On 04/22/2018 11:52 PM, Paul Chaignon wrote:
> 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.chaig...@orange.com>
> ---
> kernel/bpf/verifier.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 5dd1dcb902bf..70e00beade03 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1914,7 +1914,7 @@ static int check_func_arg(struct bpf_verifier_env *env,
> u32 regno,
> if (arg_type == ARG_PTR_TO_MAP_KEY ||
> arg_type == ARG_PTR_TO_MAP_VALUE) {
> expected_type = PTR_TO_STACK;
> - if (!type_is_pkt_pointer(type) &&
> + if (!type_is_pkt_pointer(type) && type != PTR_TO_MAP_VALUE &&
> type != expected_type)
> goto err_type;
> } else if (arg_type == ARG_CONST_SIZE ||
> @@ -1970,6 +1970,9 @@ static int check_func_arg(struct bpf_verifier_env *env,
> u32 regno,
> err = check_packet_access(env, regno, reg->off,
> meta->map_ptr->key_size,
> false);
> + else if (type == PTR_TO_MAP_VALUE)
> + err = check_map_access(env, regno, reg->off,
> + meta->map_ptr->key_size, false);
> else
> err = check_stack_boundary(env, regno,
> meta->map_ptr->key_size,
We should reuse check_helper_mem_access() here which covers all three cases
from above already and simplifies the code a bit.
> @@ -1987,6 +1990,10 @@ static int check_func_arg(struct bpf_verifier_env
> *env, u32 regno,
> err = check_packet_access(env, regno, reg->off,
> meta->map_ptr->value_size,
> false);
> + else if (type == PTR_TO_MAP_VALUE)
> + err = check_map_access(env, regno, reg->off,
> + meta->map_ptr->value_size,
> + false);
> else
> err = check_stack_boundary(env, regno,
> meta->map_ptr->value_size,
>
Ditto.
Thanks,
Daniel
