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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBFB0C7EE26 for ; Tue, 23 May 2023 16:36:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237666AbjEWQgV (ORCPT ); Tue, 23 May 2023 12:36:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235582AbjEWQgR (ORCPT ); Tue, 23 May 2023 12:36:17 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C5A8CE4B for ; Tue, 23 May 2023 09:36:07 -0700 (PDT) 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 4B5B863463 for ; Tue, 23 May 2023 16:36:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CDD67C433EF; Tue, 23 May 2023 16:36:03 +0000 (UTC) Date: Tue, 23 May 2023 17:36:00 +0100 From: Catalin Marinas To: Florent Revest Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, anshuman.khandual@arm.com, joey.gouly@arm.com, mhocko@suse.com, keescook@chromium.org, david@redhat.com, peterx@redhat.com, izbyshev@ispras.ru, broonie@kernel.org, szabolcs.nagy@arm.com, kpsingh@kernel.org, gthelen@google.com, toiwoton@gmail.com Subject: Re: [PATCH v2 4/5] mm: Add a NO_INHERIT flag to the PR_SET_MDWE prctl Message-ID: References: <20230517150321.2890206-1-revest@chromium.org> <20230517150321.2890206-5-revest@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230517150321.2890206-5-revest@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 17, 2023 at 05:03:20PM +0200, Florent Revest wrote: > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index 0ee96ea7a0e9..11f5e3dacb4e 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -91,4 +91,14 @@ static inline int get_dumpable(struct mm_struct *mm) > MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK) > > #define MMF_VM_MERGE_ANY 29 > +#define MMF_HAS_MDWE_NO_INHERIT 30 > + > +#define MMF_INIT_FLAGS(flags) ({ \ > + unsigned long new_flags = flags; \ > + if (new_flags & (1UL << MMF_HAS_MDWE_NO_INHERIT)) \ > + new_flags &= ~((1UL << MMF_HAS_MDWE) | \ > + (1UL << MMF_HAS_MDWE_NO_INHERIT)); \ > + new_flags & MMF_INIT_MASK; \ > +}) A function is better indeed, not sure who came up with this macro idea ;). > diff --git a/kernel/sys.c b/kernel/sys.c > index 339fee3eff6a..320eae3b12ab 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2368,9 +2368,25 @@ static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3, > if (arg3 || arg4 || arg5) > return -EINVAL; > > - if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN)) > + if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT)) > return -EINVAL; > > + /* NO_INHERIT only makes sense with REFUSE_EXEC_GAIN */ > + if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN)) > + return -EINVAL; > + > + /* Can't gain NO_INHERIT from !NO_INHERIT */ > + if (bits & PR_MDWE_NO_INHERIT && > + test_bit(MMF_HAS_MDWE, ¤t->mm->flags) && > + !test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags)) > + return -EPERM; > + > + if (bits & PR_MDWE_NO_INHERIT) > + set_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags); > + else if (test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags) > + && !(bits & PR_MDWE_REFUSE_EXEC_GAIN)) > + return -EPERM; /* Cannot unset the flag */ Is this about not unsetting the MMF_HAS_MDWE bit? We already have a check further down that covers this case. Related to this, do we want to allow unsetting MMF_HAS_MDWE_NO_INHERIT? It looks like it can't be unset but no error either. The above check, IIUC, looks more like ensuring we don't clear MMF_HAS_MDWE. Maybe we should tighten the logic here a bit and not allow any changes after the initial flag setting: current->mm->flags == 0, we allow: bits == 0 or bits == PR_MDWE_REFUSE_EXEC_GAIN or bits == PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT current->mm->flags != 0 (some bits were set), we only allow the exactly the same bit combination or -EPERM. So basically build the flags based on the PR_* input bits and compare them with current->mm->flags when not 0, return -EPERM if different. I think this preserves the ABI as we only have a single bit currently and hopefully makes the logic here easier to parse. > + > if (bits & PR_MDWE_REFUSE_EXEC_GAIN) > set_bit(MMF_HAS_MDWE, ¤t->mm->flags); > else if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags)) > @@ -2385,8 +2401,10 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3, > if (arg2 || arg3 || arg4 || arg5) > return -EINVAL; > > - return test_bit(MMF_HAS_MDWE, ¤t->mm->flags) ? > - PR_MDWE_REFUSE_EXEC_GAIN : 0; > + return (test_bit(MMF_HAS_MDWE, ¤t->mm->flags) ? > + PR_MDWE_REFUSE_EXEC_GAIN : 0) | > + (test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->mm->flags) ? > + PR_MDWE_NO_INHERIT : 0); > } Just personal preference, use explicit 'if' blocks and add bits to a local variable variable than multiple ternary operators. -- Catalin