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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id j7sm4812325pjz.12.2019.11.19.17.06.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Nov 2019 17:06:41 -0800 (PST) From: Kees Cook To: Andrey Ryabinin Cc: Kees Cook , Elena Petrova , Alexander Potapenko , Dmitry Vyukov , Linus Torvalds , Dan Carpenter , "Gustavo A. R. Silva" , Arnd Bergmann , Ard Biesheuvel , Andrew Morton , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH 2/3] ubsan: Split "bounds" checker from other options Date: Tue, 19 Nov 2019 17:06:35 -0800 Message-Id: <20191120010636.27368-3-keescook@chromium.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191120010636.27368-1-keescook@chromium.org> References: <20191120010636.27368-1-keescook@chromium.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In order to do kernel builds with the bounds checker individually available, introduce CONFIG_UBSAN_BOUNDS, with the remaining options under CONFIG_UBSAN_MISC. For example, using this, we can start to expand the coverage syzkaller is providing. Right now, all of UBSan is disabled for syzbot builds because taken as a whole, it is too noisy. This will let us focus on one feature at a time. For the bounds checker specifically, this provides a mechanism to eliminate an entire class of array overflows with close to zero performance overhead (I cannot measure a difference). In my (mostly) defconfig, enabling bounds checking adds ~4200 checks to the kernel. Performance changes are in the noise, likely due to the branch predictors optimizing for the non-fail path. Some notes on the bounds checker: - it does not instrument {mem,str}*()-family functions, it only instruments direct indexed accesses (e.g. "foo[i]"). Dealing with the {mem,str}*()-family functions is a work-in-progress around CONFIG_FORTIFY_SOURCE[1]. - it ignores flexible array members, including the very old single byte (e.g. "int foo[1];") declarations. (Note that GCC's implementation appears to ignore _all_ trailing arrays, but Clang only ignores empty, 0, and 1 byte arrays[2].) [1] https://github.com/KSPP/linux/issues/6 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92589 Suggested-by: Elena Petrova Signed-off-by: Kees Cook --- lib/Kconfig.ubsan | 19 +++++++++++++++++++ scripts/Makefile.ubsan | 7 ++++++- 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index d69e8b21ebae..f5ed2dceef30 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -22,6 +22,25 @@ config UBSAN_TRAP can just issue a trap. This reduces the kernel size overhead but turns all warnings into full thread-killing exceptions. +config UBSAN_BOUNDS + bool "Perform array bounds checking" + depends on UBSAN + default UBSAN + help + This option enables detection of direct out of bounds array + accesses, where the array size is known at compile time. Note + that this does not protect character array overflows due to + bad calls to the {str,mem}*cpy() family of functions. + +config UBSAN_MISC + bool "Enable all other Undefined Behavior sanity checks" + depends on UBSAN + default UBSAN + help + This option enables all sanity checks that don't have their + own Kconfig options. Disable this if you only want to have + individually selected checks. + config UBSAN_SANITIZE_ALL bool "Enable instrumentation for the entire kernel" depends on UBSAN diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan index 668a91510bfe..5b15bc425ec9 100644 --- a/scripts/Makefile.ubsan +++ b/scripts/Makefile.ubsan @@ -5,14 +5,19 @@ ifdef CONFIG_UBSAN_ALIGNMENT CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment) endif +ifdef CONFIG_UBSAN_BOUNDS + CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds) +endif + +ifdef CONFIG_UBSAN_MISC CFLAGS_UBSAN += $(call cc-option, -fsanitize=shift) CFLAGS_UBSAN += $(call cc-option, -fsanitize=integer-divide-by-zero) CFLAGS_UBSAN += $(call cc-option, -fsanitize=unreachable) CFLAGS_UBSAN += $(call cc-option, -fsanitize=signed-integer-overflow) - CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds) CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size) CFLAGS_UBSAN += $(call cc-option, -fsanitize=bool) CFLAGS_UBSAN += $(call cc-option, -fsanitize=enum) +endif ifdef CONFIG_UBSAN_TRAP CFLAGS_UBSAN += $(call cc-option, -fsanitize-undefined-trap-on-error) -- 2.17.1