Hi Youlin,
On Thu, Jul 28, 2022 at 9:44 PM Youlin Li <liulin063@xxxxxxxxx> wrote:
>
> 32bit bounds and 64bit bounds are updated separately in
> adjust_scalar_min_max_vals() currently, let them learn from each other to
> get more tight bounds tracking. Similar operation can be found in
> reg_set_min_max().
>
> 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
>
> Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
This change looks to me like an improvement, rather than a bug fix. We
probably don't need this tag.
> Signed-off-by: Youlin Li <liulin063@xxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 0efbac0fd126..888aa50fbdc0 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -8934,10 +8934,13 @@ 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);
> + __reg_combine_32_into_64(dst_reg);
This __reg_combine_32_into_64 can be replaced with simply
reg_bounds_sync, because the above zext_32_to_64 has already
propagated 32 to 64. Using reg_bounds_sync would be more efficient.
It turns out we can now fold reg_bounds_sync into zext_32_to_64. Can
you do that and resend? IMO that will make the code slightly cleaner.
> + } else {
> + __reg_combine_64_into_32(dst_reg);
> + }
> return 0;
> }
>
> --
> 2.25.1
>
