| Message ID | 20230307220449.2933650-2-xukuohai@huaweicloud.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | update 32-bit bounds when the lower 32-bit value is not wrapping | expand |
On 3/8/2023 6:04 AM, Xu Kuohai wrote: > The following XDP prog is accepted by verifier. > > 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) > 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) > 2: (bf) r1 = r2 > 3: (07) r1 += 1 > 4: (2d) if r1 > r3 goto pc+6 > 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) > 6: (b4) w0 = 0x7fffff10 > 7: (0c) w1 += w0 ; R1_w=scalar(umin=0x7fffff10,umax=0x8000000f,var_off=(0x0; 0xffffffff)) > 8: (b4) w0 = 0x80000000 > 9: (04) w0 += 1 > 10: (ae) if w0 < w1 goto pc-2 > 11: (b7) r0 = 0 > 12: (95) exit > > while the following 64-bit version is rejected. > > 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) > 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) > 2: (bf) r1 = r2 > 3: (07) r1 += 1 > 4: (2d) if r1 > r3 goto pc+8 > 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) > 6: (18) r0 = 0x7fffffffffffff10 > 8: (0f) r1 += r0 ; R1_w=scalar(umin=0x7fffffffffffff10,umax=0x800000000000000f) > 9: (18) r0 = 0x8000000000000000 > 11: (07) r0 += 1 > 12: (ad) if r0 < r1 goto pc-2 > 13: (b7) r0 = 0 > 14: (95) exit > > The verifier log says: > > [...] > > from 12 to 11: R0_w=-9223372036854775794 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 11: (07) r0 += 1 ; R0_w=-9223372036854775793 > 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 13: safe > > from 12 to 11: R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 11: (07) r0 += 1 ; R0_w=-9223372036854775792 > 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775792 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 13: safe > > [...] > > The loop crosses termination condition r0 == r1.umax, and does not stop. > > The reason is that when the verifier enumerates to r1.umin == r1.umax, the value > 0x800000000000000f of r1.umin is greater than U32_MAX, so __reg_combine_64_into_32 > sets the u32 range of r1 to [0, U32_MAX] instead of marking r1 as a constant, > making is_branch_taken() in check_cond_jmp_op() be skipped. > > To fix it, update 32-bit bounds when the lower 32-bit value is not wrapping, > even if the 64-bit value is beyond the range of [0, U32_MAX] or [S32_MIN, S32_MAX]. > > Signed-off-by: Xu Kuohai <xukuohai@huaweicloud.com> Oops, missing fixes tag, will resend > --- > kernel/bpf/verifier.c | 27 +++++++++++---------------- > 1 file changed, 11 insertions(+), 16 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index b2116ca78d9a..64c9ee3857ec 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -2013,26 +2013,21 @@ static void __reg_combine_32_into_64(struct bpf_reg_state *reg) > reg_bounds_sync(reg); > } > > -static bool __reg64_bound_s32(s64 a) > -{ > - return a >= S32_MIN && a <= S32_MAX; > -} > - > -static bool __reg64_bound_u32(u64 a) > -{ > - return a >= U32_MIN && a <= U32_MAX; > -} > - > static void __reg_combine_64_into_32(struct bpf_reg_state *reg) > { > + s64 smin = reg->smin_value; > + s64 smax = reg->smax_value; > + u64 umin = reg->umin_value; > + u64 umax = reg->umax_value; > + > __mark_reg32_unbounded(reg); > - if (__reg64_bound_s32(reg->smin_value) && __reg64_bound_s32(reg->smax_value)) { > - reg->s32_min_value = (s32)reg->smin_value; > - reg->s32_max_value = (s32)reg->smax_value; > + if ((u64)(smax - smin) <= (u64)U32_MAX && (s32)smin <= (s32)smax) { > + reg->s32_min_value = (s32)smin; > + reg->s32_max_value = (s32)smax; > } > - if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value)) { > - reg->u32_min_value = (u32)reg->umin_value; > - reg->u32_max_value = (u32)reg->umax_value; > + if (umax - umin <= U32_MAX && (u32)umin <= (u32)umax) { > + reg->u32_min_value = (u32)umin; > + reg->u32_max_value = (u32)umax; > } > reg_bounds_sync(reg); > }
