Detection of some missing memory barriers has been on the KCSAN feature wishlist for some time: this series adds support for modeling a subset of weak memory as defined by the LKMM, which enables 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. 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. 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. Some more details and an example are captured in the updated <Documentation/dev-tools/kcsan.rst>. Some light fuzzing with the feature also resulted in a discussion [1] around an issue which appears to be allowed, but unlikely in practice. [1] https://lkml.kernel.org/r/YRo58c+JGOvec7tc@xxxxxxxxxxxxxxxx The first half of the series are core KCSAN changes, documentation updates, and test changes. The second half adds instrumentation to barriers, atomics, bitops, along with enabling barrier instrumentation for some currently uninstrumented subsystems. The last two patches are objtool changes to add the usual entries to the uaccess whitelist, but also instruct objtool to remove memory barrier instrumentation from noinstr code (on x86). --- v2: * Rewrite objtool patch after rebase to v5.16-rc1. * Note the reason in documentation that address or control dependencies do not require special handling. * Rename kcsan_atomic_release() to kcsan_atomic_builtin_memorder() to avoid confusion. * Define kcsan_noinstr as noinline if we rely on objtool nop'ing out calls, to avoid things like LTO inlining it. v1: https://lore.kernel.org/all/20211005105905.1994700-1-elver@xxxxxxxxxx/ Marco Elver (23): kcsan: Refactor reading of instrumented memory kcsan: Remove redundant zero-initialization of globals kcsan: Avoid checking scoped accesses from nested contexts kcsan: Add core support for a subset of weak memory modeling kcsan: Add core memory barrier instrumentation functions kcsan, kbuild: Add option for barrier instrumentation only kcsan: Call scoped accesses reordered in reports kcsan: Show location access was reordered to kcsan: Document modeling of weak memory kcsan: test: Match reordered or normal accesses kcsan: test: Add test cases for memory barrier instrumentation kcsan: Ignore GCC 11+ warnings about TSan runtime support kcsan: selftest: Add test case to check memory barrier instrumentation locking/barriers, kcsan: Add instrumentation for barriers locking/barriers, kcsan: Support generic instrumentation locking/atomics, kcsan: Add instrumentation for barriers asm-generic/bitops, kcsan: Add instrumentation for barriers x86/barriers, kcsan: Use generic instrumentation for non-smp barriers x86/qspinlock, kcsan: Instrument barrier of pv_queued_spin_unlock() mm, kcsan: Enable barrier instrumentation sched, kcsan: Enable memory barrier instrumentation objtool, kcsan: Add memory barrier instrumentation to whitelist objtool, kcsan: Remove memory barrier instrumentation from noinstr Documentation/dev-tools/kcsan.rst | 76 +++- arch/x86/include/asm/barrier.h | 10 +- arch/x86/include/asm/qspinlock.h | 1 + include/asm-generic/barrier.h | 54 ++- .../asm-generic/bitops/instrumented-atomic.h | 3 + .../asm-generic/bitops/instrumented-lock.h | 3 + include/linux/atomic/atomic-instrumented.h | 135 +++++- include/linux/kcsan-checks.h | 51 ++- include/linux/kcsan.h | 11 +- include/linux/sched.h | 3 + include/linux/spinlock.h | 2 +- init/init_task.c | 9 +- kernel/kcsan/Makefile | 2 + kernel/kcsan/core.c | 326 +++++++++++--- kernel/kcsan/kcsan_test.c | 416 ++++++++++++++++-- kernel/kcsan/report.c | 51 ++- kernel/kcsan/selftest.c | 141 ++++++ kernel/sched/Makefile | 7 +- lib/Kconfig.kcsan | 16 + mm/Makefile | 2 + scripts/Makefile.kcsan | 15 +- scripts/Makefile.lib | 5 + scripts/atomic/gen-atomic-instrumented.sh | 41 +- tools/objtool/check.c | 41 +- tools/objtool/include/objtool/elf.h | 2 +- 25 files changed, 1248 insertions(+), 175 deletions(-) -- 2.34.0.rc2.393.gf8c9666880-goog
