Unpoison fiber stack before each resume to fix ASan false positives#100281
Merged
alexey-milovidov merged 1 commit intomasterfrom Mar 21, 2026
Merged
Unpoison fiber stack before each resume to fix ASan false positives#100281alexey-milovidov merged 1 commit intomasterfrom
alexey-milovidov merged 1 commit intomasterfrom
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ASan's use-after-scope detection poisons real stack memory when local variables go out of scope. On fiber stacks managed by `makecontext`/`swapcontext`, this poisoning persists across context switches (yield/resume), causing false positives when the same stack addresses are reused by new frames in subsequent fiber resumes - notably during exception unwinding in `_Unwind_Resume`. The fix: call `ASAN_UNPOISON_MEMORY_REGION` on the entire fiber stack before each `Fiber::resume`, clearing any stale scope poisoning. This is complementary to the `__sanitizer_start_switch_fiber` / `__sanitizer_finish_switch_fiber` annotations in boost::context, which only manage the fake stack (for use-after-return), not real stack poisoning (for use-after-scope). See google/sanitizers#189 Example: https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=100041&sha=e3d5fc0647f84f316414376a48aa9ffbf8565b07&name_0=PR&name_1=AST%20fuzzer%20%28arm_asan_ubsan%29 Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
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Workflow [PR], commit [1f870bb] Summary: ✅ AI ReviewSummaryThis PR addresses ASan false positives on fiber stacks by unpoisoning the allocated fiber stack before each ClickHouse Rules
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PR changed lines: PR changed-lines coverage: 100.00% (15/15, 0 noise lines excluded) |
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| void * stack_base = nullptr; | ||
| size_t stack_allocation_size = 0; |
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Interesting why it does not trigger that the variable is not used warning
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ASan's
use-after-scopedetection poisons real stack memory when local variables go out of scope. On fiber stacks managed bymakecontext/swapcontext, this poisoning persists across context switches (yield/resume), causing false positives when the same stack addresses are reused by new frames in subsequent fiber resumes — notably during exception unwinding in_Unwind_Resume.The fix: call
ASAN_UNPOISON_MEMORY_REGIONon the entire fiber stack before eachFiber::resume, clearing any stale scope poisoning. This is complementary to the__sanitizer_start_switch_fiber/__sanitizer_finish_switch_fiberannotations in boost::context, which only manage the fake stack (for use-after-return), not real stack poisoning (for use-after-scope).See google/sanitizers#189
Example failure: https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=100041&sha=e3d5fc0647f84f316414376a48aa9ffbf8565b07&name_0=PR&name_1=AST%20fuzzer%20%28arm_asan_ubsan%29
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