From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED423C6778F for ; Wed, 25 Jul 2018 15:54:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEDBE204EC for ; Wed, 25 Jul 2018 15:54:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AEDBE204EC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729197AbeGYRGs (ORCPT ); Wed, 25 Jul 2018 13:06:48 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:41230 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728568AbeGYRGs (ORCPT ); Wed, 25 Jul 2018 13:06:48 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 29D9780D; Wed, 25 Jul 2018 08:54:32 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 59D8A3F575; Wed, 25 Jul 2018 08:54:30 -0700 (PDT) Date: Wed, 25 Jul 2018 16:54:27 +0100 From: Dave Martin To: Will Deacon Cc: linux-kernel@vger.kernel.org, arnd@arndb.de, oleg@redhat.com, linux@dominikbrodowski.net, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, steve.mcintyre@arm.com, linux-arm-kernel@lists.infradead.org, ebiederm@xmission.com Subject: Re: [PATCH 1/2] signal: Introduce COMPAT_SIGMINSTKSZ for use in compat_sys_sigaltstack Message-ID: <20180725155427.GR4240@e103592.cambridge.arm.com> References: <1532526312-26993-1-git-send-email-will.deacon@arm.com> <1532526312-26993-2-git-send-email-will.deacon@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1532526312-26993-2-git-send-email-will.deacon@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 25, 2018 at 02:45:11PM +0100, Will Deacon wrote: > The sigaltstack(2) system call fails with -ENOMEM if the new alternative > signal stack is found to be smaller than SIGMINSTKSZ. On architectures > such as arm64, where the native value for SIGMINSTKSZ is larger than > the compat value, this can result in an unexpected error being reported > to a compat task. See, for example: > > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=904385 > > This patch fixes the problem by extending do_sigaltstack to take the > minimum signal stack size as an additional parameter, allowing the > native and compat system call entry code to pass in their respective > values. COMPAT_SIGMINSTKSZ is just defined as SIGMINSTKSZ if it has not > been defined by the architecture. > > Cc: Arnd Bergmann > Cc: Dominik Brodowski > Cc: "Eric W. Biederman" > Cc: Andrew Morton > Cc: Al Viro > Cc: Oleg Nesterov > Reported-by: Steve McIntyre > Signed-off-by: Will Deacon > --- > include/linux/compat.h | 3 +++ > kernel/signal.c | 14 +++++++++----- > 2 files changed, 12 insertions(+), 5 deletions(-) > > diff --git a/include/linux/compat.h b/include/linux/compat.h > index c68acc47da57..47041c7fed28 100644 > --- a/include/linux/compat.h > +++ b/include/linux/compat.h > @@ -103,6 +103,9 @@ typedef struct compat_sigaltstack { > compat_size_t ss_size; > } compat_stack_t; > #endif > +#ifndef COMPAT_MINSIGSTKSZ > +#define COMPAT_MINSIGSTKSZ MINSIGSTKSZ > +#endif > > #define compat_jiffies_to_clock_t(x) \ > (((unsigned long)(x) * COMPAT_USER_HZ) / HZ) > diff --git a/kernel/signal.c b/kernel/signal.c > index 8d8a940422a8..41a5dd2df27d 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -3417,7 +3417,8 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact) > } > > static int > -do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp) > +do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp, > + size_t min_ss_size) > { > struct task_struct *t = current; > > @@ -3447,7 +3448,7 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp) > ss_size = 0; > ss_sp = NULL; > } else { > - if (unlikely(ss_size < MINSIGSTKSZ)) > + if (unlikely(ss_size < min_ss_size)) > return -ENOMEM; > } > > @@ -3465,7 +3466,8 @@ SYSCALL_DEFINE2(sigaltstack,const stack_t __user *,uss, stack_t __user *,uoss) > if (uss && copy_from_user(&new, uss, sizeof(stack_t))) > return -EFAULT; > err = do_sigaltstack(uss ? &new : NULL, uoss ? &old : NULL, > - current_user_stack_pointer()); > + current_user_stack_pointer(), > + MINSIGSTKSZ); > if (!err && uoss && copy_to_user(uoss, &old, sizeof(stack_t))) > err = -EFAULT; > return err; > @@ -3476,7 +3478,8 @@ int restore_altstack(const stack_t __user *uss) > stack_t new; > if (copy_from_user(&new, uss, sizeof(stack_t))) > return -EFAULT; > - (void)do_sigaltstack(&new, NULL, current_user_stack_pointer()); > + (void)do_sigaltstack(&new, NULL, current_user_stack_pointer(), > + MINSIGSTKSZ); Why can't this fail? If this fails here we silently go wrong, but... > /* squash all but EFAULT for now */ > return 0; > } > @@ -3510,7 +3513,8 @@ static int do_compat_sigaltstack(const compat_stack_t __user *uss_ptr, > uss.ss_size = uss32.ss_size; > } > ret = do_sigaltstack(uss_ptr ? &uss : NULL, &uoss, > - compat_user_stack_pointer()); > + compat_user_stack_pointer(), > + COMPAT_MINSIGSTKSZ); If this fails on arm64, we seem to SEGV (see compat_sys_rt_sigreturn()). This patch doesn't introduce this inconsistency, this might be a good opportunity to clean it up. Cheers ---Dave