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bpf: allow map helpers access to map values directly

PATCH Applied Paul Chaignon via iovisor-dev 1 participant 1 message Apr 24, 2018

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Networking Network drivers BPF BPF core
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Paul Chaignon via iovisor-dev

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PATCH v5 1/2 bpf: allow map helpers access to map values directly

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 <[email protected]>
---
 kernel/bpf/verifier.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)
kernel/bpf/verifier.c +7 -17
index 5dd1dcb..eb1a596 100644
@@ -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 ||

@@ -1966,14 +1966,9 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 			verbose(env, "invalid map_ptr to access map->key\n");
 			return -EACCES;
 		}
-		if (type_is_pkt_pointer(type))
-			err = check_packet_access(env, regno, reg->off,
-						  meta->map_ptr->key_size,
-						  false);
-		else
-			err = check_stack_boundary(env, regno,
-						   meta->map_ptr->key_size,
-						   false, NULL);
+		err = check_helper_mem_access(env, regno,
+					      meta->map_ptr->key_size, false,
+					      NULL);
 	} else if (arg_type == ARG_PTR_TO_MAP_VALUE) {
 		/* bpf_map_xxx(..., map_ptr, ..., value) call:
 		 * check [value, value + map->value_size) validity

@@ -1983,14 +1978,9 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 			verbose(env, "invalid map_ptr to access map->value\n");
 			return -EACCES;
 		}
-		if (type_is_pkt_pointer(type))
-			err = check_packet_access(env, regno, reg->off,
-						  meta->map_ptr->value_size,
-						  false);
-		else
-			err = check_stack_boundary(env, regno,
-						   meta->map_ptr->value_size,
-						   false, NULL);
+		err = check_helper_mem_access(env, regno,
+					      meta->map_ptr->value_size, false,
+					      NULL);
 	} else if (arg_type_is_mem_size(arg_type)) {
 		bool zero_size_allowed = (arg_type == ARG_CONST_SIZE_OR_ZERO);
Signature · 1 line
2.7.4