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From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>
Cc: bpf@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	Seth Forshee <seth.forshee@canonical.com>
Subject: [PATCH 2/5] s390/bpf: fix sign extension in branch_ku
Date: Fri, 17 Jul 2020 18:53:23 +0200	[thread overview]
Message-ID: <20200717165326.6786-3-iii@linux.ibm.com> (raw)
In-Reply-To: <20200717165326.6786-1-iii@linux.ibm.com>

Both signed and unsigned variants of BPF_JMP | BPF_K require
sign-extending the immediate. JIT emits cgfi for the signed case,
which is correct, and clgfi for the unsigned case, which is not
correct: clgfi zero-extends the immediate.

s390 does not provide an instruction that does sign-extension and
unsigned comparison at the same time. Therefore, fix by first loading
the sign-extended immediate into work register REG_1 and proceeding
as if it's BPF_X.

Fixes: 4e9b4a6883dd ("s390/bpf: Use relative long branches")
Reported-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/net/bpf_jit_comp.c | 19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 8fe7bdfc8d15..67608f6092f8 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1507,21 +1507,10 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		}
 		break;
 branch_ku:
-		is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
-		/* clfi or clgfi %dst,imm */
-		EMIT6_IMM(is_jmp32 ? 0xc20f0000 : 0xc20e0000,
-			  dst_reg, imm);
-		if (!is_first_pass(jit) &&
-		    can_use_rel(jit, addrs[i + off + 1])) {
-			/* brc mask,off */
-			EMIT4_PCREL_RIC(0xa7040000,
-					mask >> 12, addrs[i + off + 1]);
-		} else {
-			/* brcl mask,off */
-			EMIT6_PCREL_RILC(0xc0040000,
-					 mask >> 12, addrs[i + off + 1]);
-		}
-		break;
+		/* lgfi %w1,imm (load sign extend imm) */
+		src_reg = REG_1;
+		EMIT6_IMM(0xc0010000, src_reg, imm);
+		goto branch_xu;
 branch_xs:
 		is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
 		if (!is_first_pass(jit) &&
-- 
2.25.4


  parent reply	other threads:[~2020-07-17 16:55 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 16:53 [PATCH 0/5] s390/bpf: fix lib/test_bpf.c failures Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 1/5] selftests: bpf: test_kmod.sh: fix running out of srctree Ilya Leoshkevich
2020-07-17 16:53 ` Ilya Leoshkevich [this message]
2020-07-17 22:23   ` [PATCH 2/5] s390/bpf: fix sign extension in branch_ku Seth Forshee
2020-07-17 16:53 ` [PATCH 3/5] s390/bpf: use brcl for jumping to exit_ip if necessary Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 4/5] s390/bpf: tolerate not converging code shrinking Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 5/5] s390/bpf: use bpf_skip() in bpf_jit_prologue() Ilya Leoshkevich
2020-07-21 18:17 ` [PATCH 0/5] s390/bpf: fix lib/test_bpf.c failures Alexei Starovoitov

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