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: 0df1a55afa83 ("bpf: Warn on internal verifier errors") Signed-off-by: KaFai Wan <[email protected]> --- kernel/bpf/verifier.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 6d175849e57a..653fa96ed0df 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16037,6 +16037,12 @@ static int is_scalar_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_sta } break; case BPF_JSET: + if (reg1 == reg2) { + if (tnum_is_const(t1)) + return t1.value != 0; + else + return (smin1 <= 0 && smax1 >= 0) ? -1 : 1; + } if (!is_reg_const(reg2, is_jmp32)) { swap(reg1, reg2); swap(t1, t2); @@ -16172,6 +16178,25 @@ static int is_pkt_ptr_branch_taken(struct bpf_reg_state *dst_reg, static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2, u8 opcode, bool is_jmp32) { + if (reg1 == reg2) { + switch (opcode) { + case BPF_JGE: + case BPF_JLE: + case BPF_JSGE: + case BPF_JSLE: + case BPF_JEQ: + return 1; + case BPF_JGT: + case BPF_JLT: + case BPF_JSGT: + case BPF_JSLT: + case BPF_JNE: + return 0; + default: + break; + } + } + if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && !is_jmp32) return is_pkt_ptr_branch_taken(reg1, reg2, opcode); @@ -16429,6 +16454,13 @@ static int reg_set_min_max(struct bpf_verifier_env *env, if (false_reg1->type != SCALAR_VALUE || false_reg2->type != SCALAR_VALUE) return 0; + /* We compute branch direction for same registers in is_branch_taken() and + * is_scalar_branch_taken(). For unknown branch directions (e.g., BPF_JSET) + * on the same registers, we don't need to adjusts the min/max values. + */ + if (false_reg1 == false_reg2) + return 0; + /* fallthrough (FALSE) branch */ regs_refine_cond_op(false_reg1, false_reg2, rev_opcode(opcode), is_jmp32); reg_bounds_sync(false_reg1); -- 2.43.0
