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 DBC8BC7EE23 for ; Tue, 23 May 2023 14:11:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237164AbjEWOLb (ORCPT ); Tue, 23 May 2023 10:11:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237052AbjEWOLQ (ORCPT ); Tue, 23 May 2023 10:11:16 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F04D19B0 for ; Tue, 23 May 2023 07:10:22 -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 F11B061924 for ; Tue, 23 May 2023 14:10:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F2AFC433D2; Tue, 23 May 2023 14:10:01 +0000 (UTC) Date: Tue, 23 May 2023 15:09:58 +0100 From: Catalin Marinas To: Alexey Izbyshev Cc: David Hildenbrand , Florent Revest , 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, peterx@redhat.com, broonie@kernel.org, szabolcs.nagy@arm.com, kpsingh@kernel.org, gthelen@google.com, toiwoton@gmail.com Subject: Re: [PATCH v2 3/5] mm: Make PR_MDWE_REFUSE_EXEC_GAIN an unsigned long Message-ID: References: <20230517150321.2890206-1-revest@chromium.org> <20230517150321.2890206-4-revest@chromium.org> <884d131bbc28ebfa0b729176e6415269@ispras.ru> <3c2e210b75bd56909322e8a3e5086d91@ispras.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 23, 2023 at 04:25:45PM +0300, Alexey Izbyshev wrote: > On 2023-05-23 16:07, Catalin Marinas wrote: > > On Tue, May 23, 2023 at 11:12:37AM +0200, David Hildenbrand wrote: > > > Also, how is passing "0"s to e.g., PR_GET_THP_DISABLE reliable? We > > > need arg2 > > > -> arg5 to be 0. But wouldn't the following also just pass a 0 "int" ? > > > > > > prctl(PR_GET_THP_DISABLE, 0, 0, 0, 0) > > > > > > I'm easily confused by such (va_args) things, so sorry for the dummy > > > questions. > > > > Isn't the prctl() prototype in the user headers defined with the first > > argument as int while the rest as unsigned long? At least from the man > > page: > > > > int prctl(int option, unsigned long arg2, unsigned long arg3, > > unsigned long arg4, unsigned long arg5); > > > > So there are no va_args tricks (which confuse me as well). > > > I have explicitly mentioned the problem with man pages in my response to > David[1]. Quoting myself: > > > This stuff *is* confusing, and note that Linux man pages don't even tell > that prctl() is actually declared as a variadic function (and for > ptrace() this is mentioned only in the notes, but not in its signature). Ah, thanks for the clarification (I somehow missed your reply). > The reality: > > * glibc: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/sys/prctl.h;h=821aeefc1339b35210e8918ecfe9833ed2792626;hb=glibc-2.37#l42 > > * musl: > https://git.musl-libc.org/cgit/musl/tree/include/sys/prctl.h?h=v1.2.4#n180 > > Though there is a test in the kernel that does define its own prototype, > avoiding the issue: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/sched/cs_prctl_test.c?h=v6.3#n77 At least for glibc, it seems that there is a conversion to unsigned long: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/prctl.c#l28 unsigned long int arg2 = va_arg (arg, unsigned long int); (does va_arg expand to an actual cast?) If the libc passes a 32-bit to a kernel ABI that expects 64-bit, I think it's a user-space bug and not a kernel ABI issue. -- Catalin