Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B55CC05027 for ; Mon, 6 Feb 2023 14:18:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230465AbjBFOSd (ORCPT ); Mon, 6 Feb 2023 09:18:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37836 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230190AbjBFOSb (ORCPT ); Mon, 6 Feb 2023 09:18:31 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59A55271F for ; Mon, 6 Feb 2023 06:18:30 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EC60260F00 for ; Mon, 6 Feb 2023 14:18:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 85D84C433EF; Mon, 6 Feb 2023 14:18:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1675693109; bh=N0jlMsP1a2pFkwKypT6oJ/20U4sMLM/W0F/2lPeQtH8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=KyQCMI370m77ZFJVsLt4vh91v8swcCjpfKYfTyb4Tz8MzTaS5yF/MGnh8W93SoK/r LQ19aVaCKU7AKrAkrgEIi+an++7Z6vSqrEOgEgKgEleC6F/PnL/mkdrfflOBqiDXxh a6k1eNGlCTeJ1Rs20nxB3dh2MksWlPeqLZcNWs1sr5VN/8rQFor9DG7oUj0K4p5ry6 HN+S7wrC65E2nSHUiAnjBgOCLfjFhKi057H+NuW+DBgL1kjXGavol0C4pOGpfcXnlt iVoq209YXW1oMGRglGmrpplimHaqfFShhvW5uGk5hd3RNJin56keFDn60krgE5cdWg ATQ71xDejZ8xQ== Date: Mon, 6 Feb 2023 23:18:25 +0900 From: Masami Hiramatsu (Google) To: Nadav Amit Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, linux-kernel@vger.kernel.org, Nadav Amit , Masami Hiramatsu , Peter Zijlstra Subject: Re: [PATCH] x86/kprobes: Fix 1 byte conditional jump target Message-Id: <20230206231825.9997d73ded8497df9006585d@kernel.org> In-Reply-To: <20230204210807.3930-1-namit@vmware.com> References: <20230204210807.3930-1-namit@vmware.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 4 Feb 2023 21:08:07 +0000 Nadav Amit wrote: > From: Nadav Amit > > Commit 3bc753c06dd0 ("kbuild: treat char as always unsigned") broke > kprobes. Setting a probe-point on 1 byte conditional jump can cause the > kernel to crash, as the branch target is not sign extended. Oops, indeed! > > Fix by using s8 instead of char and use immediate.value instead of > immediate.bytes for consistency. Looks good to me. Thanks for finding this bug! Acked-by: Masami Hiramatsu (Google) Fixes: 3bc753c06dd0 ("kbuild: treat char as always unsigned") Thank you! > > Cc: Masami Hiramatsu (Google) > Cc: Peter Zijlstra > Signed-off-by: Nadav Amit > --- > arch/x86/kernel/kprobes/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index b36f3c367cb2..6a56d56b3817 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -625,7 +625,7 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn) > /* 1 byte conditional jump */ > p->ainsn.emulate_op = kprobe_emulate_jcc; > p->ainsn.jcc.type = opcode & 0xf; > - p->ainsn.rel32 = *(char *)insn->immediate.bytes; > + p->ainsn.rel32 = *(s8 *)&insn->immediate.value; > break; > case 0x0f: > opcode = insn->opcode.bytes[1]; > -- > 2.34.1 > -- Masami Hiramatsu (Google)