netdev - [PATCH v3 bpf-next 3/9] bpf: extend is_branch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190615191225.2409862-4-ast@kernel.org>
Date:   Sat, 15 Jun 2019 12:12:19 -0700
From:   Alexei Starovoitov <ast@...nel.org>
To:     <davem@...emloft.net>
CC:     <daniel@...earbox.net>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <kernel-team@...com>
Subject: [PATCH v3 bpf-next 3/9] bpf: extend is_branch_taken to registers

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@...nel.org>
Acked-by: Andrii Nakryiko <andriin@...com>
---
 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 = &regs[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 = &regs[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