From: Alexei Starovoitov <ast@kernel.org>
To: <davem@davemloft.net>
Cc: <daniel@iogearbox.net>, <andriin@fb.com>,
<netdev@vger.kernel.org>, <bpf@vger.kernel.org>,
<kernel-team@fb.com>
Subject: [PATCH v2 bpf-next 3/9] bpf: extend is_branch_taken to registers
Date: Fri, 14 Jun 2019 00:25:51 -0700 [thread overview]
Message-ID: <20190614072557.196239-4-ast@kernel.org> (raw)
In-Reply-To: <20190614072557.196239-1-ast@kernel.org>
This patch extends is_branch_taken() logic from JMP+K instructions
to JMP+X instructions.
Conditional branches are often done when src and dst registers
contain known scalars. In such case the verifier can follow
the branch that is going to be taken when program executes.
That speeds up the verification and is essential feature to support
bounded loops.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
kernel/bpf/verifier.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6c13d86569a6..8d3a4ef1d969 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5266,9 +5266,10 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
struct bpf_verifier_state *this_branch = env->cur_state;
struct bpf_verifier_state *other_branch;
struct bpf_reg_state *regs = this_branch->frame[this_branch->curframe]->regs;
- struct bpf_reg_state *dst_reg, *other_branch_regs;
+ struct bpf_reg_state *dst_reg, *other_branch_regs, *src_reg = NULL;
u8 opcode = BPF_OP(insn->code);
bool is_jmp32;
+ int pred = -1;
int err;
/* Only conditional jumps are expected to reach here. */
@@ -5293,6 +5294,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
insn->src_reg);
return -EACCES;
}
+ src_reg = ®s[insn->src_reg];
} else {
if (insn->src_reg != BPF_REG_0) {
verbose(env, "BPF_JMP/JMP32 uses reserved fields\n");
@@ -5308,20 +5310,22 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
dst_reg = ®s[insn->dst_reg];
is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
- if (BPF_SRC(insn->code) == BPF_K) {
- int pred = is_branch_taken(dst_reg, insn->imm, opcode,
- is_jmp32);
-
- if (pred == 1) {
- /* only follow the goto, ignore fall-through */
- *insn_idx += insn->off;
- return 0;
- } else if (pred == 0) {
- /* only follow fall-through branch, since
- * that's where the program will go
- */
- return 0;
- }
+ if (BPF_SRC(insn->code) == BPF_K)
+ pred = is_branch_taken(dst_reg, insn->imm,
+ opcode, is_jmp32);
+ else if (src_reg->type == SCALAR_VALUE &&
+ tnum_is_const(src_reg->var_off))
+ pred = is_branch_taken(dst_reg, src_reg->var_off.value,
+ opcode, is_jmp32);
+ if (pred == 1) {
+ /* only follow the goto, ignore fall-through */
+ *insn_idx += insn->off;
+ return 0;
+ } else if (pred == 0) {
+ /* only follow fall-through branch, since
+ * that's where the program will go
+ */
+ return 0;
}
other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx,
--
2.20.0
next prev parent reply other threads:[~2019-06-14 7:26 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-14 7:25 [PATCH v2 bpf-next 0/9] bpf: bounded loops and other features Alexei Starovoitov
2019-06-14 7:25 ` [PATCH v2 bpf-next 1/9] bpf: track spill/fill of constants Alexei Starovoitov
2019-06-14 16:29 ` Andrii Nakryiko
2019-06-14 7:25 ` [PATCH v2 bpf-next 2/9] selftests/bpf: fix tests due to const spill/fill Alexei Starovoitov
2019-06-14 7:25 ` Alexei Starovoitov [this message]
2019-06-14 16:38 ` [PATCH v2 bpf-next 3/9] bpf: extend is_branch_taken to registers Andrii Nakryiko
2019-06-14 7:25 ` [PATCH v2 bpf-next 4/9] bpf: introduce bounded loops Alexei Starovoitov
2019-06-14 7:25 ` [PATCH v2 bpf-next 5/9] bpf: fix callees pruning callers Alexei Starovoitov
2019-06-14 7:25 ` [PATCH v2 bpf-next 6/9] selftests/bpf: fix tests Alexei Starovoitov
2019-06-14 7:25 ` [PATCH v2 bpf-next 7/9] selftests/bpf: add basic verifier tests for loops Alexei Starovoitov
2019-06-14 7:25 ` [PATCH v2 bpf-next 8/9] selftests/bpf: add realistic loop tests Alexei Starovoitov
2019-06-14 16:49 ` Andrii Nakryiko
2019-06-14 7:25 ` [PATCH v2 bpf-next 9/9] bpf: precise scalar_value tracking Alexei Starovoitov
2019-06-14 21:45 ` Andrii Nakryiko
2019-06-15 19:00 ` Alexei Starovoitov
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