) - help - This option enables -fsanitize=local-bounds which traps when an - exception/error is detected. Therefore, it may only be enabled - with CONFIG_UBSAN_TRAP. - - Enabling this option detects errors due to accesses through a - pointer that is derived from an object of a statically-known size, - where an added offset (which may not be known statically) is - out-of-bounds. + def_bool UBSAN_ARRAY_BOUNDS && UBSAN_TRAP + help + This option enables Clang's -fsanitize=local-bounds which traps + when an access through a pointer that is derived from an object + of a statically-known size, where an added offset (which may not + be known statically) is out-of-bounds. Since this option is + trap-only, it depends on CONFIG_UBSAN_TRAP. config UBSAN_SHIFT bool "Perform checking for bit-shift overflows"scripts/Makefile.ubsan +1
-1@@ -2,7 +2,7 @@ # Enable available and selected UBSAN features. ubsan-cflags-$(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=shiftSignature · 1 line
2.34.1
Quoted 13 lines · Nathan Chancellor
lib/Kconfig.ubsan config UBSAN_TRAP · line 45
Quoted 9 lines · Kees Cook
[...]
configCC_HAS_UBSAN_ARRAY_BOUNDSlib/Kconfig.ubsan +6
-0def_bool $(cc-option,-fsanitize=array-bounds) + help + The -fsanitize=array-bounds option is only available on Clang, + and 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.)The first sentence does not read right to me, you have array-bounds twice. I think the first one wants to be just bounds?
Oops, yes. I rewrote that a few times and seem to have gotten lost. I think it is better written as:
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.
Signature · 1 line
Kees Cook