Re: [PATCH v2 bpf] bpf: enforce BPF ringbuf size to be the power of 2

[Daniel Borkmann]

On 6/30/20 8:15 AM, Andrii Nakryiko wrote:

BPF ringbuf assumes the size to be a multiple of page size and the power of
2 value. The latter is important to avoid division while calculating position
inside the ring buffer and using (N-1) mask instead. This patch fixes omission
to enforce power-of-2 size rule.

Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for 
it")
Signed-off-by: Andrii Nakryiko <andr...@fb.com>

Lgtm, applied, thanks!

[...]

@@ -166,9 +157,16 @@ static struct bpf_map *ringbuf_map_alloc(union bpf_attr 
*attr)
                return ERR_PTR(-EINVAL);

if (attr->key_size || attr->value_size ||

-           attr->max_entries == 0 || !PAGE_ALIGNED(attr->max_entries))
+           !is_power_of_2(attr->max_entries) ||
+           !PAGE_ALIGNED(attr->max_entries))

Technically !IS_ALIGNED(attr->max_entries, PAGE_SIZE) might have been a bit 
cleaner
since PAGE_ALIGNED() is only intended for pointers, though, not wrong here given
max_entries is u32.

Thanks,
Daniel