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Patch "arm64: bpf: fix mod-by-zero case" has been added to the 4.1-stable tree

PATCH [email protected] 1 participant 1 message Jan 27, 2016

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Stable branch BPF arm64 BPF JIT for arm64
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This is a note to let you know that I've just added the patch titled

arm64: bpf: fix mod-by-zero case

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-bpf-fix-mod-by-zero-case.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 14e589ff4aa3f28a5424e92b6495ecb8950080f7 Mon Sep 17 00:00:00 2001

From: Zi Shen Lim <[email protected]>
Date: Wed, 4 Nov 2015 20:43:59 -0800
Subject: arm64: bpf: fix mod-by-zero case

From: Zi Shen Lim <[email protected]>

commit 14e589ff4aa3f28a5424e92b6495ecb8950080f7 upstream.

Turns out in the case of modulo by zero in a BPF program:

	A = A % X;  (X == 0)

the expected behavior is to terminate with return value 0.

The bug in JIT is exposed by a new test case [1].

[1] https://lkml.org/lkml/2015/11/4/499

Signed-off-by Zi Shen Lim <[email protected]>
Reported-by Yang Shi <[email protected]>
Reported-by Xi Wang <[email protected]>
CC Alexei Starovoitov <[email protected]>
Fixes e54bcde3d69d ("arm64: eBPF JIT compiler")
Signed-off-by Catalin Marinas <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/arm64/net/bpf_jit_comp.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)
arch/arm64/net/bpf_jit_comp.c +13 -8
@@ -269,6 +269,8 @@ static int build_insn(const struct bpf_i
 		break;
 	case BPF_ALU | BPF_DIV | BPF_X:
 	case BPF_ALU64 | BPF_DIV | BPF_X:
+	case BPF_ALU | BPF_MOD | BPF_X:
+	case BPF_ALU64 | BPF_MOD | BPF_X:
 	{
 		const u8 r0 = bpf2a64[BPF_REG_0];
 

@@ -281,16 +283,19 @@ static int build_insn(const struct bpf_i
 		check_imm26(jmp_offset);
 		emit(A64_B(jmp_offset), ctx);
 		/* else */
-		emit(A64_UDIV(is64, dst, dst, src), ctx);
+		switch (BPF_OP(code)) {
+		case BPF_DIV:
+			emit(A64_UDIV(is64, dst, dst, src), ctx);
+			break;
+		case BPF_MOD:
+			ctx->tmp_used = 1;
+			emit(A64_UDIV(is64, tmp, dst, src), ctx);
+			emit(A64_MUL(is64, tmp, tmp, src), ctx);
+			emit(A64_SUB(is64, dst, dst, tmp), ctx);
+			break;
+		}
 		break;
 	}
-	case BPF_ALU | BPF_MOD | BPF_X:
-	case BPF_ALU64 | BPF_MOD | BPF_X:
-		ctx->tmp_used = 1;
-		emit(A64_UDIV(is64, tmp, dst, src), ctx);
-		emit(A64_MUL(is64, tmp, tmp, src), ctx);
-		emit(A64_SUB(is64, dst, dst, tmp), ctx);
-		break;
 	case BPF_ALU | BPF_LSH | BPF_X:
 	case BPF_ALU64 | BPF_LSH | BPF_X:
 		emit(A64_LSLV(is64, dst, dst, src), ctx);

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/arm64-bpf-fix-mod-by-zero-case.patch
queue-4.1/arm64-bpf-fix-div-by-zero-case.patch