On Sun, May 3, 2020 at 11:28 PM Yonghong Song <yhs@xxxxxx> wrote:
>
> This specifically to handle the case like below:
> // ptr below is a socket ptr identified by PTR_TO_BTF_ID
> u64 param[2] = { ptr, val };
> bpf_seq_printf(seq, fmt, sizeof(fmt), param, sizeof(param));
>
> In this case, the 16 bytes stack for "param" contains:
> 8 bytes for ptr with spilled PTR_TO_BTF_ID
> 8 bytes for val as STACK_MISC
>
> The current verifier will complain the ptr should not be visible
> to the helper.
> ...
> 16: (7b) *(u64 *)(r10 -64) = r2
> 18: (7b) *(u64 *)(r10 -56) = r1
> 19: (bf) r4 = r10
> ;
> 20: (07) r4 += -64
> ; BPF_SEQ_PRINTF(seq, fmt1, (long)s, s->sk_protocol);
> 21: (bf) r1 = r6
> 22: (18) r2 = 0xffffa8d00018605a
> 24: (b4) w3 = 10
> 25: (b4) w5 = 16
> 26: (85) call bpf_seq_printf#125
> R0=inv(id=0) R1_w=ptr_seq_file(id=0,off=0,imm=0)
> R2_w=map_value(id=0,off=90,ks=4,vs=144,imm=0) R3_w=inv10
> R4_w=fp-64 R5_w=inv16 R6=ptr_seq_file(id=0,off=0,imm=0)
> R7=ptr_netlink_sock(id=0,off=0,imm=0) R10=fp0 fp-56_w=mmmmmmmm
> fp-64_w=ptr_
> last_idx 26 first_idx 13
> regs=8 stack=0 before 25: (b4) w5 = 16
> regs=8 stack=0 before 24: (b4) w3 = 10
> invalid indirect read from stack off -64+0 size 16
>
> Let us permit this if the program is a tracing/iter program.
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
LGTM, but I wonder why enabling this only for iterator programs?
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> kernel/bpf/verifier.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 36b2a38a06fe..4884b6fd7bad 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3494,6 +3494,14 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
> *stype = STACK_MISC;
> goto mark;
> }
> +
> + /* pointer value can be visible to tracing/iter program */
> + if (env->prog->type == BPF_PROG_TYPE_TRACING &&
> + env->prog->expected_attach_type == BPF_TRACE_ITER &&
What's the problem allowing this for all program types?
> + state->stack[spi].slot_type[0] == STACK_SPILL &&
> + state->stack[spi].spilled_ptr.type == PTR_TO_BTF_ID)
> + goto mark;
> +
> if (state->stack[spi].slot_type[0] == STACK_SPILL &&
> state->stack[spi].spilled_ptr.type == SCALAR_VALUE) {
> __mark_reg_unknown(env, &state->stack[spi].spilled_ptr);
> --
> 2.24.1
>
