* FAILED: patch "[PATCH] bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX" failed to apply to 5.4-stable tree
@ 2020-04-30 15:06 gregkh
2020-04-30 23:03 ` Sasha Levin
0 siblings, 1 reply; 2+ messages in thread
From: gregkh @ 2020-04-30 15:06 UTC (permalink / raw)
To: lukenels, ast, luke.r.nels, xi.wang; +Cc: stable
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@vger.kernel.org>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From aee194b14dd2b2bde6252b3acf57d36dccfc743a Mon Sep 17 00:00:00 2001
From: Luke Nelson <lukenels@cs.washington.edu>
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@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200418232655.23870-1-luke.r.nels@gmail.com
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 5ea7c2cf7ab4..42b6709e6dc7 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -158,6 +158,19 @@ static bool is_ereg(u32 reg)
BIT(BPF_REG_AX));
}
+/*
+ * is_ereg_8l() == true if BPF register 'reg' is mapped to access x86-64
+ * lower 8-bit registers dil,sil,bpl,spl,r8b..r15b, which need extra byte
+ * of encoding. al,cl,dl,bl have simpler encoding.
+ */
+static bool is_ereg_8l(u32 reg)
+{
+ return is_ereg(reg) ||
+ (1 << reg) & (BIT(BPF_REG_1) |
+ BIT(BPF_REG_2) |
+ BIT(BPF_REG_FP));
+}
+
static bool is_axreg(u32 reg)
{
return reg == BPF_REG_0;
@@ -598,9 +611,8 @@ static void emit_stx(u8 **pprog, u32 size, u32 dst_reg, u32 src_reg, int off)
switch (size) {
case BPF_B:
/* Emit 'mov byte ptr [rax + off], al' */
- if (is_ereg(dst_reg) || is_ereg(src_reg) ||
- /* We have to add extra byte for x86 SIL, DIL regs */
- src_reg == BPF_REG_1 || src_reg == BPF_REG_2)
+ if (is_ereg(dst_reg) || is_ereg_8l(src_reg))
+ /* Add extra byte for eregs or SIL,DIL,BPL in src_reg */
EMIT2(add_2mod(0x40, dst_reg, src_reg), 0x88);
else
EMIT1(0x88);
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: FAILED: patch "[PATCH] bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX" failed to apply to 5.4-stable tree
2020-04-30 15:06 FAILED: patch "[PATCH] bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX" failed to apply to 5.4-stable tree gregkh
@ 2020-04-30 23:03 ` Sasha Levin
0 siblings, 0 replies; 2+ messages in thread
From: Sasha Levin @ 2020-04-30 23:03 UTC (permalink / raw)
To: gregkh; +Cc: lukenels, ast, luke.r.nels, xi.wang, stable
On Thu, Apr 30, 2020 at 05:06:18PM +0200, gregkh@linuxfoundation.org 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@vger.kernel.org>.
>
>thanks,
>
>greg k-h
>
>------------------ original commit in Linus's tree ------------------
>
>From aee194b14dd2b2bde6252b3acf57d36dccfc743a Mon Sep 17 00:00:00 2001
>From: Luke Nelson <lukenels@cs.washington.edu>
>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@gmail.com>
>Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
>Signed-off-by: Alexei Starovoitov <ast@kernel.org>
>Link: https://lore.kernel.org/bpf/20200418232655.23870-1-luke.r.nels@gmail.com
The code got shuffled around in 3b2744e66520 ("bpf: Refactor x86 JIT
into helpers"). I've fixed it and queued for all branches.
--
Thanks,
Sasha
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-04-30 15:06 FAILED: patch "[PATCH] bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX" failed to apply to 5.4-stable tree gregkh
2020-04-30 23:03 ` Sasha Levin
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