kernel/bpf/verifier.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
In adjust_scalar_min_max_vals(), let 32bit bounds learn from 64bit bounds
to get more tight bounds tracking. Similar operation can be found in
reg_set_min_max().
Also, we can now fold reg_bounds_sync() into zext_32_to_64().
Before:
func#0 @0
0: R1=ctx(off=0,imm=0) R10=fp0
0: (b7) r0 = 0 ; R0_w=0
1: (b7) r1 = 0 ; R1_w=0
2: (87) r1 = -r1 ; R1_w=scalar()
3: (87) r1 = -r1 ; R1_w=scalar()
4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0)
5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0xffffffff)) <--- [*]
6: (95) exit
It can be seen that even if the 64bit bounds is clear here, the 32bit
bounds is still in the state of 'UNKNOWN'.
After:
func#0 @0
0: R1=ctx(off=0,imm=0) R10=fp0
0: (b7) r0 = 0 ; R0_w=0
1: (b7) r1 = 0 ; R1_w=0
2: (87) r1 = -r1 ; R1_w=scalar()
3: (87) r1 = -r1 ; R1_w=scalar()
4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0)
5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0x3)) <--- [*]
6: (95) exit
Signed-off-by: Youlin Li <liulin063@gmail.com>
---
kernel/bpf/verifier.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0efbac0fd126..1f5c6e3634d6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4383,6 +4383,7 @@ static void zext_32_to_64(struct bpf_reg_state *reg)
{
reg->var_off = tnum_subreg(reg->var_off);
__reg_assign_32_into_64(reg);
+ reg_bounds_sync(reg);
}
/* truncate register to smaller size (in bytes)
@@ -8934,10 +8935,12 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
break;
}
- /* ALU32 ops are zero extended into 64bit register */
- if (alu32)
+ if (alu32) {
+ /* ALU32 ops are zero extended into 64bit register */
zext_32_to_64(dst_reg);
- reg_bounds_sync(dst_reg);
+ } else {
+ __reg_combine_64_into_32(dst_reg);
+ }
return 0;
}
@@ -9126,7 +9129,6 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
insn->dst_reg);
}
zext_32_to_64(dst_reg);
- reg_bounds_sync(dst_reg);
}
} else {
/* case: R = imm
--
2.25.1On Fri, Jul 29, 2022 at 3:43 PM Youlin Li <liulin063@gmail.com> wrote: > > In adjust_scalar_min_max_vals(), let 32bit bounds learn from 64bit bounds > to get more tight bounds tracking. Similar operation can be found in > reg_set_min_max(). > > Also, we can now fold reg_bounds_sync() into zext_32_to_64(). > > Before: > > func#0 @0 > 0: R1=ctx(off=0,imm=0) R10=fp0 > 0: (b7) r0 = 0 ; R0_w=0 > 1: (b7) r1 = 0 ; R1_w=0 > 2: (87) r1 = -r1 ; R1_w=scalar() > 3: (87) r1 = -r1 ; R1_w=scalar() > 4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0) > 5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0xffffffff)) <--- [*] > 6: (95) exit > > It can be seen that even if the 64bit bounds is clear here, the 32bit > bounds is still in the state of 'UNKNOWN'. > > After: > > func#0 @0 > 0: R1=ctx(off=0,imm=0) R10=fp0 > 0: (b7) r0 = 0 ; R0_w=0 > 1: (b7) r1 = 0 ; R1_w=0 > 2: (87) r1 = -r1 ; R1_w=scalar() > 3: (87) r1 = -r1 ; R1_w=scalar() > 4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0) > 5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0x3)) <--- [*] > 6: (95) exit > > Signed-off-by: Youlin Li <liulin063@gmail.com> Looks good to me. Thanks Youlin. Acked-by: Hao Luo <haoluo@google.com> Hao
On 7/30/22 12:48 AM, Hao Luo wrote: > On Fri, Jul 29, 2022 at 3:43 PM Youlin Li <liulin063@gmail.com> wrote: >> >> In adjust_scalar_min_max_vals(), let 32bit bounds learn from 64bit bounds >> to get more tight bounds tracking. Similar operation can be found in >> reg_set_min_max(). >> >> Also, we can now fold reg_bounds_sync() into zext_32_to_64(). >> >> Before: >> >> func#0 @0 >> 0: R1=ctx(off=0,imm=0) R10=fp0 >> 0: (b7) r0 = 0 ; R0_w=0 >> 1: (b7) r1 = 0 ; R1_w=0 >> 2: (87) r1 = -r1 ; R1_w=scalar() >> 3: (87) r1 = -r1 ; R1_w=scalar() >> 4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0) >> 5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0xffffffff)) <--- [*] >> 6: (95) exit >> >> It can be seen that even if the 64bit bounds is clear here, the 32bit >> bounds is still in the state of 'UNKNOWN'. >> >> After: >> >> func#0 @0 >> 0: R1=ctx(off=0,imm=0) R10=fp0 >> 0: (b7) r0 = 0 ; R0_w=0 >> 1: (b7) r1 = 0 ; R1_w=0 >> 2: (87) r1 = -r1 ; R1_w=scalar() >> 3: (87) r1 = -r1 ; R1_w=scalar() >> 4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0) >> 5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0x3)) <--- [*] >> 6: (95) exit >> >> Signed-off-by: Youlin Li <liulin063@gmail.com> > > Looks good to me. Thanks Youlin. > > Acked-by: Hao Luo <haoluo@google.com> Thanks Youlin! Looks like the patch breaks CI [0] e.g.: #142/p bounds check after truncation of non-boundary-crossing range FAIL Failed to load prog 'Permission denied'! invalid access to map value, value_size=8 off=16777215 size=1 R0 max value is outside of the allowed memory range verification time 296 usec stack depth 8 processed 15 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0 Please take a look. Also it would be great to add a test_verifier selftest to assert above case from commit log against future changes. Thanks, Daniel [0] https://github.com/kernel-patches/bpf/runs/7696324041?check_suite_focus=true
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