On Tue, Mar 7, 2023 at 1:05 AM Xu Kuohai <xukuohai@huaweicloud.com> wrote: > > The following XDP prog is accepted by verifier. > > 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) > 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) > 2: (bf) r1 = r2 > 3: (07) r1 += 1 > 4: (2d) if r1 > r3 goto pc+6 > 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) > 6: (b4) w0 = 0x7fffff10 > 7: (0c) w1 += w0 ; R1_w=scalar(umin=0x7fffff10,umax=0x8000000f,var_off=(0x0; 0xffffffff)) > 8: (b4) w0 = 0x80000000 > 9: (04) w0 += 1 > 10: (ae) if w0 < w1 goto pc-2 > 11: (b7) r0 = 0 > 12: (95) exit > > while the following 64-bit version is rejected. > > 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) > 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) > 2: (bf) r1 = r2 > 3: (07) r1 += 1 > 4: (2d) if r1 > r3 goto pc+8 > 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) > 6: (18) r0 = 0x7fffffffffffff10 > 8: (0f) r1 += r0 ; R1_w=scalar(umin=0x7fffffffffffff10,umax=0x800000000000000f) > 9: (18) r0 = 0x8000000000000000 > 11: (07) r0 += 1 > 12: (ad) if r0 < r1 goto pc-2 > 13: (b7) r0 = 0 > 14: (95) exit These two programs are not equivalent. Not clear how apples to oranges comparison explains anything. > The verifier log says: > > [...] > > from 12 to 11: R0_w=-9223372036854775794 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 11: (07) r0 += 1 ; R0_w=-9223372036854775793 > 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 13: safe > > from 12 to 11: R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) First thing to debug is why umin is higher than umax. > 11: (07) r0 += 1 ; R0_w=-9223372036854775792 > 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775792 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > 13: safe > > [...] > > The loop crosses termination condition r0 == r1.umax, and does not stop. > > The reason is that when the verifier enumerates to r1.umin == r1.umax, the value > 0x800000000000000f of r1.umin is greater than U32_MAX, so __reg_combine_64_into_32 > sets the u32 range of r1 to [0, U32_MAX] instead of marking r1 as a constant, > making is_branch_taken() in check_cond_jmp_op() be skipped. And it's fine. The verifier is conservative. > > To fix it, update 32-bit bounds when the lower 32-bit value is not wrapping, > even if the 64-bit value is beyond the range of [0, U32_MAX] or [S32_MIN, S32_MAX]. That's not safe in general. > > Signed-off-by: Xu Kuohai <xukuohai@huaweicloud.com> > --- > kernel/bpf/verifier.c | 27 +++++++++++---------------- > 1 file changed, 11 insertions(+), 16 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index b2116ca78d9a..64c9ee3857ec 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -2013,26 +2013,21 @@ static void __reg_combine_32_into_64(struct bpf_reg_state *reg) > reg_bounds_sync(reg); > } > > -static bool __reg64_bound_s32(s64 a) > -{ > - return a >= S32_MIN && a <= S32_MAX; > -} > - > -static bool __reg64_bound_u32(u64 a) > -{ > - return a >= U32_MIN && a <= U32_MAX; > -} > - > static void __reg_combine_64_into_32(struct bpf_reg_state *reg) > { > + s64 smin = reg->smin_value; > + s64 smax = reg->smax_value; > + u64 umin = reg->umin_value; > + u64 umax = reg->umax_value; > + > __mark_reg32_unbounded(reg); > - if (__reg64_bound_s32(reg->smin_value) && __reg64_bound_s32(reg->smax_value)) { > - reg->s32_min_value = (s32)reg->smin_value; > - reg->s32_max_value = (s32)reg->smax_value; > + if ((u64)(smax - smin) <= (u64)U32_MAX && (s32)smin <= (s32)smax) { > + reg->s32_min_value = (s32)smin; > + reg->s32_max_value = (s32)smax; > } > - if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value)) { > - reg->u32_min_value = (u32)reg->umin_value; > - reg->u32_max_value = (u32)reg->umax_value; > + if (umax - umin <= U32_MAX && (u32)umin <= (u32)umax) { > + reg->u32_min_value = (u32)umin; > + reg->u32_max_value = (u32)umax; This looks like a workaround for umin > umax issue. Please debug that instead. > } > reg_bounds_sync(reg); > } > -- > 2.30.2 >
On 3/8/2023 1:22 AM, Alexei Starovoitov wrote: > On Tue, Mar 7, 2023 at 1:05 AM Xu Kuohai <xukuohai@huaweicloud.com> wrote: >> >> The following XDP prog is accepted by verifier. >> >> 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) >> 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) >> 2: (bf) r1 = r2 >> 3: (07) r1 += 1 >> 4: (2d) if r1 > r3 goto pc+6 >> 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) >> 6: (b4) w0 = 0x7fffff10 >> 7: (0c) w1 += w0 ; R1_w=scalar(umin=0x7fffff10,umax=0x8000000f,var_off=(0x0; 0xffffffff)) >> 8: (b4) w0 = 0x80000000 >> 9: (04) w0 += 1 >> 10: (ae) if w0 < w1 goto pc-2 >> 11: (b7) r0 = 0 >> 12: (95) exit >> >> while the following 64-bit version is rejected. >> >> 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) >> 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) >> 2: (bf) r1 = r2 >> 3: (07) r1 += 1 >> 4: (2d) if r1 > r3 goto pc+8 >> 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) >> 6: (18) r0 = 0x7fffffffffffff10 >> 8: (0f) r1 += r0 ; R1_w=scalar(umin=0x7fffffffffffff10,umax=0x800000000000000f) >> 9: (18) r0 = 0x8000000000000000 >> 11: (07) r0 += 1 >> 12: (ad) if r0 < r1 goto pc-2 >> 13: (b7) r0 = 0 >> 14: (95) exit > > These two programs are not equivalent. > Not clear how apples to oranges comparison explains anything. > Yes, they are not equivalent. I assumed the 32-bit prog being accepted implies it is unreasonable for the 64-bit prog to be rejected. Regardless of this assumption and the 32-bit prog, the above 64-bit prog is expected to be accepted, right? >> The verifier log says: >> >> [...] >> >> from 12 to 11: R0_w=-9223372036854775794 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) >> 11: (07) r0 += 1 ; R0_w=-9223372036854775793 >> 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) >> 13: safe >> >> from 12 to 11: R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) > > First thing to debug is why umin is higher than umax. > Well, it's because the loop does not stop, when r0 increases to -9223372036854775793, the following code in reg_set_min_max() sets umin_value to 9223372036854775824: case BPF_JGT: { if (is_jmp32) { [...] } else { u64 false_umax = opcode == BPF_JGT ? val : val - 1; u64 true_umin = opcode == BPF_JGT ? val + 1 : val; false_reg->umax_value = min(false_reg->umax_value, false_umax); true_reg->umin_value = max(true_reg->umin_value, true_umin); } break; } To avoid umin > umax, it could be changed it to: case BPF_JGT: { if (is_jmp32) { [...] } else { u64 false_umax = opcode == BPF_JGT ? val : val - 1; u64 true_umin = opcode == BPF_JGT ? val + 1 : val; false_reg->umax_value = min(false_reg->umax_value, false_umax); false_reg->umax_value = max(false_reg->umax_value, false_reg->umin_value); true_reg->umin_value = max(true_reg->umin_value, true_umin); true_reg->umin_value = min(true_reg->umax_value, true_reg->umin_value); } break; } The problem is that the loop still does not stop because tnum_is_const(src_reg->var_off) always returns false and is_branch_taken() is skipped: if (BPF_SRC(insn->code) == BPF_K) { [...] } else if (src_reg->type == SCALAR_VALUE && is_jmp32 && tnum_is_const(tnum_subreg(src_reg->var_off))) { [...] } else if (src_reg->type == SCALAR_VALUE && !is_jmp32 && tnum_is_const(src_reg->var_off)) { pred = is_branch_taken(dst_reg, // could not reach here src_reg->var_off.value, opcode, is_jmp32); } else if (reg_is_pkt_pointer_any(dst_reg) && reg_is_pkt_pointer_any(src_reg) && !is_jmp32) { [...] } Why tnum_is_const(src_reg->var_off) returns false is because the lower 32-bit is not constant since the lower 32-bit range is [U32_MIN, U32_MAX]. >> 11: (07) r0 += 1 ; R0_w=-9223372036854775792 >> 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775792 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) >> 13: safe >> >> [...] >> >> The loop crosses termination condition r0 == r1.umax, and does not stop. >> >> The reason is that when the verifier enumerates to r1.umin == r1.umax, the value >> 0x800000000000000f of r1.umin is greater than U32_MAX, so __reg_combine_64_into_32 >> sets the u32 range of r1 to [0, U32_MAX] instead of marking r1 as a constant, >> making is_branch_taken() in check_cond_jmp_op() be skipped. > > And it's fine. The verifier is conservative. > >> >> To fix it, update 32-bit bounds when the lower 32-bit value is not wrapping, >> even if the 64-bit value is beyond the range of [0, U32_MAX] or [S32_MIN, S32_MAX]. > > That's not safe in general. > >> >> Signed-off-by: Xu Kuohai <xukuohai@huaweicloud.com> >> --- >> kernel/bpf/verifier.c | 27 +++++++++++---------------- >> 1 file changed, 11 insertions(+), 16 deletions(-) >> >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index b2116ca78d9a..64c9ee3857ec 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -2013,26 +2013,21 @@ static void __reg_combine_32_into_64(struct bpf_reg_state *reg) >> reg_bounds_sync(reg); >> } >> >> -static bool __reg64_bound_s32(s64 a) >> -{ >> - return a >= S32_MIN && a <= S32_MAX; >> -} >> - >> -static bool __reg64_bound_u32(u64 a) >> -{ >> - return a >= U32_MIN && a <= U32_MAX; >> -} >> - >> static void __reg_combine_64_into_32(struct bpf_reg_state *reg) >> { >> + s64 smin = reg->smin_value; >> + s64 smax = reg->smax_value; >> + u64 umin = reg->umin_value; >> + u64 umax = reg->umax_value; >> + >> __mark_reg32_unbounded(reg); >> - if (__reg64_bound_s32(reg->smin_value) && __reg64_bound_s32(reg->smax_value)) { >> - reg->s32_min_value = (s32)reg->smin_value; >> - reg->s32_max_value = (s32)reg->smax_value; >> + if ((u64)(smax - smin) <= (u64)U32_MAX && (s32)smin <= (s32)smax) { >> + reg->s32_min_value = (s32)smin; >> + reg->s32_max_value = (s32)smax; >> } >> - if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value)) { >> - reg->u32_min_value = (u32)reg->umin_value; >> - reg->u32_max_value = (u32)reg->umax_value; >> + if (umax - umin <= U32_MAX && (u32)umin <= (u32)umax) { >> + reg->u32_min_value = (u32)umin; >> + reg->u32_max_value = (u32)umax; > > This looks like a workaround for umin > umax issue. > Please debug that instead. > "__reg64_bound_u32(umin) && __reg64_bound_u32(max)" is a special case of "umax - umin <= U32_MAX && (u32)umin <= (u32)umax " when umax <= U32_MAX. If it's only safe to set lower 32-bit range to [U32_MIN, U32_MAX] when umax > U32_MAX, could we infer the 64-bit value is a constant from umin == umax? >> } >> reg_bounds_sync(reg); >> } >> -- >> 2.30.2 >> > .
