* [PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET
@ 2020-05-01 3:19 Wang YanQing
2020-05-01 3:42 ` Wang YanQing
0 siblings, 1 reply; 3+ messages in thread
From: Wang YanQing @ 2020-05-01 3:19 UTC (permalink / raw)
To: stable; +Cc: gregkh, lukenels, ast, luke.r.nels, udknight, xi.wang, daniel, bpf
commit 50fe7ebb6475711c15b3397467e6424e20026d94 upstream.
The current JIT clobbers the destination register for BPF_JSET BPF_X
and BPF_K by using "and" and "or" instructions. This is fine when the
destination register is a temporary loaded from a register stored on
the stack but not otherwise.
This patch fixes the problem (for both BPF_K and BPF_X) by always loading
the destination register into temporaries since BPF_JSET should not
modify the destination register.
This bug may not be currently triggerable as BPF_REG_AX is the only
register not stored on the stack and the verifier uses it in a limited
way.
Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32")
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>
Acked-by: Wang YanQing <udknight@gmail.com>
Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com
Signed-off-by: Wang YanQing <udknight@gmail.com>
---
arch/x86/net/bpf_jit_comp32.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index 24d573b..7e7ca5d 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -1968,8 +1968,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
goto emit_cond_jmp_signed;
}
case BPF_JMP | BPF_JSET | BPF_X: {
- u8 dreg_lo = dstk ? IA32_EAX : dst_lo;
- u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
+ u8 dreg_lo = IA32_EAX;
+ u8 dreg_hi = IA32_EDX;
u8 sreg_lo = sstk ? IA32_ECX : src_lo;
u8 sreg_hi = sstk ? IA32_EBX : src_hi;
@@ -1978,6 +1978,12 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
STACK_VAR(dst_lo));
EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EDX),
STACK_VAR(dst_hi));
+ } else {
+ /* mov dreg_lo,dst_lo */
+ EMIT2(0x89, add_2reg(0xC0, dreg_lo, dst_lo));
+ /* mov dreg_hi,dst_hi */
+ EMIT2(0x89,
+ add_2reg(0xC0, dreg_hi, dst_hi));
}
if (sstk) {
@@ -1996,8 +2002,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
}
case BPF_JMP | BPF_JSET | BPF_K: {
u32 hi;
- u8 dreg_lo = dstk ? IA32_EAX : dst_lo;
- u8 dreg_hi = dstk ? IA32_EDX : dst_hi;
+ u8 dreg_lo = IA32_EAX;
+ u8 dreg_hi = IA32_EDX;
u8 sreg_lo = IA32_ECX;
u8 sreg_hi = IA32_EBX;
@@ -2006,6 +2012,12 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
STACK_VAR(dst_lo));
EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EDX),
STACK_VAR(dst_hi));
+ } else {
+ /* mov dreg_lo,dst_lo */
+ EMIT2(0x89, add_2reg(0xC0, dreg_lo, dst_lo));
+ /* mov dreg_hi,dst_hi */
+ EMIT2(0x89,
+ add_2reg(0xC0, dreg_hi, dst_hi));
}
hi = imm32 & (1<<31) ? (u32)~0 : 0;
--
1.8.5.6.2.g3d8a54e.dirty
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET
2020-05-01 3:19 [PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET Wang YanQing
@ 2020-05-01 3:42 ` Wang YanQing
2020-05-01 6:53 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: Wang YanQing @ 2020-05-01 3:42 UTC (permalink / raw)
To: stable; +Cc: gregkh, lukenels, ast, luke.r.nels, xi.wang, daniel, bpf
On Fri, May 01, 2020 at 11:19:50AM +0800, Wang YanQing wrote:
> commit 50fe7ebb6475711c15b3397467e6424e20026d94 upstream.
>
> The current JIT clobbers the destination register for BPF_JSET BPF_X
> and BPF_K by using "and" and "or" instructions. This is fine when the
> destination register is a temporary loaded from a register stored on
> the stack but not otherwise.
>
> This patch fixes the problem (for both BPF_K and BPF_X) by always loading
> the destination register into temporaries since BPF_JSET should not
> modify the destination register.
>
> This bug may not be currently triggerable as BPF_REG_AX is the only
> register not stored on the stack and the verifier uses it in a limited
> way.
>
> Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32")
> 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>
> Acked-by: Wang YanQing <udknight@gmail.com>
> Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com
> Signed-off-by: Wang YanQing <udknight@gmail.com>
Cc: stable@vger.kernel.org #v4.19
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET
2020-05-01 3:42 ` Wang YanQing
@ 2020-05-01 6:53 ` Greg KH
0 siblings, 0 replies; 3+ messages in thread
From: Greg KH @ 2020-05-01 6:53 UTC (permalink / raw)
To: Wang YanQing; +Cc: stable, lukenels, ast, luke.r.nels, xi.wang, daniel, bpf
On Fri, May 01, 2020 at 11:42:28AM +0800, Wang YanQing wrote:
> On Fri, May 01, 2020 at 11:19:50AM +0800, Wang YanQing wrote:
> > commit 50fe7ebb6475711c15b3397467e6424e20026d94 upstream.
> >
> > The current JIT clobbers the destination register for BPF_JSET BPF_X
> > and BPF_K by using "and" and "or" instructions. This is fine when the
> > destination register is a temporary loaded from a register stored on
> > the stack but not otherwise.
> >
> > This patch fixes the problem (for both BPF_K and BPF_X) by always loading
> > the destination register into temporaries since BPF_JSET should not
> > modify the destination register.
> >
> > This bug may not be currently triggerable as BPF_REG_AX is the only
> > register not stored on the stack and the verifier uses it in a limited
> > way.
> >
> > Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32")
> > 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>
> > Acked-by: Wang YanQing <udknight@gmail.com>
> > Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com
> > Signed-off-by: Wang YanQing <udknight@gmail.com>
> Cc: stable@vger.kernel.org #v4.19
Now queued up, thanks.
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-05-01 3:19 [PATCH] bpf, x86_32: Fix clobbering of dst for BPF_JSET Wang YanQing
2020-05-01 3:42 ` Wang YanQing
2020-05-01 6:53 ` Greg KH
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