From: Yonghong Song yhs@fb.com
[ Upstream commit cd17d38f8b28f808c368121041c0a4fa91757e0d ]
Currently, when checking stack memory accessed by helper calls, for spills, only PTR_TO_BTF_ID and SCALAR_VALUE are allowed.
Song discovered an issue where the below bpf program int dump_task(struct bpf_iter__task *ctx) { struct seq_file *seq = ctx->meta->seq; static char[] info = "abc"; BPF_SEQ_PRINTF(seq, "%s\n", info); return 0; } may cause a verifier failure.
The verifier output looks like: ; struct seq_file *seq = ctx->meta->seq; 1: (79) r1 = *(u64 *)(r1 +0) ; BPF_SEQ_PRINTF(seq, "%s\n", info); 2: (18) r2 = 0xffff9054400f6000 4: (7b) *(u64 *)(r10 -8) = r2 5: (bf) r4 = r10 ; 6: (07) r4 += -8 ; BPF_SEQ_PRINTF(seq, "%s\n", info); 7: (18) r2 = 0xffff9054400fe000 9: (b4) w3 = 4 10: (b4) w5 = 8 11: (85) call bpf_seq_printf#126 R1_w=ptr_seq_file(id=0,off=0,imm=0) R2_w=map_value(id=0,off=0,ks=4,vs=4,imm=0) R3_w=inv4 R4_w=fp-8 R5_w=inv8 R10=fp0 fp-8_w=map_value last_idx 11 first_idx 0 regs=8 stack=0 before 10: (b4) w5 = 8 regs=8 stack=0 before 9: (b4) w3 = 4 invalid indirect read from stack off -8+0 size 8
Basically, the verifier complains the map_value pointer at "fp-8" location. To fix the issue, if env->allow_ptr_leaks is true, let us also permit pointers on the stack to be accessible by the helper.
Reported-by: Song Liu songliubraving@fb.com Suggested-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Yonghong Song yhs@fb.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Song Liu songliubraving@fb.com Link: https://lore.kernel.org/bpf/20201210013349.943719-1-yhs@fb.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 3370f0d476e9..2e09e691a6be 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3759,7 +3759,8 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, goto mark;
if (state->stack[spi].slot_type[0] == STACK_SPILL && - state->stack[spi].spilled_ptr.type == SCALAR_VALUE) { + (state->stack[spi].spilled_ptr.type == SCALAR_VALUE || + env->allow_ptr_leaks)) { __mark_reg_unknown(env, &state->stack[spi].spilled_ptr); for (j = 0; j < BPF_REG_SIZE; j++) state->stack[spi].slot_type[j] = STACK_MISC;