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authorYonghong Song <yhs@fb.com>2020-12-10 04:33:49 +0300
committerDaniel Borkmann <daniel@iogearbox.net>2020-12-14 23:50:10 +0300
commitcd17d38f8b28f808c368121041c0a4fa91757e0d (patch)
tree2680d4ddec820fb6db0f787ad2308093ca1a0450 /kernel/bpf
parenta4d2a7ad86834092b327082004ead755d2603376 (diff)
downloadlinux-cd17d38f8b28f808c368121041c0a4fa91757e0d.tar.xz
bpf: Permits pointers on stack for helper calls
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
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/verifier.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 93def76cf32b..9159c9822ede 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3769,7 +3769,8 @@ 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;