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Date: Mon, 28 May 2018 02:43:38 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: ast@...nel.org
Cc: netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf-next 05/11] bpf: avoid retpoline for lookup/update/delete calls on maps
While some of the BPF map lookup helpers provide a ->map_gen_lookup()
callback for inlining the map lookup altogether it is not available
for every map, so the remaining ones have to call bpf_map_lookup_elem()
helper which does a dispatch to map->ops->map_lookup_elem(). In
times of retpolines, this will control and trap speculative execution
rather than letting it do its work for the indirect call and will
therefore cause a slowdown. Likewise, bpf_map_update_elem() and
bpf_map_delete_elem() do not have an inlined version and need to call
into their map->ops->map_update_elem() resp. map->ops->map_delete_elem()
handlers.
Before:
# bpftool p d x i 1
0: (bf) r2 = r10
1: (07) r2 += -8
2: (7a) *(u64 *)(r2 +0) = 0
3: (18) r1 = map[id:1]
5: (85) call __htab_map_lookup_elem#232656
6: (15) if r0 == 0x0 goto pc+4
7: (71) r1 = *(u8 *)(r0 +35)
8: (55) if r1 != 0x0 goto pc+1
9: (72) *(u8 *)(r0 +35) = 1
10: (07) r0 += 56
11: (15) if r0 == 0x0 goto pc+4
12: (bf) r2 = r0
13: (18) r1 = map[id:1]
15: (85) call bpf_map_delete_elem#215008 <-- indirect call via
16: (95) exit helper
After:
# bpftool p d x i 1
0: (bf) r2 = r10
1: (07) r2 += -8
2: (7a) *(u64 *)(r2 +0) = 0
3: (18) r1 = map[id:1]
5: (85) call __htab_map_lookup_elem#233328
6: (15) if r0 == 0x0 goto pc+4
7: (71) r1 = *(u8 *)(r0 +35)
8: (55) if r1 != 0x0 goto pc+1
9: (72) *(u8 *)(r0 +35) = 1
10: (07) r0 += 56
11: (15) if r0 == 0x0 goto pc+4
12: (bf) r2 = r0
13: (18) r1 = map[id:1]
15: (85) call htab_lru_map_delete_elem#238240 <-- direct call
16: (95) exit
In all three lookup/update/delete cases however we can use the actual
address of the map callback directly if we find that there's only a
single path with a map pointer leading to the helper call, meaning
when the map pointer has not been poisoned from verifier side.
Example code can be seen above for the delete case.
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Alexei Starovoitov <ast@...nel.org>
---
include/linux/filter.h | 3 +++
kernel/bpf/hashtab.c | 12 ++++++---
kernel/bpf/verifier.c | 67 +++++++++++++++++++++++++++++++++++++-------------
3 files changed, 62 insertions(+), 20 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index b443f70..d407ede 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -301,6 +301,9 @@ struct xdp_buff;
/* Function call */
+#define BPF_CAST_CALL(x) \
+ ((u64 (*)(u64, u64, u64, u64, u64))(x))
+
#define BPF_EMIT_CALL(FUNC) \
((struct bpf_insn) { \
.code = BPF_JMP | BPF_CALL, \
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index b76828f..3ca2198 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -503,7 +503,9 @@ static u32 htab_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
struct bpf_insn *insn = insn_buf;
const int ret = BPF_REG_0;
- *insn++ = BPF_EMIT_CALL((u64 (*)(u64, u64, u64, u64, u64))__htab_map_lookup_elem);
+ BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
+ (void *(*)(struct bpf_map *map, void *key))NULL));
+ *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 1);
*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
offsetof(struct htab_elem, key) +
@@ -530,7 +532,9 @@ static u32 htab_lru_map_gen_lookup(struct bpf_map *map,
const int ret = BPF_REG_0;
const int ref_reg = BPF_REG_1;
- *insn++ = BPF_EMIT_CALL((u64 (*)(u64, u64, u64, u64, u64))__htab_map_lookup_elem);
+ BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
+ (void *(*)(struct bpf_map *map, void *key))NULL));
+ *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 4);
*insn++ = BPF_LDX_MEM(BPF_B, ref_reg, ret,
offsetof(struct htab_elem, lru_node) +
