bpf: Skip bounds adjustment for conditional jumps on same register #10092
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When conditional jumps are performed on the same register (e.g., r0 <= r0, r0 > r0, r0 < r0) where the register holds a scalar with range, the verifier incorrectly attempts to adjust the register's min/max bounds. This leads to invalid range bounds and triggers a BUG warning: verifier bug: REG INVARIANTS VIOLATION (true_reg1): range bounds violation u64=[0x1, 0x0] s64=[0x1, 0x0] u32=[0x1, 0x0] s32=[0x1, 0x0] var_off=(0x0, 0x0) WARNING: CPU: 0 PID: 92 at kernel/bpf/verifier.c:2731 reg_bounds_sanity_check+0x163/0x220 Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:reg_bounds_sanity_check+0x163/0x220 Call Trace: <TASK> reg_set_min_max+0xf7/0x1d0 check_cond_jmp_op+0x57b/0x1730 ? print_bpf_insn+0x3d5/0xa50 do_check_common+0x33ac/0x33c0 ... The root cause is in regs_refine_cond_op() where BPF_JLT/BPF_JSLT operations adjust both min/max bounds on the same register, causing invalid bounds. Since comparing a register with itself should not change its bounds (the comparison result is always known: r0 == r0 is always true, r0 < r0 is always false), the bounds adjustment is unnecessary. Fix this by: 1. Enhance is_branch_taken() and is_scalar_branch_taken() to properly handle branch direction computation for same register comparisons across all BPF jump operations 2. For unknown branch directions (e.g., BPF_JSET), add early return in reg_set_min_max() to avoid bounds adjustment on the same register The fix ensures that unnecessary bounds adjustments are skipped, preventing the verifier bug while maintaining correct branch direction analysis. Reported-by: Kaiyan Mei <[email protected]> Reported-by: Yinhao Hu <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Fixes: 0df1a55 ("bpf: Warn on internal verifier errors") Signed-off-by: KaFai Wan <[email protected]>
Add a test to verify that conditional jumps using the BPF_JGT opcode on the same register (e.g., "if r0 > r0") do not trigger verifier BUG warnings when the register contains a scalar value with range information. Signed-off-by: KaFai Wan <[email protected]>
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Upstream branch: e758657 |
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Pull request for series with
subject: bpf: Skip bounds adjustment for conditional jumps on same register
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1015700