On 08/16, Andrii Nakryiko wrote:
On Mon, Aug 16, 2021 at 2:43 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx>
wrote:
>
> On 8/16/21 6:48 PM, Stanislav Fomichev wrote:
> > Use kvmalloc/kvfree for temporary value when looking up a map.
> > kmalloc might not be sufficient for percpu maps where the value is
big.
> >
> > Can be reproduced with netcnt test on qemu with "-smp 255".
> >
> > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > ---
> > kernel/bpf/syscall.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 9a2068e39d23..ae0b1c1c8ece 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -1076,7 +1076,7 @@ static int map_lookup_elem(union bpf_attr *attr)
> > value_size = bpf_map_value_size(map);
> >
> > err = -ENOMEM;
> > - value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
> > + value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
> > if (!value)
> > goto free_key;
>
> What about other cases like map_update_elem(), shouldn't they be adapted
> similarly?
And in the same vein (with keys potentially being big as well), should
we switch __bpf_copy_key() to use vmemdup_user() instead of
memdup_user()?
Those are good questions :-)
I'm assuming that whatever is doing kmalloc on top of
bpf_map_value_size() should definitely use kvmalloc since
bpf_map_value_size() can blow up the value size. (will resend)
For __bpf_copy_key I'm less sure, but it might be a good idea as well.
Let me try to look at bit more into it, but feels like there shouldn't
be any downsides?