@@ -1369,7 +1373,9 @@ static u32 htab_of_map_gen_lookup(struct bpf_map *map,
struct bpf_insn *insn = insn_buf;
const int ret = BPF_REG_0;
- *insn++ = BPF_EMIT_CALL((u64 (*)(u64, u64, u64, u64, u64))__htab_map_lookup_elem);
+ BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
+ (void *(*)(struct bpf_map *map, void *key))NULL));
+ *insn++ = BPF_EMIT_CALL(BPF_CAST_CALL(__htab_map_lookup_elem));
*insn++ = BPF_JMP_IMM(BPF_JEQ, ret, 0, 2);
*insn++ = BPF_ALU64_IMM(BPF_ADD, ret,
offsetof(struct htab_elem, key) +
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4f4786e..5684b15 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2421,8 +2421,11 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
struct bpf_insn_aux_data *aux = &env->insn_aux_data[insn_idx];
if (func_id != BPF_FUNC_tail_call &&
- func_id != BPF_FUNC_map_lookup_elem)
+ func_id != BPF_FUNC_map_lookup_elem &&
+ func_id != BPF_FUNC_map_update_elem &&
+ func_id != BPF_FUNC_map_delete_elem)
return 0;
+
if (meta->map_ptr == NULL) {
verbose(env, "kernel subsystem misconfigured verifier\n");
return -EINVAL;
@@ -5586,6 +5589,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
struct bpf_insn *insn = prog->insnsi;
const struct bpf_func_proto *fn;
const int insn_cnt = prog->len;
+ const struct bpf_map_ops *ops;
struct bpf_insn_aux_data *aux;
struct bpf_insn insn_buf[16];
struct bpf_prog *new_prog;
@@ -5715,10 +5719,13 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
}
/* BPF_EMIT_CALL() assumptions in some of the map_gen_lookup
- * handlers are currently limited to 64 bit only.
+ * and other inlining handlers are currently limited to 64 bit
+ * only.
*/
if (prog->jit_requested && BITS_PER_LONG == 64 &&
- insn->imm == BPF_FUNC_map_lookup_elem) {
+ (insn->imm == BPF_FUNC_map_lookup_elem ||
+ insn->imm == BPF_FUNC_map_update_elem ||
+ insn->imm == BPF_FUNC_map_delete_elem)) {
aux = &env->insn_aux_data[i + delta];
if (bpf_map_ptr_poisoned(aux))
goto patch_call_imm;
@@ -5727,23 +5734,49 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
if (!map_ptr->ops->map_gen_lookup)
goto patch_call_imm;
- cnt = map_ptr->ops->map_gen_lookup(map_ptr, insn_buf);
- if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
- verbose(env, "bpf verifier is misconfigured\n");
- return -EINVAL;
- }
+ ops = map_ptr->ops;
+ if (insn->imm == BPF_FUNC_map_lookup_elem &&
+ ops->map_gen_lookup) {
+ cnt = ops->map_gen_lookup(map_ptr, insn_buf);
+ if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
+ verbose(env, "bpf verifier is misconfigured\n");
+ return -EINVAL;
+ }
- new_prog = bpf_patch_insn_data(env, i + delta, insn_buf,
- cnt);
- if (!new_prog)
- return -ENOMEM;
+ new_prog = bpf_patch_insn_data(env, i + delta,
+ insn_buf, cnt);
+ if (!new_prog)
+ return -ENOMEM;
- delta += cnt - 1;
+ delta += cnt - 1;
+ env->prog = prog = new_prog;
+ insn = new_prog->insnsi + i + delta;
+ continue;
+ }
- /* keep walking new program and skip insns we just inserted */
- env->prog = prog = new_prog;
- insn = new_prog->insnsi + i + delta;
- continue;
+ BUILD_BUG_ON(!__same_type(ops->map_lookup_elem,
+ (void *(*)(struct bpf_map *map, void *key))NULL));
+ BUILD_BUG_ON(!__same_type(ops->map_delete_elem,
+ (int (*)(struct bpf_map *map, void *key))NULL));
+ BUILD_BUG_ON(!__same_type(ops->map_update_elem,
+ (int (*)(struct bpf_map *map, void *key, void *value,
+ u64 flags))NULL));
+ switch (insn->imm) {
+ case BPF_FUNC_map_lookup_elem:
+ insn->imm = BPF_CAST_CALL(ops->map_lookup_elem) -
+ __bpf_call_base;
+ continue;
+ case BPF_FUNC_map_update_elem:
+ insn->imm = BPF_CAST_CALL(ops->map_update_elem) -
+ __bpf_call_base;
+ continue;
+ case BPF_FUNC_map_delete_elem:
+ insn->imm = BPF_CAST_CALL(ops->map_delete_elem) -
+ __bpf_call_base;
+ continue;
+ }
+
+ goto patch_call_imm;
}
if (insn->imm == BPF_FUNC_redirect_map) {
--
2.9.5
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