Two BPF fixes for s390

Found while testing some other work touching JITs.

Thanks!

Daniel Borkmann (2):
bpf, s390: fix jit branch offset related to ldimm64 bpf, s390: fix build for libbpf and selftest suite

 arch/s390/net/bpf_jit_comp.c   | 3 ++-
 tools/build/feature/test-bpf.c | 2 ++
 tools/lib/bpf/bpf.c            | 2 ++
 3 files changed, 6 insertions(+), 1 deletion(-)

1.9.3

While testing some other work that required JIT modifications, I run into test_bpf causing a hang when JIT enabled on s390. The problematic test case was the one from ddc665a4bb4b (bpf, arm64:
fix jit branch offset related to ldimm64), and turns out that we do have a similar issue on s390 as well. In bpf_jit_prog() we update next instruction address after returning from bpf_jit_insn() with an insn_count. bpf_jit_insn() returns either -1 in case of error (e.g. unsupported insn), 1 or 2. The latter is only the case for ldimm64 due to spanning 2 insns, however, next address is only set to i + 1 not taking actual insn_count into account, thus fix is to use insn_count instead of 1. bpf_jit_enable in mode 2 provides also disasm on s390:

Before fix:

  000003ff800349b6: a7f40003   brc     15,3ff800349bc                 ; target
  000003ff800349ba: 0000               unknown
  000003ff800349bc: e3b0f0700024       stg     %r11,112(%r15)
  000003ff800349c2: e3e0f0880024       stg     %r14,136(%r15)
  000003ff800349c8: 0db0               basr    %r11,%r0
  000003ff800349ca: c0ef00000000       llilf   %r14,0
  000003ff800349d0: e320b0360004       lg      %r2,54(%r11)
  000003ff800349d6: e330b03e0004       lg      %r3,62(%r11)
  000003ff800349dc: ec23ffeda065       clgrj   %r2,%r3,10,3ff800349b6 ; jmp
  000003ff800349e2: e3e0b0460004       lg      %r14,70(%r11)
  000003ff800349e8: e3e0b04e0004       lg      %r14,78(%r11)
  000003ff800349ee: b904002e   lgr     %r2,%r14
  000003ff800349f2: e3b0f0700004       lg      %r11,112(%r15)
  000003ff800349f8: e3e0f0880004       lg      %r14,136(%r15)
  000003ff800349fe: 07fe               bcr     15,%r14

After fix:

  000003ff80ef3db4: a7f40003   brc     15,3ff80ef3dba
  000003ff80ef3db8: 0000               unknown
  000003ff80ef3dba: e3b0f0700024       stg     %r11,112(%r15)
  000003ff80ef3dc0: e3e0f0880024       stg     %r14,136(%r15)
  000003ff80ef3dc6: 0db0               basr    %r11,%r0
  000003ff80ef3dc8: c0ef00000000       llilf   %r14,0
  000003ff80ef3dce: e320b0360004       lg      %r2,54(%r11)
  000003ff80ef3dd4: e330b03e0004       lg      %r3,62(%r11)
  000003ff80ef3dda: ec230006a065       clgrj   %r2,%r3,10,3ff80ef3de6 ; jmp
  000003ff80ef3de0: e3e0b0460004       lg      %r14,70(%r11)
  000003ff80ef3de6: e3e0b04e0004       lg      %r14,78(%r11)          ; target
  000003ff80ef3dec: b904002e   lgr     %r2,%r14
  000003ff80ef3df0: e3b0f0700004       lg      %r11,112(%r15)
  000003ff80ef3df6: e3e0f0880004       lg      %r14,136(%r15)
  000003ff80ef3dfc: 07fe               bcr     15,%r14

test_bpf.ko suite runs fine after the fix.

---
 arch/s390/net/bpf_jit_comp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 01c6fbc..1803797 100644
@@ -1253,7 +1253,8 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp)
 		insn_count = bpf_jit_insn(jit, fp, i);
 		if (insn_count < 0)
 			return -1;
-		jit->addrs[i + 1] = jit->prg; /* Next instruction address */
+		/* Next instruction address */
+		jit->addrs[i + insn_count] = jit->prg;
 	}
 	bpf_jit_epilogue(jit);
 

1.9.3

Am Fri, 4 Aug 2017 14:20:54 +0200
schrieb Daniel Borkmann <[email protected]>:

What about "Cc: [email protected]"?

Michael

[...]

Handled by Dave, see also: Documentation/networking/netdev-FAQ.txt +117

Cheers,
Daniel

Am Fri, 04 Aug 2017 15:52:47 +0200
schrieb Daniel Borkmann <[email protected]>:

Thanks, good to know! At least I would vote for "Cc: stable".

Michael

From: Michael Holzheu <[email protected]>
Date: Fri, 4 Aug 2017 19:10:33 +0200

No, please do not ever do this for networking patches.

The BPF feature test as well as libbpf is missing the __NR_bpf define for s390 and currently refuses to compile (selftest suite depends on libbpf as well). Similar issue was fixed some time ago via b0c47807d31d ("bpf: Add sparc support to tools and samples."), just do the same and add definitions.

---
 tools/build/feature/test-bpf.c | 2 ++
 tools/lib/bpf/bpf.c            | 2 ++
 2 files changed, 4 insertions(+)

index 7598361..da2172f 100644
@@ -11,6 +11,8 @@
 #  define __NR_bpf 280
 # elif defined(__sparc__)
 #  define __NR_bpf 349
+# elif defined(__s390__)
+#  define __NR_bpf 351
 # else
 #  error __NR_bpf not defined. libbpf does not support your arch.
 # endif

index 256f571..e5bbb09 100644
@@ -39,6 +39,8 @@
 #  define __NR_bpf 280
 # elif defined(__sparc__)
 #  define __NR_bpf 349
+# elif defined(__s390__)
+#  define __NR_bpf 351
 # else
 #  error __NR_bpf not defined. libbpf does not support your arch.
 # endif

1.9.3

From: Daniel Borkmann <[email protected]>
Date: Fri, 4 Aug 2017 14:20:53 +0200

Series applied and patch #1 queued up for -stable, thanks!