Verifier linked reg neg #10651
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Verifier linked reg neg #10651
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Extend the linked register tracking to support: 1. Negative offsets via BPF_ADD (e.g., r1 += -4) 2. BPF_SUB operations (e.g., r1 -= 4), which is treated as r1 += -4 Previously, the verifier only tracked positive constant deltas between linked registers using BPF_ADD. This limitation meant patterns like: r1 = r0 r1 += -4 if r1 s>= 0 goto ... // r1 >= 0 implies r0 >= 4 // verifier couldn't propagate bounds back to r0 With this change, the verifier can now track negative deltas in reg->off (which is already s32), enabling bound propagation for the above pattern. The changes include: - Accept BPF_SUB in addition to BPF_ADD - Change overflow check from val > (u32)S32_MAX to checking if val fits in s32 range: (s64)val != (s64)(s32)val - For BPF_SUB, negate the offset with a guard against S32_MIN overflow - Keep !alu32 restriction as 32-bit ALU has known issues with upper bits Signed-off-by: Puranjay Mohan <[email protected]>
…ffsets Add tests for linked register tracking with negative offsets and BPF_SUB: Success cases (64-bit ALU, tracking works): - scalars_neg: r1 += -4 with signed comparison - scalars_neg_sub: r1 -= 4 with signed comparison - scalars_pos: r1 += 4 with unsigned comparison - scalars_sub_neg_imm: r1 -= -4 (equivalent to r1 += 4) Failure cases (tracking disabled, documents limitations): - scalars_neg_alu32_add: 32-bit ADD not tracked - scalars_neg_alu32_sub: 32-bit SUB not tracked - scalars_double_add: Double ADD clears ID Large delta tests (verifies 64-bit arithmetic in sync_linked_regs): - scalars_sync_delta_overflow: S32_MIN offset - scalars_sync_delta_overflow_large_range: S32_MAX offset Signed-off-by: Puranjay Mohan <[email protected]>
Update the expected regex pattern for the sub64_partial_overflow test. With BPF_SUB now supporting linked register tracking, the verifier output shows R3=scalar(id=1-1) instead of R3=scalar() because r3 is now tracked as linked to r0 with an offset of -1. Signed-off-by: Puranjay Mohan <[email protected]>
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