linux-kernel - [PATCH net-next 1/6] bpf: support 8-byte metafield access

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Date:   Fri, 26 Aug 2016 19:31:19 -0700
From:   Alexei Starovoitov <ast@...com>
To:     "David S . Miller" <davem@...emloft.net>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Brendan Gregg <bgregg@...flix.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        Wang Nan <wangnan0@...wei.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...com>
Subject: [PATCH net-next 1/6] bpf: support 8-byte metafield access

The verifier supported only 4-byte metafields in
struct __sk_buff and struct xdp_md. The metafields in upcoming
struct bpf_perf_event are 8-byte to match register width in struct pt_regs.
Teach verifier to recognize 8-byte metafield access.
The patch doesn't affect safety of sockets and xdp programs.
They check for 4-byte only ctx access before these conditions are hit.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
---
 kernel/bpf/verifier.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index abb61f3f6900..c1c9e441f0f5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2333,7 +2333,8 @@ static int do_check(struct verifier_env *env)
 			if (err)
 				return err;
 
-			if (BPF_SIZE(insn->code) != BPF_W) {
+			if (BPF_SIZE(insn->code) != BPF_W &&
+			    BPF_SIZE(insn->code) != BPF_DW) {
 				insn_idx++;
 				continue;
 			}
@@ -2642,9 +2643,11 @@ static int convert_ctx_accesses(struct verifier_env *env)
 	for (i = 0; i < insn_cnt; i++, insn++) {
 		u32 insn_delta, cnt;
 
-		if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
+		if (insn->code == (BPF_LDX | BPF_MEM | BPF_W) ||
+		    insn->code == (BPF_LDX | BPF_MEM | BPF_DW))
 			type = BPF_READ;
-		else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
+		else if (insn->code == (BPF_STX | BPF_MEM | BPF_W) ||
+			 insn->code == (BPF_STX | BPF_MEM | BPF_DW))
 			type = BPF_WRITE;
 		else
 			continue;
-- 
2.8.0