bpf: allow map helpers access to map values directly

Browse source

Helpers that expect ARG_PTR_TO_MAP_KEY and ARG_PTR_TO_MAP_VALUE can only
access stack and packet memory.  Allow these helpers to directly access
map values by passing registers of type PTR_TO_MAP_VALUE.

This change removes the need for an extra copy to the stack when using a
map value to perform a second map lookup, as in the following:

struct bpf_map_def SEC("maps") infobyreq = {
    .type = BPF_MAP_TYPE_HASHMAP,
    .key_size = sizeof(struct request *),
    .value_size = sizeof(struct info_t),
    .max_entries = 1024,
};
struct bpf_map_def SEC("maps") counts = {
    .type = BPF_MAP_TYPE_HASHMAP,
    .key_size = sizeof(struct info_t),
    .value_size = sizeof(u64),
    .max_entries = 1024,
};
SEC("kprobe/blk_account_io_start")
int bpf_blk_account_io_start(struct pt_regs *ctx)
{
    struct info_t *info = bpf_map_lookup_elem(&infobyreq, &ctx->di);
    u64 *count = bpf_map_lookup_elem(&counts, info);
    (*count)++;
}

Signed-off-by: Paul Chaignon <paul.chaignon@orange.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

...

This commit is contained in:

Paul Chaignon 2018-04-24 15:07:54 +02:00 • committed by Daniel Borkmann

parent 0e25d14e5f

commit d71962f3e6

1 changed files with 7 additions and 17 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

24

kernel/bpf/verifier.c

View file