Re: [PATCH v2 bpf-next 1/7] bpf: implement BPF ring buffer and verifier support for it
From: Alexei Starovoitov <hidden>
Date: 2020-05-22 01:07:26
Also in:
bpf
On Sun, May 17, 2020 at 12:57:21PM -0700, Andrii Nakryiko wrote:
- if (off < 0 || size < 0 || (size == 0 && !zero_size_allowed) ||
- off + size > map->value_size) {
- verbose(env, "invalid access to map value, value_size=%d off=%d size=%d\n",
- map->value_size, off, size);
- return -EACCES;
- }
- return 0;
+ if (off >= 0 && size_ok && off + size <= mem_size)
+ return 0;
+
+ verbose(env, "invalid access to memory, mem_size=%u off=%d size=%d\n",
+ mem_size, off, size);
+ return -EACCES;iirc invalid access to map value is one of most common verifier errors that people see when they're use unbounded access. Generalizing it to memory is technically correct, but it makes the message harder to decipher. What is 'mem_size' ? Without context it is difficult to guess that it's actually size of map value element. Could you make this error message more human friendly depending on type of pointer?
quoted hunk ↗ jump to hunk
if (err) { - verbose(env, "R%d min value is outside of the array range\n", + verbose(env, "R%d min value is outside of the memory region\n", regno); return err; }@@ -2518,18 +2527,38 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno, * If reg->umax_value + off could overflow, treat that as unbounded too. */ if (reg->umax_value >= BPF_MAX_VAR_OFF) { - verbose(env, "R%d unbounded memory access, make sure to bounds check any array access into a map\n", + verbose(env, "R%d unbounded memory access, make sure to bounds check any memory region access\n", regno); return -EACCES; } - err = __check_map_access(env, regno, reg->umax_value + off, size, + err = __check_mem_access(env, reg->umax_value + off, size, mem_size, zero_size_allowed); - if (err) - verbose(env, "R%d max value is outside of the array range\n", + if (err) { + verbose(env, "R%d max value is outside of the memory region\n", regno);
I'm not that worried about above three generalizations of errors, but if you can make it friendly by describing type of memory region I think it will be a plus.