bpf: Skip bounds adjustment for conditional jumps on same register #6201
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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: 93 at kernel/bpf/verifier.c:2731 reg_bounds_sanity_check+0x163/0x220 Modules linked in: CPU: 0 UID: 0 PID: 93 Comm: repro-x-3 Tainted: G W 6.18.0-rc1-ge7586577b75f-dirty #218 PREEMPT(full) Tainted: [W]=WARN 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.part.0+0x1b1/0x360 check_cond_jmp_op+0x1195/0x1a60 do_check_common+0x33ac/0x33c0 ... The issue occurs in reg_set_min_max() function where bounds adjustment logic is applied even when both registers being compared are the same. Comparing a register with itself should not change its bounds since the comparison result is always known (e.g., r0 == r0 is always true, r0 < r0 is always false). Fix this by adding an early return in reg_set_min_max() when false_reg1 and false_reg2 point to the same register, skipping the unnecessary bounds adjustment that leads to the verifier bug. 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 case to verify that conditional jumps on the same register (e.g., JGT r0 > r0) do not trigger verifier BUG warnings when the register holds a scalar with range. Signed-off-by: KaFai Wan <[email protected]>
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Pull request for series with
subject: bpf: Skip bounds adjustment for conditional jumps on same register
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1014618