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

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

[Andrii Nakryiko]

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 <andriin@fb.com>
---
 kernel/bpf/ringbuf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index 180414bb0d3e..dcc8e8b9df10 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -132,7 +132,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
 {
 	struct bpf_ringbuf *rb;
 
-	if (!data_sz || !PAGE_ALIGNED(data_sz))
+	if (!is_power_of_2(data_sz) || !PAGE_ALIGNED(data_sz))
 		return ERR_PTR(-EINVAL);
 
 #ifdef CONFIG_64BIT
@@ -166,7 +166,8 @@ 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))
 		return ERR_PTR(-EINVAL);
 
 	rb_map = kzalloc(sizeof(*rb_map), GFP_USER);
-- 
2.24.1

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

[Yonghong Song]

On 6/29/20 3:17 PM, 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 <andriin@fb.com>

Acked-by: Yonghong Song <yhs@fb.com>

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

[Alexei Starovoitov]

On Mon, Jun 29, 2020 at 3:19 PM Andrii Nakryiko <andriin@fb.com> 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 <andriin@fb.com>
> ---
>  kernel/bpf/ringbuf.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
> index 180414bb0d3e..dcc8e8b9df10 100644
> --- a/kernel/bpf/ringbuf.c
> +++ b/kernel/bpf/ringbuf.c
> @@ -132,7 +132,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
>  {
>         struct bpf_ringbuf *rb;
>
> -       if (!data_sz || !PAGE_ALIGNED(data_sz))
> +       if (!is_power_of_2(data_sz) || !PAGE_ALIGNED(data_sz))
>                 return ERR_PTR(-EINVAL);

What's the point checking the same value in two different places?
The check below did that already.

>  #ifdef CONFIG_64BIT
> @@ -166,7 +166,8 @@ 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))
>                 return ERR_PTR(-EINVAL);
>
>         rb_map = kzalloc(sizeof(*rb_map), GFP_USER);
> --
> 2.24.1
>

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

[Andrii Nakryiko]

On Mon, Jun 29, 2020 at 9:47 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Jun 29, 2020 at 3:19 PM Andrii Nakryiko <andriin@fb.com> 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 <andriin@fb.com>
> > ---
> >  kernel/bpf/ringbuf.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
> > index 180414bb0d3e..dcc8e8b9df10 100644
> > --- a/kernel/bpf/ringbuf.c
> > +++ b/kernel/bpf/ringbuf.c
> > @@ -132,7 +132,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
> >  {
> >         struct bpf_ringbuf *rb;
> >
> > -       if (!data_sz || !PAGE_ALIGNED(data_sz))
> > +       if (!is_power_of_2(data_sz) || !PAGE_ALIGNED(data_sz))
> >                 return ERR_PTR(-EINVAL);
>
> What's the point checking the same value in two different places?
> The check below did that already.

I was initially treating bpf_ringbuf_alloc() as a sort of internal API
that some other code (outside of BPF map) might want to use. But I'll
drop for now, it can always be added later.

>
> >  #ifdef CONFIG_64BIT
> > @@ -166,7 +166,8 @@ 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))
> >                 return ERR_PTR(-EINVAL);
> >
> >         rb_map = kzalloc(sizeof(*rb_map), GFP_USER);
> > --
> > 2.24.1
> >