- Dec 10, 2021
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Marco Elver authored
GCC 11 has introduced a new warning option, -Wtsan [1], to warn about unsupported operations in the TSan runtime. But KCSAN != TSan runtime, so none of the warnings apply. [1] https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html Ignore the warnings. Currently the warning only fires in the test for __atomic_thread_fence(): kernel/kcsan/kcsan_test.c: In function ‘test_atomic_builtins’: kernel/kcsan/kcsan_test.c:1234:17: warning: ‘atomic_thread_fence’ is not supported with ‘-fsanitize=thread’ [-Wtsan] 1234 | __atomic_thread_fence(__ATOMIC_SEQ_CST); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ which exists to ensure the KCSAN runtime keeps supporting the builtin instrumentation. Signed-off-by:
Marco Elver <elver@google.com> Signed-off-by:
Paul E. McKenney <paulmck@kernel.org>
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Marco Elver authored
Add support for modeling a subset of weak memory, which will enable detection of a subset of data races due to missing memory barriers. KCSAN's approach to detecting missing memory barriers is based on modeling access reordering, and enabled if `CONFIG_KCSAN_WEAK_MEMORY=y`, which depends on `CONFIG_KCSAN_STRICT=y`. The feature can be enabled or disabled at boot and runtime via the `kcsan.weak_memory` boot parameter. Each memory access for which a watchpoint is set up, is also selected for simulated reordering within the scope of its function (at most 1 in-flight access). We are limited to modeling the effects of "buffering" (delaying the access), since the runtime cannot "prefetch" accesses (therefore no acquire modeling). Once an access has been selected for reordering, it is checked along every other access until the end of the function scope. If an appropriate memory barrier is encountered, the access will no longer be considered for reordering. When the result of a memory operation should be ordered by a barrier, KCSAN can then detect data races where the conflict only occurs as a result of a missing barrier due to reordering accesses. Suggested-by:
Dmitry Vyukov <dvyukov@google.com> Signed-off-by:
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- Sep 24, 2020
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Masahiro Yamada authored
Move CFLAGS_KASAN*, CFLAGS_UBSAN, CFLAGS_KCSAN to Makefile.kasan, Makefile.ubsan, Makefile.kcsan, respectively. This commit also avoids the same -fsanitize=* flags being added to CFLAGS_UBSAN multiple times. Prior to this commit, the ubsan flags were appended by the '+=' operator, without any initialization. Some build targets such as 'make bindeb-pkg' recurses to the top Makefile, and ended up with adding the same flags to CFLAGS_UBSAN twice. Clear CFLAGS_UBSAN with ':=' to make it a simply expanded variable. This is better than a recursively expanded variable, which evaluates $(call cc-option, ...) multiple times before Kbuild starts descending to subdirectories. Signed-off-by:
Masahiro Yamada <masahiroy@kernel.org> Acked-by:
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- Aug 24, 2020
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Marco Elver authored
Add support for compounded read-write instrumentation if supported by the compiler. Adds the necessary instrumentation functions, and a new type which is used to generate a more descriptive report. Furthermore, such compounded memory access instrumentation is excluded from the "assume aligned writes up to word size are atomic" rule, because we cannot assume that the compiler emits code that is atomic for compound ops. LLVM/Clang added support for the feature in: https://github.com/llvm/llvm-project/commit/785d41a261d136b64ab6c15c5d35f2adc5ad53e3 The new instrumentation is emitted for sets of memory accesses in the same basic block to the same address with at least one read appearing before a write. These typically result from compound operations such as ++, --, +=, -=, |=, &=, etc. but also equivalent forms such as "var = var + 1". Where the compiler determines that it is equivalent to emit a call to a single __tsan_read_write instead of separate __tsan_read and __tsan_write, we can then benefit from improved performance and better reporting for such access patterns. The new reports now show that the ops are both reads and writes, for example: read-write to 0xffffffff90548a38 of 8 bytes by task 143 on cpu 3: test_kernel_rmw_array+0x45/0xa0 access_thread+0x71/0xb0 kthread+0x21e/0x240 ret_from_fork+0x22/0x30 read-write to 0xffffffff90548a38 of 8 bytes by task 144 on cpu 2: test_kernel_rmw_array+0x45/0xa0 access_thread+0x71/0xb0 kthread+0x21e/0x240 ret_from_fork+0x22/0x30 Acked-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by:
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- Aug 09, 2020
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Masahiro Yamada authored
Currently, the top Makefile includes all of scripts/Makefile.<feature> even if the associated CONFIG option is disabled. Do not include unneeded Makefiles in order to slightly optimize the parse stage. Include $(include-y), and ignore $(include-). Signed-off-by:
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- Jun 29, 2020
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Marco Elver authored
GCC version 11 recently implemented all requirements to correctly support KCSAN: 1. Correct no_sanitize-attribute inlining behaviour: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=4089df8ef4a63126b0774c39b6638845244c20d2 2. --param=tsan-distinguish-volatile https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=ab2789ec507a94f1a75a6534bca51c7b39037ce0 3. --param=tsan-instrument-func-entry-exit https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=06712fc68dc9843d9af7c7ac10047f49d305ad76 Therefore, we can re-enable GCC for KCSAN, and document the new compiler requirements. Signed-off-by:
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- Jun 11, 2020
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Marco Elver authored
Clang (unlike GCC) removes reads before writes with matching addresses in the same basic block. This is an optimization for TSAN, since writes will always cause conflict if the preceding read would have. However, for KCSAN we cannot rely on this option, because we apply several special rules to writes, in particular when the KCSAN_ASSUME_PLAIN_WRITES_ATOMIC option is selected. To avoid missing potential data races, pass the -tsan-instrument-read-before-write option to Clang if it is available [1]. [1] https://github.com/llvm/llvm-project/commit/151ed6aa38a3ec6c01973b35f684586b6e1c0f7e Signed-off-by:
Borislav Petkov <bp@suse.de> Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Acked-by:
Will Deacon <will@kernel.org> Link: https://lkml.kernel.org/r/20200521142047.169334-5-elver@google.com
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Marco Elver authored
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:
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Marco Elver authored
To avoid inserting __tsan_func_{entry,exit}, add option if supported by compiler. Currently only Clang can be told to not emit calls to these functions. It is safe to not emit these, since KCSAN does not rely on them. Note that, if we disable __tsan_func_{entry,exit}(), we need to disable tail-call optimization in sanitized compilation units, as otherwise we may skip frames in the stack trace; in particular when the tail called function is one of the KCSAN's runtime functions, and a report is generated, we might miss the function where the actual access occurred. Since __tsan_func_{entry,exit}() insertion effectively disabled tail-call optimization, there should be no observable change. This was caught and confirmed with kcsan-test & UNWINDER_ORC. Signed-off-by:
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- Nov 16, 2019
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Marco Elver authored
Kernel Concurrency Sanitizer (KCSAN) is a dynamic data-race detector for kernel space. KCSAN is a sampling watchpoint-based data-race detector. See the included Documentation/dev-tools/kcsan.rst for more details. This patch adds basic infrastructure, but does not yet enable KCSAN for any architecture. Signed-off-by:
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