Clamp 1D attention mask_index to valid bounds#29449
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Use std::clamp for end_position and start_position in the 1D mask_index branch of attention_helper.h so out-of-range mask values cannot drive out-of-bounds writes into the mask buffer. Add AttentionMaskIndex1DClampOOB test covering an over-large end_position and a negative start_position.
apsonawane
approved these changes
Jul 2, 2026
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PR: Clamp 1D attention mask_index to valid bounds
Description
The CPU attention helper translates a 1D
mask_index(right-side end position, andoptionally a left-side start position) into per-token mask-fill loop bounds. The
existing
std::max(0, std::min(...))clamp was correct but verbose; this PR replaces itwith
std::clampand adds a regression test that exercises out-of-range mask values.This hardens the kernel against out-of-bounds writes when callers supply mask positions
outside
[0, all_sequence_length].Summary of Changes
Bounds clamping
onnxruntime/contrib_ops/cpu/bert/attention_helper.hstd::clamp(static_cast<int>(mask_index[...]), 0, all_sequence_length)for bothend_positionandstart_positionin the 1Dmask_indexbranch ofPrepareMask.Test coverage
onnxruntime/test/contrib_ops/attention_op_test.ccAttentionMaskIndex1DClampOOB, covering an over-largeend_position(999) and a negativestart_position(-5). Both clamp cleanly and produce the fully-unmasked output.Testing
onnxruntime_test_all --gtest_filter='ContribOpAttentionTest.AttentionMaskIndex1DClampOOB'all_sequence_length)applies no right-side masking, and a negative start position applies no left-side
masking — matching a fully-unmasked sequence.
ContribOpAttentionTest.*cases continue to pass; behavior for in-rangemask values is unchanged.
Motivation and Context
end_position/start_positiondrive raw index loops into the mask buffer. Anunclamped value past
all_sequence_length(or a negative start) could otherwise stepoutside the intended range.
std::clampguarantees both stay within[0, all_sequence_length], preventing out-of-bounds writes with no behavior change forvalid inputs.
Checklist