Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753256AbcJRVfu (ORCPT ); Tue, 18 Oct 2016 17:35:50 -0400 Received: from mx2.suse.de ([195.135.220.15]:55086 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750770AbcJRVfn (ORCPT ); Tue, 18 Oct 2016 17:35:43 -0400 Date: Tue, 18 Oct 2016 23:35:41 +0200 From: "Luis R. Rodriguez" To: Arnd Bergmann Cc: Jiri Kosina , Linus Torvalds , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "Luis R. Rodriguez" , Boris Ostrovsky , Juergen Gross Subject: Re: [PATCH 22/28] x86: apm: avoid uninitialized data Message-ID: <20161018213541.GW8651@wotan.suse.de> References: <20161017220342.1627073-1-arnd@arndb.de> <20161017221650.1902729-3-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20161017221650.1902729-3-arnd@arndb.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2168 Lines: 58 On Tue, Oct 18, 2016 at 12:16:10AM +0200, Arnd Bergmann wrote: > apm_bios_call() can fail, and return a status in its argument > structure. If that status however is zero during a call from > apm_get_power_status(), we end up using data that may have > never been set, as reported by "gcc -Wmaybe-uninitialized": Userspace *may* already rely on this broken behavior for broken BIOSes which may leave the return value as 0, ignoring that, this change makes sense to me given that handling the error would be better than relying any possible invalid data. > arch/x86/kernel/apm_32.c: In function ‘apm’: > arch/x86/kernel/apm_32.c:1729:17: error: ‘bx’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > arch/x86/kernel/apm_32.c:1835:5: error: ‘cx’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > arch/x86/kernel/apm_32.c:1730:17: note: ‘cx’ was declared here > arch/x86/kernel/apm_32.c:1842:27: error: ‘dx’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > arch/x86/kernel/apm_32.c:1731:17: note: ‘dx’ was declared here > > This changes the function to return "APM_NO_ERROR" here, which > makes the code more robust to broken BIOS versions, and avoids > the warning. > > Cc: x86@kernel.org > Signed-off-by: Arnd Bergmann Reviewed-by: Luis R. Rodriguez Luis > --- > arch/x86/kernel/apm_32.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c > index c7364bd..51287cd 100644 > --- a/arch/x86/kernel/apm_32.c > +++ b/arch/x86/kernel/apm_32.c > @@ -1042,8 +1042,11 @@ static int apm_get_power_status(u_short *status, u_short *bat, u_short *life) > > if (apm_info.get_power_status_broken) > return APM_32_UNSUPPORTED; > - if (apm_bios_call(&call)) > + if (apm_bios_call(&call)) { > + if (!call.err) > + return APM_NO_ERROR; > return call.err; > + } > *status = call.ebx; > *bat = call.ecx; > if (apm_info.get_power_status_swabinminutes) { > -- > 2.9.0 > > -- Luis Rodriguez, SUSE LINUX GmbH Maxfeldstrasse 5; D-90409 Nuernberg