Re: [PATCH bpf-next v3 1/2] bpf: permits pointers on stack for helper calls

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





On 12/14/20 1:26 PM, Daniel Borkmann wrote:
On 12/11/20 4:41 AM, Yonghong Song wrote:
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.

Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Reported-by: Song Liu <songliubraving@xxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
  kernel/bpf/verifier.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 93def76cf32b..eebb2d3e16bf 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3769,7 +3769,9 @@ 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 ||
+             (state->stack[spi].spilled_ptr.type != NOT_INIT &&

Thinking more on this, your v2 was actually correct since in such case stype would have been STACK_MISC or STACK_ZERO and we would have jumped to goto mark here instead, so the above is not reachable under NOT_INIT. Anyway, I took the
v2 in, thanks!

Thanks! I missed this (NOT_INIT is associated with STACK_MISC/STACK_ZERO spill type) too.


+              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;






[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux