On 5/6/20 10:38 AM, Andrii Nakryiko wrote:
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?
Just want to conservative here since we may leak kernel pointers. But probably we are fine since the spill type is PTR_TO_BTF_ID which means tracing/raw_tp related bpf programs which should be okay. Will remove the above additional check, which I added in v2 of the patch.
+ 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
