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 38722C7EE23 for ; Tue, 23 May 2023 13:25:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233708AbjEWNZ4 (ORCPT ); Tue, 23 May 2023 09:25:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53080 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230130AbjEWNZx (ORCPT ); Tue, 23 May 2023 09:25:53 -0400 Received: from mail.ispras.ru (mail.ispras.ru [83.149.199.84]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C490BFF for ; Tue, 23 May 2023 06:25:48 -0700 (PDT) Received: from mail.ispras.ru (unknown [83.149.199.84]) by mail.ispras.ru (Postfix) with ESMTPSA id C32A140755F6; Tue, 23 May 2023 13:25:45 +0000 (UTC) DKIM-Filter: OpenDKIM Filter v2.11.0 mail.ispras.ru C32A140755F6 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ispras.ru; s=default; t=1684848345; bh=0iLXMfAG64un1bK4+l+r1HB734Vlmbk2PlPOZutpnzg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Ixefp+5MZcH+kctUKLe0AiWgkUNjiEgHLEXGQtRJysEMRDXjf+YAA55EOmQnCiF3S INbiWJ5fn2erFqwXBZultwEE+1oUW1BP/4jD/RfiDlvGJd8ezSn4dEd8wyoWphMMPY 5dVqQEQhqMUeZNqMNDA2hwVWKmD/epQY4xOX0GPw= MIME-Version: 1.0 Date: Tue, 23 May 2023 16:25:45 +0300 From: Alexey Izbyshev To: Catalin Marinas 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 In-Reply-To: References: <20230517150321.2890206-1-revest@chromium.org> <20230517150321.2890206-4-revest@chromium.org> <884d131bbc28ebfa0b729176e6415269@ispras.ru> <3c2e210b75bd56909322e8a3e5086d91@ispras.ru> User-Agent: Roundcube Webmail/1.4.4 Message-ID: X-Sender: izbyshev@ispras.ru Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). 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 Thanks, Alexey [1] https://lore.kernel.org/lkml/7c572622c0d8e283fc880fe3f4ffac27@ispras.ru//lkml/7c572622c0d8e283fc880fe3f4ffac27@ispras.ru > Any int passed to arg[2-5] would be converted by the compiler to an > unsigned long before being passed to the kernel. So I think the change > in this patch is harmless as the conversion is happening anyway. > > (well, unless I completely missed what the problem is)