Re: [PATCH bpf-next] bpf: use kvmalloc in map_lookup_elem

On Mon, Aug 16, 2021 at 2:43 PM Daniel Borkmann [off-list ref] wrote:

On 8/16/21 6:48 PM, Stanislav Fomichev wrote:

quoted

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 <redacted>
---
  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()?

Thanks,
Daniel