Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752405AbbEHIjF (ORCPT ); Fri, 8 May 2015 04:39:05 -0400 Received: from foss.arm.com ([217.140.101.70]:52188 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750968AbbEHIjD (ORCPT ); Fri, 8 May 2015 04:39:03 -0400 Date: Fri, 8 May 2015 09:38:57 +0100 From: Will Deacon To: Xi Wang Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Zi Shen Lim , Alexei Starovoitov , Catalin Marinas Subject: Re: [PATCH] arm64: bpf: fix signedness bug in loading 64-bit immediate Message-ID: <20150508083856.GA2125@arm.com> References: <1431063591-16668-1-git-send-email-xi.wang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1431063591-16668-1-git-send-email-xi.wang@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2278 Lines: 63 On Fri, May 08, 2015 at 06:39:51AM +0100, Xi Wang wrote: > 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 > Cc: Alexei Starovoitov > Cc: Catalin Marinas > Cc: Will Deacon > Signed-off-by: Xi Wang > --- > 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; This seems a bit convoluted to me. Don't you just need to add a (u32) cast to imm and that's it? The (u64)(u32) looks redundant. > 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(), This hunk should probably be a separate patch, unless you get Alexei's ack for me to take it via the arm64 tree too. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/