linux-kernel - [PATCH 4.4 01/23] s390/bpf: Fix optimizing out zero-extensions

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Message-Id: <20210924124327.869013869@linuxfoundation.org>
Date:   Fri, 24 Sep 2021 14:43:42 +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,
        Johan Almbladh <johan.almbladh@...finetworks.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: [PATCH 4.4 01/23] s390/bpf: Fix optimizing out zero-extensions

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

commit db7bee653859ef7179be933e7d1384644f795f26 upstream.

Currently the JIT completely removes things like `reg32 += 0`,
however, the BPF_ALU semantics requires the target register to be
zero-extended in such cases.

Fix by optimizing out only the arithmetic operation, but not the
subsequent zero-extension.

Reported-by: Johan Almbladh <johan.almbladh@...finetworks.com>
Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
Reviewed-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/s390/net/bpf_jit_comp.c |   50 ++++++++++++++++++++++---------------------
 1 file changed, 26 insertions(+), 24 deletions(-)

--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -596,10 +596,10 @@ static noinline int bpf_jit_insn(struct
 		EMIT4(0xb9080000, dst_reg, src_reg);
 		break;
 	case BPF_ALU | BPF_ADD | BPF_K: /* dst = (u32) dst + (u32) imm */
-		if (!imm)
-			break;
-		/* alfi %dst,imm */
-		EMIT6_IMM(0xc20b0000, dst_reg, imm);
+		if (imm != 0) {
+			/* alfi %dst,imm */
+			EMIT6_IMM(0xc20b0000, dst_reg, imm);
+		}
 		EMIT_ZERO(dst_reg);
 		break;
 	case BPF_ALU64 | BPF_ADD | BPF_K: /* dst = dst + imm */
@@ -621,10 +621,10 @@ static noinline int bpf_jit_insn(struct
 		EMIT4(0xb9090000, dst_reg, src_reg);
 		break;
 	case BPF_ALU | BPF_SUB | BPF_K: /* dst = (u32) dst - (u32) imm */
-		if (!imm)
-			break;
-		/* alfi %dst,-imm */
-		EMIT6_IMM(0xc20b0000, dst_reg, -imm);
+		if (imm != 0) {
+			/* alfi %dst,-imm */
+			EMIT6_IMM(0xc20b0000, dst_reg, -imm);
+		}
 		EMIT_ZERO(dst_reg);
 		break;
 	case BPF_ALU64 | BPF_SUB | BPF_K: /* dst = dst - imm */
@@ -651,10 +651,10 @@ static noinline int bpf_jit_insn(struct
 		EMIT4(0xb90c0000, dst_reg, src_reg);
 		break;
 	case BPF_ALU | BPF_MUL | BPF_K: /* dst = (u32) dst * (u32) imm */
-		if (imm == 1)
-			break;
-		/* msfi %r5,imm */
-		EMIT6_IMM(0xc2010000, dst_reg, imm);
+		if (imm != 1) {
+			/* msfi %r5,imm */
+			EMIT6_IMM(0xc2010000, dst_reg, imm);
+		}
 		EMIT_ZERO(dst_reg);
 		break;
 	case BPF_ALU64 | BPF_MUL | BPF_K: /* dst = dst * imm */
@@ -715,6 +715,8 @@ static noinline int bpf_jit_insn(struct
 			if (BPF_OP(insn->code) == BPF_MOD)
 				/* lhgi %dst,0 */
 				EMIT4_IMM(0xa7090000, dst_reg, 0);
+			else
+				EMIT_ZERO(dst_reg);
 			break;
 		}
 		/* lhi %w0,0 */
@@ -807,10 +809,10 @@ static noinline int bpf_jit_insn(struct
 		EMIT4(0xb9820000, dst_reg, src_reg);
 		break;
 	case BPF_ALU | BPF_XOR | BPF_K: /* dst = (u32) dst ^ (u32) imm */
-		if (!imm)
-			break;
-		/* xilf %dst,imm */
-		EMIT6_IMM(0xc0070000, dst_reg, imm);
+		if (imm != 0) {
+			/* xilf %dst,imm */
+			EMIT6_IMM(0xc0070000, dst_reg, imm);
+		}
 		EMIT_ZERO(dst_reg);
 		break;
 	case BPF_ALU64 | BPF_XOR | BPF_K: /* dst = dst ^ imm */
@@ -831,10 +833,10 @@ static noinline int bpf_jit_insn(struct
 		EMIT6_DISP_LH(0xeb000000, 0x000d, dst_reg, dst_reg, src_reg, 0);
 		break;
 	case BPF_ALU | BPF_LSH | BPF_K: /* dst = (u32) dst << (u32) imm */
-		if (imm == 0)
-			break;
-		/* sll %dst,imm(%r0) */
-		EMIT4_DISP(0x89000000, dst_reg, REG_0, imm);
+		if (imm != 0) {
+			/* sll %dst,imm(%r0) */
+			EMIT4_DISP(0x89000000, dst_reg, REG_0, imm);
+		}
 		EMIT_ZERO(dst_reg);
 		break;
 	case BPF_ALU64 | BPF_LSH | BPF_K: /* dst = dst << imm */
@@ -856,10 +858,10 @@ static noinline int bpf_jit_insn(struct
 		EMIT6_DISP_LH(0xeb000000, 0x000c, dst_reg, dst_reg, src_reg, 0);
 		break;
 	case BPF_ALU | BPF_RSH | BPF_K: /* dst = (u32) dst >> (u32) imm */
-		if (imm == 0)
-			break;
-		/* srl %dst,imm(%r0) */
-		EMIT4_DISP(0x88000000, dst_reg, REG_0, imm);
+		if (imm != 0) {
+			/* srl %dst,imm(%r0) */
+			EMIT4_DISP(0x88000000, dst_reg, REG_0, imm);
+		}
 		EMIT_ZERO(dst_reg);
 		break;
 	case BPF_ALU64 | BPF_RSH | BPF_K: /* dst = dst >> imm */