This is a note to let you know that I've just added the patch titled
bpf: Fix precision tracking for BPF_ALU | BPF_TO_BE | BPF_END
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-fix-precision-tracking-for-bpf_alu-bpf_to_be-bpf_end.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 291d044fd51f8484066300ee42afecf8c8db7b3a Mon Sep 17 00:00:00 2001
From: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
Date: Thu, 2 Nov 2023 13:39:03 +0800
Subject: bpf: Fix precision tracking for BPF_ALU | BPF_TO_BE | BPF_END
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From: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
commit 291d044fd51f8484066300ee42afecf8c8db7b3a upstream.
BPF_END and BPF_NEG has a different specification for the source bit in
the opcode compared to other ALU/ALU64 instructions, and is either
reserved or use to specify the byte swap endianness. In both cases the
source bit does not encode source operand location, and src_reg is a
reserved field.
backtrack_insn() currently does not differentiate BPF_END and BPF_NEG
from other ALU/ALU64 instructions, which leads to r0 being incorrectly
marked as precise when processing BPF_ALU | BPF_TO_BE | BPF_END
instructions. This commit teaches backtrack_insn() to correctly mark
precision for such case.
While precise tracking of BPF_NEG and other BPF_END instructions are
correct and does not need fixing, this commit opt to process all BPF_NEG
and BPF_END instructions within the same if-clause to better align with
current convention used in the verifier (e.g. check_alu_op).
Fixes: b5dc0163d8fd ("bpf: precise scalar_value tracking")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Mohamed Mahmoud <mmahmoud@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/87jzrrwptf.fsf@xxxxxxx
Tested-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Tested-by: Tao Lyu <tao.lyu@xxxxxxx>
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
Link: https://lore.kernel.org/r/20231102053913.12004-2-shung-hsi.yu@xxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/bpf/verifier.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1469,7 +1469,12 @@ static int backtrack_insn(struct bpf_ver
if (class == BPF_ALU || class == BPF_ALU64) {
if (!(*reg_mask & dreg))
return 0;
- if (opcode == BPF_MOV) {
+ if (opcode == BPF_END || opcode == BPF_NEG) {
+ /* sreg is reserved and unused
+ * dreg still need precision before this insn
+ */
+ return 0;
+ } else if (opcode == BPF_MOV) {
if (BPF_SRC(insn->code) == BPF_X) {
/* dreg = sreg
* dreg needs precision after this insn
Patches currently in stable-queue which might be from shung-hsi.yu@xxxxxxxx are
queue-5.4/bpf-fix-precision-tracking-for-bpf_alu-bpf_to_be-bpf_end.patch
