netdev - [PATCHv6 net-next 07/15] bpf: recognize 64bit immediate loads as consts

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Message-Id: <1474211365-20088-8-git-send-email-jakub.kicinski@netronome.com>
Date:   Sun, 18 Sep 2016 16:09:17 +0100
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     netdev@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCHv6 net-next 07/15] bpf: recognize 64bit immediate loads as consts

When running as parser interpret BPF_LD | BPF_IMM | BPF_DW
instructions as loading CONST_IMM with the value stored
in imm.  The verifier will continue not recognizing those
due to concerns about search space/program complexity
increase.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Acked-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
---
v3:
 - limit to parsers.
---
 kernel/bpf/verifier.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ff03cd07f761..1612f7364c42 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1760,9 +1760,19 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	if (err)
 		return err;
 
-	if (insn->src_reg == 0)
-		/* generic move 64-bit immediate into a register */
+	if (insn->src_reg == 0) {
+		/* generic move 64-bit immediate into a register,
+		 * only analyzer needs to collect the ld_imm value.
+		 */
+		u64 imm = ((u64)(insn + 1)->imm << 32) | (u32)insn->imm;
+
+		if (!env->analyzer_ops)
+			return 0;
+
+		regs[insn->dst_reg].type = CONST_IMM;
+		regs[insn->dst_reg].imm = imm;
 		return 0;
+	}
 
 	/* replace_map_fd_with_map_ptr() should have caught bad ld_imm64 */
 	BUG_ON(insn->src_reg != BPF_PSEUDO_MAP_FD);
-- 
1.9.1