2018-07-25 16:47:14

by Wang YanQing

Subject: [PATCH] bpf, x32: Fix regression caused by commit 24dea04767e6

Commit 24dea04767e6 ("bpf, x32: remove ld_abs/ld_ind")
removed the 4 /* Extra space for skb_copy_bits buffer */
from _STACK_SIZE, but it didn't fix the concerned code
in emit_prologue and emit_epilogue, and this error will
bring very strange kernel runtime errors.

This patch fix it.

Fixes: 24dea04767e6 ("bpf, x32: remove ld_abs/ld_ind")
Signed-off-by: Wang YanQing <[email protected]>
---
arch/x86/net/bpf_jit_comp32.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index 5579987..8f6cc71 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -1441,8 +1441,8 @@ static void emit_prologue(u8 **pprog, u32 stack_depth)

/* sub esp,STACK_SIZE */
EMIT2_off32(0x81, 0xEC, STACK_SIZE);
- /* sub ebp,SCRATCH_SIZE+4+12*/
- EMIT3(0x83, add_1reg(0xE8, IA32_EBP), SCRATCH_SIZE + 16);
+ /* sub ebp,SCRATCH_SIZE+12*/
+ EMIT3(0x83, add_1reg(0xE8, IA32_EBP), SCRATCH_SIZE + 12);
/* xor ebx,ebx */
EMIT2(0x31, add_2reg(0xC0, IA32_EBX, IA32_EBX));

@@ -1475,8 +1475,8 @@ static void emit_epilogue(u8 **pprog, u32 stack_depth)
/* mov edx,dword ptr [ebp+off]*/
EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EDX), STACK_VAR(r0[1]));

- /* add ebp,SCRATCH_SIZE+4+12*/
- EMIT3(0x83, add_1reg(0xC0, IA32_EBP), SCRATCH_SIZE + 16);
+ /* add ebp,SCRATCH_SIZE+12*/
+ EMIT3(0x83, add_1reg(0xC0, IA32_EBP), SCRATCH_SIZE + 12);

/* mov ebx,dword ptr [ebp-12]*/
EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EBX), -12);
--
1.8.5.6.2.g3d8a54e.dirty

2018-07-25 16:59:58

by Daniel Borkmann

Subject: Re: [PATCH] bpf, x32: Fix regression caused by commit 24dea04767e6

On 07/25/2018 06:46 PM, Wang YanQing wrote:
> Commit 24dea04767e6 ("bpf, x32: remove ld_abs/ld_ind")
> removed the 4 /* Extra space for skb_copy_bits buffer */
> from _STACK_SIZE, but it didn't fix the concerned code
> in emit_prologue and emit_epilogue, and this error will
> bring very strange kernel runtime errors.
>
> This patch fix it.
>
> Fixes: 24dea04767e6 ("bpf, x32: remove ld_abs/ld_ind")
> Signed-off-by: Wang YanQing <[email protected]>

Applied, thanks Wang!

2018-07-28 07:24:17

by Meelis Roos

Subject: Re: [PATCH] bpf, x32: Fix regression caused by commit 24dea04767e6

> Commit 24dea04767e6 ("bpf, x32: remove ld_abs/ld_ind")
> removed the 4 /* Extra space for skb_copy_bits buffer */
> from _STACK_SIZE, but it didn't fix the concerned code
> in emit_prologue and emit_epilogue, and this error will
> bring very strange kernel runtime errors.
>
> This patch fix it.

For the record:

Tested it on top of 4.18.0-rc6-00192-g864af0d40cdc on the affected
machine and it worked.

--
Meelis Roos ([email protected])