[PATCH net 1/2] s390/bpf: fix stack allocation

[PATCH net 1/2] s390/bpf: fix stack allocation

[Alexei Starovoitov]

From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

On s390x we have to provide 160 bytes stack space before we can call
the next function. From the 160 bytes that we got from the previous
function we only use 11 * 8 bytes and have 160 - 11 * 8 bytes left.
Currently for BPF we allocate additional 160 - 11 * 8 bytes for the
next function. This is wrong because then the next function only gets:

 (160 - 11 * 8) + (160 - 11 * 8) = 2 * 72 = 144 bytes

Fix this and allocate enough memory for the next function.

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---

Resubmitting against 'net' with proper 'Fixes' tag.

 arch/s390/net/bpf_jit.h |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/s390/net/bpf_jit.h b/arch/s390/net/bpf_jit.h
index ba8593a515ba..de156ba3bd71 100644
--- a/arch/s390/net/bpf_jit.h
+++ b/arch/s390/net/bpf_jit.h
@@ -48,7 +48,9 @@ extern u8 sk_load_word[], sk_load_half[], sk_load_byte[];
  * We get 160 bytes stack space from calling function, but only use
  * 11 * 8 byte (old backchain + r15 - r6) for storing registers.
  */
-#define STK_OFF (MAX_BPF_STACK + 8 + 4 + 4 + (160 - 11 * 8))
+#define STK_SPACE	(MAX_BPF_STACK + 8 + 4 + 4 + 160)
+#define STK_160_UNUSED	(160 - 11 * 8)
+#define STK_OFF		(STK_SPACE - STK_160_UNUSED)
 #define STK_OFF_TMP	160	/* Offset of tmp buffer on stack */
 #define STK_OFF_HLEN	168	/* Offset of SKB header length on stack */
 
-- 
1.7.9.5

[PATCH net 2/2] s390/bpf: fix bpf frame pointer setup

[Alexei Starovoitov]

From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

Currently the bpf frame pointer is set to the old r15. This is
wrong because of packed stack. Fix this and adjust the frame pointer
to respect packed stack. This now generates a prolog like the following:

 3ff8001c3fa: eb67f0480024   stmg    %r6,%r7,72(%r15)
 3ff8001c400: ebcff0780024   stmg    %r12,%r15,120(%r15)
 3ff8001c406: b904001f       lgr     %r1,%r15      <- load backchain
 3ff8001c40a: 41d0f048       la      %r13,72(%r15) <- load adjusted bfp
 3ff8001c40e: a7fbfd98       aghi    %r15,-616
 3ff8001c412: e310f0980024   stg     %r1,152(%r15) <- save backchain

Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
 arch/s390/net/bpf_jit_comp.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 20c146d1251a..55423d8be580 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -384,13 +384,16 @@ static void bpf_jit_prologue(struct bpf_jit *jit)
 	}
 	/* Setup stack and backchain */
 	if (jit->seen & SEEN_STACK) {
-		/* lgr %bfp,%r15 (BPF frame pointer) */
-		EMIT4(0xb9040000, BPF_REG_FP, REG_15);
+		if (jit->seen & SEEN_FUNC)
+			/* lgr %w1,%r15 (backchain) */
+			EMIT4(0xb9040000, REG_W1, REG_15);
+		/* la %bfp,STK_160_UNUSED(%r15) (BPF frame pointer) */
+		EMIT4_DISP(0x41000000, BPF_REG_FP, REG_15, STK_160_UNUSED);
 		/* aghi %r15,-STK_OFF */
 		EMIT4_IMM(0xa70b0000, REG_15, -STK_OFF);
 		if (jit->seen & SEEN_FUNC)
-			/* stg %bfp,152(%r15) (backchain) */
-			EMIT6_DISP_LH(0xe3000000, 0x0024, BPF_REG_FP, REG_0,
+			/* stg %w1,152(%r15) (backchain) */
+			EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0,
 				      REG_15, 152);
 	}
 	/*
-- 
1.7.9.5

Re: [PATCH net 1/2] s390/bpf: fix stack allocation

[David Miller]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Mon,  1 Jun 2015 22:48:34 -0700

> From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> 
> On s390x we have to provide 160 bytes stack space before we can call
> the next function. From the 160 bytes that we got from the previous
> function we only use 11 * 8 bytes and have 160 - 11 * 8 bytes left.
> Currently for BPF we allocate additional 160 - 11 * 8 bytes for the
> next function. This is wrong because then the next function only gets:
> 
>  (160 - 11 * 8) + (160 - 11 * 8) = 2 * 72 = 144 bytes
> 
> Fix this and allocate enough memory for the next function.
> 
> Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
> Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>

Applied.

Re: [PATCH net 2/2] s390/bpf: fix bpf frame pointer setup

[David Miller]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Mon,  1 Jun 2015 22:48:35 -0700

> From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> 
> Currently the bpf frame pointer is set to the old r15. This is
> wrong because of packed stack. Fix this and adjust the frame pointer
> to respect packed stack. This now generates a prolog like the following:
> 
>  3ff8001c3fa: eb67f0480024   stmg    %r6,%r7,72(%r15)
>  3ff8001c400: ebcff0780024   stmg    %r12,%r15,120(%r15)
>  3ff8001c406: b904001f       lgr     %r1,%r15      <- load backchain
>  3ff8001c40a: 41d0f048       la      %r13,72(%r15) <- load adjusted bfp
>  3ff8001c40e: a7fbfd98       aghi    %r15,-616
>  3ff8001c412: e310f0980024   stg     %r1,152(%r15) <- save backchain
> 
> Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
> Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>

Applied.