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=-20.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 587F3C388F7 for ; Tue, 3 Nov 2020 04:10:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB07F2224E for ; Tue, 3 Nov 2020 04:10:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="hFAEBQgh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725982AbgKCEKP (ORCPT ); Mon, 2 Nov 2020 23:10:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35646 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725940AbgKCEKP (ORCPT ); Mon, 2 Nov 2020 23:10:15 -0500 Received: from mail-qt1-x84a.google.com (mail-qt1-x84a.google.com [IPv6:2607:f8b0:4864:20::84a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8B3BC0617A6 for ; Mon, 2 Nov 2020 20:10:13 -0800 (PST) Received: by mail-qt1-x84a.google.com with SMTP id c2so3005670qtx.3 for ; Mon, 02 Nov 2020 20:10:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=kxh8h3N2DC9f05BY16jRtsQux5LoEptNxLPFbLaVubI=; b=hFAEBQghSZm3DrkgGFeB6eSjBetEddg9g+LwnvX75dYJES+T/0yW2dl8pXaN/dN2Ux GY5mOyL02G1nWaVDCa8dI6dvcXOjeER9QvxSM8Lgpr/YHNcUkhLZlWFpke3VgHxnoll1 zToWEbjYJe79OOfgesLRKhtQxGfPbbiUQ3ZTSU3GHCqsURhJTJbgoxL3/ewZ7sFdXOi6 fldOAD92YJVQfI7pc0byytqxSzHQPtiDDmochrNe4EtpSUDRCvYx0UACGhGJFOBl8IEU zNNvZ+D+SjmfRkLZSFkOBVy2LxRr1TvXZcQOhaR9xnAaFzW6kgt2yiK2rplHYcR5OX6f Ajtw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=kxh8h3N2DC9f05BY16jRtsQux5LoEptNxLPFbLaVubI=; b=e/2lQSlIWiAVwRfJZbQfaHNkXhJwRHzKWwpV3Fm9fixv6wQl9qCnFBRhUsvWyCDNcG e9vghV4u+KC0vVUxnsQianTurAD0wP1MMDkjn79cRTqu63h/xyCSxej9SnFab4iw+CDr qWGOLWtFqdLespIiTvqjkT/PYqYjnFM09NR4hqjBeesq5zxbu1XRTS4QOdINr1qiJ6CV y9t+G01zQfTGciPuTepB2/l7SBHX9Fhne4DFScJvH6m7yTtsACAJ4T9v2ion3O8WoCTi 5Sqxci0TfrSjOJbDxoxB5TFfQv4Ce8zic87WZQKwYWSt6dEKCaSvguisTHh2zPwUK27U tXXQ== X-Gm-Message-State: AOAM530DCUqWPmkSOUGAhDCZ3U8dg73BAra1JG3cqx+20A0T1tmVtc7U sKmf/1k1jKUlRftM9uKkhIyH3QQ= X-Google-Smtp-Source: ABdhPJxDs2ct5LqoAJ8mGfvMmTa0bm63rH+4VBhrcMeDsQKIdobEezYvI3XoFYwGyX0lK6GSTaugJyQ= Sender: "pcc via sendgmr" X-Received: from pcc-desktop.svl.corp.google.com ([2620:15c:2ce:0:7220:84ff:fe09:385a]) (user=pcc job=sendgmr) by 2002:a05:6214:192d:: with SMTP id es13mr23963347qvb.27.1604376613013; Mon, 02 Nov 2020 20:10:13 -0800 (PST) Date: Mon, 2 Nov 2020 20:09:41 -0800 In-Reply-To: Message-Id: <832bc45b5636cdb40e079fbfacfed5650749c07a.1604376407.git.pcc@google.com> Mime-Version: 1.0 References: X-Mailer: git-send-email 2.29.1.341.ge80a0c044ae-goog Subject: [PATCH v13 5/8] signal: define the SA_UNSUPPORTED bit in sa_flags From: Peter Collingbourne To: Catalin Marinas , Evgenii Stepanov , Kostya Serebryany , Vincenzo Frascino , Dave Martin , Will Deacon , Oleg Nesterov , "Eric W. Biederman" , "James E.J. Bottomley" Cc: Peter Collingbourne , Linux ARM , Kevin Brodsky , Andrey Konovalov , Richard Henderson , linux-api@vger.kernel.org, Helge Deller , David Spickett Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Define a sa_flags bit, SA_UNSUPPORTED, which will never be supported in the uapi. The purpose of this flag bit is to allow userspace to distinguish an old kernel that does not clear unknown sa_flags bits from a kernel that supports every flag bit. In other words, if userspace does something like: act.sa_flags |= SA_UNSUPPORTED; sigaction(SIGSEGV, &act, 0); sigaction(SIGSEGV, 0, &oldact); and finds that SA_UNSUPPORTED remains set in oldact.sa_flags, it means that the kernel cannot be trusted to have cleared unknown flag bits from sa_flags, so no assumptions about flag bit support can be made. Signed-off-by: Peter Collingbourne Reviewed-by: Dave Martin Link: https://linux-review.googlesource.com/id/Ic2501ad150a3a79c1cf27fb8c99be342e9dffbcb --- v11: - clarify the commit message include/uapi/asm-generic/signal-defs.h | 7 +++++++ kernel/signal.c | 6 ++++++ 2 files changed, 13 insertions(+) diff --git a/include/uapi/asm-generic/signal-defs.h b/include/uapi/asm-generic/signal-defs.h index 493953fe319b..0126ebda4d31 100644 --- a/include/uapi/asm-generic/signal-defs.h +++ b/include/uapi/asm-generic/signal-defs.h @@ -14,6 +14,12 @@ * SA_RESTART flag to get restarting signals (which were the default long ago) * SA_NODEFER prevents the current signal from being masked in the handler. * SA_RESETHAND clears the handler when the signal is delivered. + * SA_UNSUPPORTED is a flag bit that will never be supported. Kernels from + * before the introduction of SA_UNSUPPORTED did not clear unknown bits from + * sa_flags when read using the oldact argument to sigaction and rt_sigaction, + * so this bit allows flag bit support to be detected from userspace while + * allowing an old kernel to be distinguished from a kernel that supports every + * flag bit. * * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single * Unix names RESETHAND and NODEFER respectively. @@ -42,6 +48,7 @@ #ifndef SA_RESETHAND #define SA_RESETHAND 0x80000000 #endif +#define SA_UNSUPPORTED 0x00000400 #define SA_NOMASK SA_NODEFER #define SA_ONESHOT SA_RESETHAND diff --git a/kernel/signal.c b/kernel/signal.c index 8f5bd12ee41b..8f34819e80de 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3985,6 +3985,12 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact) if (oact) *oact = *k; + /* + * Make sure that we never accidentally claim to support SA_UNSUPPORTED, + * e.g. by having an architecture use the bit in their uapi. + */ + BUILD_BUG_ON(UAPI_SA_FLAGS & SA_UNSUPPORTED); + /* * Clear unknown flag bits in order to allow userspace to detect missing * support for flag bits and to allow the kernel to use non-uapi bits -- 2.29.1.341.ge80a0c044ae-goog