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 43BF7C00144 for ; Mon, 1 Aug 2022 13:32:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230521AbiHANcR (ORCPT ); Mon, 1 Aug 2022 09:32:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229971AbiHANcR (ORCPT ); Mon, 1 Aug 2022 09:32:17 -0400 Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 262ED3DBF5; Mon, 1 Aug 2022 06:32:16 -0700 (PDT) Received: by mail-ed1-x52c.google.com with SMTP id f22so2741034edc.7; Mon, 01 Aug 2022 06:32:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=ZxYrCxuzFrawIOausSiSl14ADX47XgPrIEvhY9YR8N0=; b=FG40CLQaCqWW5WmzTFFQSiRNqPlRfCjRKug0ubumNYq7OCe2hzZ6dcawenMB3OH75x g+YgcH8BZajKnjbfx7vEKh42aZsK01e+lUq7FUDZdUCAV0vDrfCggkhK79DJjk0N7UPt CKPDp24FH9GgQ78TpOUPvHcK52VWswx5Wp5368LiBPBn/VaghUjpZCLkjY/w4sKsf6Bg 3xVRw4NnoPia1JPPkdr3NcN/RzpHMWRJxeNya71bE5XjASABarYpeM/AgU069YUaSJW9 +6Eb0VqjCl74TEGIzufXEpXGvEPotWAp3lnZC1w6o5b1NiC4k9yVZjBMnIleBfaaXQo6 DKRw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=ZxYrCxuzFrawIOausSiSl14ADX47XgPrIEvhY9YR8N0=; b=dAKdDcPL/hRXS02ywuQPBd6Hjpz4MgdbzMmML7fWx5hTB7vEGWytCkWzzEkUjQcj1P BTdAmlDUzR7fVa0RS+HK0o+XPRXsA6yhDLeZxxblTOFgQZNe35QUxs2FFgTGgcyVtg8y +auu+xbYf0oDtakYYLmnPs+inPbS/y5HH/Dz/SHMo7tvGWZ85TSpyYHAsUldCDdtfsxi zEyZumhslsbq/t+QHGVqoYqy/aKS0WAFUfh/e8UOxLHm4r6B/oO7udqzK24D388DXdNt 3U9Vu7aFDfcgu5vTrJiG5ynTfWQuy+/1cdAJyB33Iix3vtxoSwiHBpQjte5oddXf/dnn y85Q== X-Gm-Message-State: AJIora+h1+eZYxkFtw8QLFVC5PZ4rUujNyGvNrzRFEJJ8MnYnEVBxSGJ 446NFcTpr8FKZW+kjXa0rY8= X-Google-Smtp-Source: AGRyM1uoV5kr9uYFLy6H0i7TZWPOAEwEtFNpJ2kSfifyEQfER6jE35YeezQSQJn7eR0cvzR5blWSDg== X-Received: by 2002:a05:6402:1e88:b0:43c:e8d4:bf27 with SMTP id f8-20020a0564021e8800b0043ce8d4bf27mr15855237edf.401.1659360734629; Mon, 01 Aug 2022 06:32:14 -0700 (PDT) Received: from gmail.com (84-236-113-167.pool.digikabel.hu. [84.236.113.167]) by smtp.gmail.com with ESMTPSA id w7-20020aa7d287000000b0043bc19efc15sm6756395edq.28.2022.08.01.06.32.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Aug 2022 06:32:14 -0700 (PDT) Sender: Ingo Molnar Date: Mon, 1 Aug 2022 15:32:12 +0200 From: Ingo Molnar To: Mathieu Desnoyers Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Thomas Gleixner , "Paul E . McKenney" , Boqun Feng , "H . Peter Anvin" , Paul Turner , linux-api@vger.kernel.org, Peter Oskolkov Subject: Re: [PATCH 2/2] rseq: Kill process when unknown flags are encountered in ABI structures Message-ID: References: <20220622194617.1155957-1-mathieu.desnoyers@efficios.com> <20220622194617.1155957-2-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220622194617.1155957-2-mathieu.desnoyers@efficios.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org * Mathieu Desnoyers wrote: > rseq_abi()->flags and rseq_abi()->rseq_cs->flags 29 upper bits are > currently unused. > > The current behavior when those bits are set is to ignore them. This is > not an ideal behavior, because when future features will start using > those flags, if user-space fails to correctly validate that the kernel > indeed supports those flags (e.g. with a new sys_rseq flags bit) before > using them, it may incorrectly assume that the kernel will handle those > flags way when in fact those will be silently ignored on older kernels. > > Validating that unused flags bits are cleared will allow a smoother > transition when those flags will start to be used by allowing > applications to fail early, and obviously, when they attempt to use the > new flags on an older kernel that does not support them. > > Signed-off-by: Mathieu Desnoyers > --- > kernel/rseq.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index 81d7dc80787b..bda8175f8f99 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -176,7 +176,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) > u32 flags, event_mask; > int ret; > > - if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS)) > + if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS) || cs_flags) > return -EINVAL; > > /* Get thread flags. */ > @@ -184,7 +184,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) > if (ret) > return ret; > > - if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS)) > + if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS) || flags) > return -EINVAL; Just to make it clear: no existing libraries/tooling out there have learned to rely on the old ABI that ignored unset flags, right? Only then is this patch ABI-safe. Thanks, Ingo