[PATCH bpf-next v3 06/11] bpf: Fix compare error in function retval_range_within

[Andrii Nakryiko]

On Thu, Apr 11, 2024 at 5:24 AM Xu Kuohai <xukuohai at huaweicloud.com> wrote:
>
> From: Xu Kuohai <xukuohai at huawei.com>
>
> After checking lsm hook return range in verifier, the test case
> "test_progs -t test_lsm" failed, and the failure log says:
>
> libbpf: prog 'test_int_hook': BPF program load failed: Invalid argument
> libbpf: prog 'test_int_hook': -- BEGIN PROG LOAD LOG --
> 0: R1=ctx() R10=fp0
> ; int BPF_PROG(test_int_hook, struct vm_area_struct *vma, @ lsm.c:89
> 0: (79) r0 = *(u64 *)(r1 +24)         ; R0_w=scalar(smin=smin32=-4095,smax=smax32=0) R1=ctx()
>
> [...]
>
> 24: (b4) w0 = -1                      ; R0_w=0xffffffff
> ; int BPF_PROG(test_int_hook, struct vm_area_struct *vma, @ lsm.c:89
> 25: (95) exit
> At program exit the register R0 has smin=4294967295 smax=4294967295 should have been in [-4095, 0]
>
> It can be seen that instruction "w0 = -1" zero extended -1 to 64-bit
> register r0, setting both smin and smax values of r0 to 4294967295.
> This resulted in a false reject when r0 was checked with range [-4095, 0].
>
> Given bpf_retval_range is a 32-bit range, this patch fixes it by
> changing the compare between r0 and return range from 64-bit
> operation to 32-bit operation.
>
> Fixes: 8fa4ecd49b81 ("bpf: enforce exact retval range on subprog/callback exit")
> Signed-off-by: Xu Kuohai <xukuohai at huawei.com>
> ---
>  kernel/bpf/verifier.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 05c7c5f2bec0..5393d576c76f 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -9879,7 +9879,7 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
>
>  static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
>  {
> -       return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
> +       return range.minval <= reg->s32_min_value && reg->s32_max_value <= range.maxval;

are all BPF programs treated as if they return int instead of long? If
not, we probably should have a bool flag in bpf_retval_range whether
comparison should be 32-bit or 64-bit?

>  }
>
>  static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
> --
> 2.30.2
>