linux-kernel - [PATCH] arm64: bpf: fix signedness bug in loading 64-bit immediate

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Date:	Fri,  8 May 2015 01:39:51 -0400
From:	Xi Wang <xi.wang@...il.com>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	linux-kernel@...r.kernel.org, Xi Wang <xi.wang@...il.com>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>
Subject: [PATCH] arm64: bpf: fix signedness bug in loading 64-bit immediate

Consider "(u64)insn1.imm << 32 | imm" in the arm64 JIT.  Since imm is
signed 32-bit, it is sign-extended to 64-bit, losing the high 32 bits.
The fix is to convert imm to u32 first and zero-extend it to u64.

Also extend test_bpf to catch this JIT bug; the interpreter is correct.

Before:
test_bpf: #58 load 64-bit immediate ret -1 != 1 FAIL (1 times)

After:
test_bpf: #58 load 64-bit immediate 74 PASS

Fixes: 30d3d94cc3d5 ("arm64: bpf: add 'load 64-bit immediate' instruction")
Cc: Zi Shen Lim <zlim.lnx@...il.com>
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Signed-off-by: Xi Wang <xi.wang@...il.com>
---
 arch/arm64/net/bpf_jit_comp.c | 2 +-
 lib/test_bpf.c                | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index edba042b2325..14cdc099fda0 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -487,7 +487,7 @@ emit_cond_jmp:
 			return -EINVAL;
 		}
 
-		imm64 = (u64)insn1.imm << 32 | imm;
+		imm64 = ((u64)(u32)insn1.imm) << 32 | (u64)(u32)imm;
 		emit_a64_mov_i64(dst, imm64, ctx);
 
 		return 1;
diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 80d78c51f65f..9f6849891b5f 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -1755,7 +1755,8 @@ static struct bpf_test tests[] = {
 			BPF_EXIT_INSN(),
 			BPF_JMP_IMM(BPF_JEQ, R3, 0x1234, 1),
 			BPF_EXIT_INSN(),
-			BPF_ALU64_IMM(BPF_MOV, R0, 1),
+			BPF_LD_IMM64(R0, 0x1ffffffffLL),
+			BPF_ALU64_IMM(BPF_RSH, R0, 32), /* R0 = 1 */
 			BPF_EXIT_INSN(),
 		},
 		INTERNAL,
-- 
1.9.1

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