The following commit has been merged into the locking/kcsan branch of tip: Commit-ID: 4e23395b9e97562d12b87a330a2fca3bf10c8663 Gitweb: https://git.kernel.org/tip/4e23395b9e97562d12b87a330a2fca3bf10c8663 Author: Marco Elver <elver@xxxxxxxxxx> AuthorDate: Thu, 21 May 2020 16:20:39 +02:00 Committer: Borislav Petkov <bp@xxxxxxx> CommitterDate: Fri, 22 May 2020 14:46:02 +02:00 kcsan: Support distinguishing volatile accesses In the kernel, the "volatile" keyword is used in various concurrent contexts, whether in low-level synchronization primitives or for legacy reasons. If supported by the compiler, it will be assumed that aligned volatile accesses up to sizeof(long long) (matching compiletime_assert_rwonce_type()) are atomic. Recent versions of Clang [1] (GCC tentative [2]) can instrument volatile accesses differently. Add the option (required) to enable the instrumentation, and provide the necessary runtime functions. None of the updated compilers are widely available yet (Clang 11 will be the first release to support the feature). [1] https://github.com/llvm/llvm-project/commit/5a2c31116f412c3b6888be361137efd705e05814 [2] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html This change allows removing of any explicit checks in primitives such as READ_ONCE() and WRITE_ONCE(). [ bp: Massage commit message a bit. ] Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Acked-by: Will Deacon <will@xxxxxxxxxx> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20200521142047.169334-4-elver@xxxxxxxxxx --- kernel/kcsan/core.c | 43 +++++++++++++++++++++++++++++++++++++++++- scripts/Makefile.kcsan | 5 ++++- 2 files changed, 47 insertions(+), 1 deletion(-) diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index a73a66c..15f6794 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -790,6 +790,49 @@ void __tsan_write_range(void *ptr, size_t size) EXPORT_SYMBOL(__tsan_write_range); /* + * Use of explicit volatile is generally disallowed [1], however, volatile is + * still used in various concurrent context, whether in low-level + * synchronization primitives or for legacy reasons. + * [1] https://lwn.net/Articles/233479/ + * + * We only consider volatile accesses atomic if they are aligned and would pass + * the size-check of compiletime_assert_rwonce_type(). + */ +#define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ + void __tsan_volatile_read##size(void *ptr) \ + { \ + const bool is_atomic = size <= sizeof(long long) && \ + IS_ALIGNED((unsigned long)ptr, size); \ + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ + return; \ + check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \ + } \ + EXPORT_SYMBOL(__tsan_volatile_read##size); \ + void __tsan_unaligned_volatile_read##size(void *ptr) \ + __alias(__tsan_volatile_read##size); \ + EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ + void __tsan_volatile_write##size(void *ptr) \ + { \ + const bool is_atomic = size <= sizeof(long long) && \ + IS_ALIGNED((unsigned long)ptr, size); \ + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ + return; \ + check_access(ptr, size, \ + KCSAN_ACCESS_WRITE | \ + (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \ + } \ + EXPORT_SYMBOL(__tsan_volatile_write##size); \ + void __tsan_unaligned_volatile_write##size(void *ptr) \ + __alias(__tsan_volatile_write##size); \ + EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) + +DEFINE_TSAN_VOLATILE_READ_WRITE(1); +DEFINE_TSAN_VOLATILE_READ_WRITE(2); +DEFINE_TSAN_VOLATILE_READ_WRITE(4); +DEFINE_TSAN_VOLATILE_READ_WRITE(8); +DEFINE_TSAN_VOLATILE_READ_WRITE(16); + +/* * The below are not required by KCSAN, but can still be emitted by the * compiler. */ diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan index 20337a7..75d2942 100644 --- a/scripts/Makefile.kcsan +++ b/scripts/Makefile.kcsan @@ -9,7 +9,10 @@ else cc-param = --param -$(1) endif +# Keep most options here optional, to allow enabling more compilers if absence +# of some options does not break KCSAN nor causes false positive reports. CFLAGS_KCSAN := -fsanitize=thread \ - $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) + $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \ + $(call cc-param,tsan-distinguish-volatile=1) endif # CONFIG_KCSAN
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