On 04/23/2018 11:18 PM +0200, Daniel Borkmann wrote:
> 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.
Thanks for the review.
I've sent a refactored patchset that uses check_helper_mem_access().
>
> > @@ -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
