linux-kernel - [PATCH 5.8 274/464] s390/bpf: Fix sign extension in branch

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Date:   Mon, 17 Aug 2020 17:13:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Seth Forshee <seth.forshee@...onical.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.8 274/464] s390/bpf: Fix sign extension in branch_ku

From: Ilya Leoshkevich <iii@...ux.ibm.com>

[ Upstream commit 7477d43be5b1448bc0d4c85cb185a0144cc080e1 ]

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@...onical.com>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Tested-by: Seth Forshee <seth.forshee@...onical.com>
Link: https://lore.kernel.org/bpf/20200717165326.6786-3-iii@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 f4242b894cf28..6b3d612948fba 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1417,21 +1417,10 @@ 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) &&
-- 
2.25.1