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b2116ca78d9a..64c9ee3857ec 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2013,26 +2013,21 @@ static void __reg_combine_32_into_64(struct bpf_reg_state *reg) reg_bounds_sync(reg); } -static bool __reg64_bound_s32(s64 a) -{ - return a >= S32_MIN && a <= S32_MAX; -} - -static bool __reg64_bound_u32(u64 a) -{ - return a >= U32_MIN && a <= U32_MAX; -} - static void __reg_combine_64_into_32(struct bpf_reg_state *reg) { + s64 smin = reg->smin_value; + s64 smax = reg->smax_value; + u64 umin = reg->umin_value; + u64 umax = reg->umax_value; + __mark_reg32_unbounded(reg); - if (__reg64_bound_s32(reg->smin_value) && __reg64_bound_s32(reg->smax_value)) { - reg->s32_min_value = (s32)reg->smin_value; - reg->s32_max_value = (s32)reg->smax_value; + if ((u64)(smax - smin) <= (u64)U32_MAX && (s32)smin <= (s32)smax) { + reg->s32_min_value = (s32)smin; + reg->s32_max_value = (s32)smax; } - if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value)) { - reg->u32_min_value = (u32)reg->umin_value; - reg->u32_max_value = (u32)reg->umax_value; + if (umax - umin <= U32_MAX && (u32)umin <= (u32)umax) { + reg->u32_min_value = (u32)umin; + reg->u32_max_value = (u32)umax; } reg_bounds_sync(reg); }
The following XDP prog is accepted by verifier. 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) 2: (bf) r1 = r2 3: (07) r1 += 1 4: (2d) if r1 > r3 goto pc+6 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) 6: (b4) w0 = 0x7fffff10 7: (0c) w1 += w0 ; R1_w=scalar(umin=0x7fffff10,umax=0x8000000f,var_off=(0x0; 0xffffffff)) 8: (b4) w0 = 0x80000000 9: (04) w0 += 1 10: (ae) if w0 < w1 goto pc-2 11: (b7) r0 = 0 12: (95) exit while the following 64-bit version is rejected. 0: (61) r2 = *(u32 *)(r1 +0) ; R2_w=pkt(off=0,r=0,imm=0) 1: (61) r3 = *(u32 *)(r1 +4) ; R3_w=pkt_end(off=0,imm=0) 2: (bf) r1 = r2 3: (07) r1 += 1 4: (2d) if r1 > r3 goto pc+8 5: (71) r1 = *(u8 *)(r2 +0) ; R1_w=scalar(umax=255,var_off=(0x0; 0xff)) 6: (18) r0 = 0x7fffffffffffff10 8: (0f) r1 += r0 ; R1_w=scalar(umin=0x7fffffffffffff10,umax=0x800000000000000f) 9: (18) r0 = 0x8000000000000000 11: (07) r0 += 1 12: (ad) if r0 < r1 goto pc-2 13: (b7) r0 = 0 14: (95) exit The verifier log says: [...] from 12 to 11: R0_w=-9223372036854775794 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) 11: (07) r0 += 1 ; R0_w=-9223372036854775793 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775823,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) 13: safe from 12 to 11: R0_w=-9223372036854775793 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) 11: (07) r0 += 1 ; R0_w=-9223372036854775792 12: (ad) if r0 < r1 goto pc-2 ; R0_w=-9223372036854775792 R1=scalar(umin=9223372036854775824,umax=9223372036854775823,var_off=(0x8000000000000000; 0xffffffff)) 13: safe [...] The loop crosses termination condition r0 == r1.umax, and does not stop. The reason is that when the verifier enumerates to r1.umin == r1.umax, the value 0x800000000000000f of r1.umin is greater than U32_MAX, so __reg_combine_64_into_32 sets the u32 range of r1 to [0, U32_MAX] instead of marking r1 as a constant, making is_branch_taken() in check_cond_jmp_op() be skipped. To fix it, update 32-bit bounds when the lower 32-bit value is not wrapping, even if the 64-bit value is beyond the range of [0, U32_MAX] or [S32_MIN, S32_MAX]. Signed-off-by: Xu Kuohai <xukuohai@huaweicloud.com> --- kernel/bpf/verifier.c | 27 +++++++++++---------------- 1 file changed, 11 insertions(+), 16 deletions(-)