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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 l0_%=; // r1 >= 0 implies r0 >= 4 // verifier couldn't propagate bounds back to r0 if r0 != 0 goto l0_%=; r0 /= 0; // Verifier thinks this is reachable l0_%=: Similar limitation exists for 32-bit registers. With this change, the verifier can now track negative deltas in reg->off enabling bound propagation for the above pattern. For alu32, we make sure the destination register has the upper 32 bits as 0s before creating the link. BPF_ADD_CONST is split into BPF_ADD_CONST64 and BPF_ADD_CONST32, the latter is used in case of alu32 and sync_linked_regs uses this to zext the result if known_reg has this flag. Signed-off-by: Puranjay Mohan <puranjay@kernel.org> Acked-by: Eduard Zingerman <eddyz87@gmail.com> Link: https://lore.kernel.org/r/20260204151741.2678118-2-puranjay@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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