From: Alexei Starovoitov <ast@kernel.org>
To: <davem@davemloft.net>
Cc: <daniel@iogearbox.net>, <netdev@vger.kernel.org>,
<bpf@vger.kernel.org>, <kernel-team@fb.com>
Subject: [PATCH bpf-next 3/9] bpf: extend is_branch_taken to registers
Date: Wed, 12 Jun 2019 21:47:32 -0700 [thread overview]
Message-ID: <20190613044738.3858896-4-ast@kernel.org> (raw)
In-Reply-To: <20190613044738.3858896-1-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 on CPU.
That speeds up the verification and essential feature to support
bounded loops.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
kernel/bpf/verifier.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a21bafd7d931..c79c09586a9e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5263,10 +5263,11 @@ 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 err;
+ u64 cond_val;
/* Only conditional jumps are expected to reach here. */
if (opcode == BPF_JA || opcode > BPF_JSLE) {
@@ -5290,6 +5291,7 @@ 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");
@@ -5306,8 +5308,11 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
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);
+ int pred;
+
+ cond_val = insn->imm;
+check_taken:
+ pred = is_branch_taken(dst_reg, cond_val, opcode, is_jmp32);
if (pred == 1) {
/* only follow the goto, ignore fall-through */
@@ -5319,6 +5324,11 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
*/
return 0;
}
+ } else if (BPF_SRC(insn->code) == BPF_X &&
+ src_reg->type == SCALAR_VALUE &&
+ tnum_is_const(src_reg->var_off)) {
+ cond_val = src_reg->var_off.value;
+ goto check_taken;
}
other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx,
--
2.20.0
next prev parent reply other threads:[~2019-06-13 16:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-13 4:47 [PATCH bpf-next 0/9] bpf: bounded loops and other features Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 1/9] bpf: track spill/fill of constants Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 2/9] selftests/bpf: fix tests due to const spill/fill Alexei Starovoitov
2019-06-13 4:47 ` Alexei Starovoitov [this message]
2019-06-13 4:47 ` [PATCH bpf-next 4/9] bpf: introduce bounded loops Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 5/9] bpf: fix callees pruning callers Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 6/9] selftests/bpf: fix tests Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 7/9] selftests/bpf: add basic verifier tests for loops Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 8/9] selftests/bpf: add realistic loop tests Alexei Starovoitov
2019-06-13 4:47 ` [PATCH bpf-next 9/9] bpf: precise scalar_value tracking Alexei Starovoitov
-- strict thread matches above, loose matches on Subject: below --
2019-06-13 4:19 [PATCH bpf-next 0/9] bpf: bounded loops and other features Alexei Starovoitov
2019-06-13 4:19 ` [PATCH bpf-next 3/9] bpf: extend is_branch_taken to registers Alexei Starovoitov
2019-06-13 22:25 ` Andrii Nakryiko
2019-06-14 6:12 ` Alexei Starovoitov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190613044738.3858896-4-ast@kernel.org \
--to=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=kernel-team@fb.com \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).