On Thu, Apr 30, 2020 at 05:06:18PM +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From aee194b14dd2b2bde6252b3acf57d36dccfc743a Mon Sep 17 00:00:00 2001
From: Luke Nelson <lukenels@xxxxxxxxxxxxxxxxx>
Date: Sat, 18 Apr 2020 16:26:53 -0700
Subject: [PATCH] bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX
BPF_B
This patch fixes an encoding bug in emit_stx for BPF_B when the source
register is BPF_REG_FP.
The current implementation for BPF_STX BPF_B in emit_stx saves one REX
byte when the operands can be encoded using Mod-R/M alone. The lower 8
bits of registers %rax, %rbx, %rcx, and %rdx can be accessed without using
a REX prefix via %al, %bl, %cl, and %dl, respectively. Other registers,
(e.g., %rsi, %rdi, %rbp, %rsp) require a REX prefix to use their 8-bit
equivalents (%sil, %dil, %bpl, %spl).
The current code checks if the source for BPF_STX BPF_B is BPF_REG_1
or BPF_REG_2 (which map to %rdi and %rsi), in which case it emits the
required REX prefix. However, it misses the case when the source is
BPF_REG_FP (mapped to %rbp).
The result is that BPF_STX BPF_B with BPF_REG_FP as the source operand
will read from register %ch instead of the correct %bpl. This patch fixes
the problem by fixing and refactoring the check on which registers need
the extra REX byte. Since no BPF registers map to %rsp, there is no need
to handle %spl.
Fixes: 622582786c9e0 ("net: filter: x86: internal BPF JIT")
Signed-off-by: Xi Wang <xi.wang@xxxxxxxxx>
Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20200418232655.23870-1-luke.r.nels@xxxxxxxxx
The code got shuffled around in 3b2744e66520 ("bpf: Refactor x86 JIT
into helpers"). I've fixed it and queued for all branches.
--
Thanks,
Sasha
