From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Chaignon via iovisor-dev Subject: Re: [PATCH bpf-next v4 1/2] bpf: allow map helpers access to map values directly Date: Tue, 24 Apr 2018 15:50:15 +0200 Message-ID: <20180424135013.GA6643@Nover> References: <3c8b73a6ea66eb01419da4ff0c611f72c7905a5a.1524407665.git.paul.chaignon@orange.com> Reply-To: Paul Chaignon Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: iovisor-dev-9jONkmmOlFHEE9lA1F8Ukti2O/JbrIOy@public.gmane.org To: Daniel Borkmann , Alexei Starovoitov , netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iovisor-dev-bounces-9jONkmmOlFHEE9lA1F8Ukti2O/JbrIOy@public.gmane.org Errors-To: iovisor-dev-bounces-9jONkmmOlFHEE9lA1F8Ukti2O/JbrIOy@public.gmane.org List-Id: netdev.vger.kernel.org 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 > > --- > > 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