From patchwork Wed Nov 4 21:18:09 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Collingbourne X-Patchwork-Id: 11883269 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=-12.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 7B470C00A89 for ; Thu, 5 Nov 2020 05:11:58 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F20672083B for ; Thu, 5 Nov 2020 05:11:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="C0jUM5yW"; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="qx3uCJ8G"; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="VPeI7hVS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F20672083B Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:To:From:Subject:References:Mime-Version:Message-Id: In-Reply-To:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=85TUg91IDO9J4n60ws+fEK0svBeTRg3AknXxqCjrB7E=; b=C0jUM5yW2WuV16LBM6B8uHtLW f+QLI+ePEkoHV6cBvbJM++CnQgHx/7VP3udU6/nVZBn+76VJiQMzBVXG+SJ4KhPMPHD4u6Ax/L6AO H2vQVUJnGHVzTZsbH90KceRFHNMjoyQfZYLJsgXr+iUStRVvevFbIDia4JwMoZWNlZrhy8Z7IjjWe 8stxX5efznphaQipt5WNzh5WxltmCD8PypGh8wMUqDVl7+rsbBhBPUFOOsccmrAejh46iOhU5mpGE BlrUt0ppesmtTpDXG8+c+C+G0xJannXXIe9YtEEWhVXskbwBFlEVNhMk0YFy87i90dkg8TzmzanY/ 00K5v8Ugw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kaXX4-0006kl-2Z; Thu, 05 Nov 2020 05:09:58 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kaW7u-00016k-8i for linux-arm-kernel@merlin.infradead.org; Thu, 05 Nov 2020 03:39:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:Cc:To:From:Subject: References:Mime-Version:Message-Id:In-Reply-To:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=1F5n8xtS2dM5ch0WQR4OI0jZvv8gDSLIMGjbAJfRQFg=; b=qx3uCJ8GKO/x0GztDY+k4GnTGW dXitWuyYUycMehtO2vc61SRGzBTsv0HIcT5MAYfUKaXdmNuarlbPZtgKaFk28h7b8gKE9i/w/yVTU 0B6nr3sUoVzd+eMdG9H0wQn8JVLTr1yPwxPDtHOBXseYC5L90sj+DdsGC35YiElgJZJ4riDRruOjA DK14gyLujtJhbIgvPlCr3MQ8uQnFk9bz9l8O3qVDx1gfGXRJyTtlCnWeBlTZRDCcy5WNbpQWzR3Li w/g/gvuq9y1xa4kRwFtmN0SNPxOn7Vw0DWLCmjm9ePhYypPoSlKgA9Ev4IysBxkt0DitLQsBwzkFC d3DdDB0w==; Received: from mail-pg1-x54a.google.com ([2607:f8b0:4864:20::54a]) by casper.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kaQBq-0000pv-QO for linux-arm-kernel@lists.infradead.org; Wed, 04 Nov 2020 21:19:39 +0000 Received: by mail-pg1-x54a.google.com with SMTP id j13so14739302pgp.11 for ; Wed, 04 Nov 2020 13:19:33 -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=1F5n8xtS2dM5ch0WQR4OI0jZvv8gDSLIMGjbAJfRQFg=; b=VPeI7hVSTtcadpuYSXbsMJD0uZh0MTNOT604DbJ0REXA9KtSMpJXxnnvzlGmPNcjfc 3g4xEqnW9WskyHOBXMpp3RxPuq6LWfnw8kWb4N0qb7bLSkWnf2tdW1wZjvP9Vc8R0Eoy X3kKwZDLgfV71dUon6XGaCSZrWDfr18NvCVrlLXaIz+VCZf3AL6eF5/NtBv8Ub2Bjna1 QbvZRznDtO/LodA7h2+zj7mGdoHZknH/se8/HCQNEop+GG66u0q65jFGCWJFF28b95PI //ZoWTTUH6udZ/G3NDTywthSVZT+v9gmD+DpkMA/iqr360bkyRpEcfPpmiw28oVhihJi 3RKg== 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=1F5n8xtS2dM5ch0WQR4OI0jZvv8gDSLIMGjbAJfRQFg=; b=luVA97l+uSxnIepwEblk0uwQ5fOlknTJG5fIKx/CpKtaoMkulcykH18yclnQGpo+r4 XSt4zNK+yBntxz+kjE7s9lXgqslSj6rUwaIDiVq4fFP2B08k+grc/N+YhQdndpYj7QaN qxgsTiGUgdhXtS3nJlv+9SU+vuNJf23mPIBTl9N3+bt5GIF1o7xSKWw1ZwV8RRTz0RuF 8Py0Fhai33WZNUEp4nASDrYJVR1bQV1dJMBE7b72D/0c1Gho5ZR3xE0ZakJB3+ZNcP3m hqI1YUdeqjCJyk7vg0q+083QTS+jwcUVUG8KiaaULSAJpFQ3YNr6M1/Jwacblfoj4x1i JOiw== X-Gm-Message-State: AOAM531vboCD0zqZQ1WfS2DLOHQ8rjX4NIx7SEHIA2Z1FiYBrgt1ZrY5 5c7riAhelVBRkQjI+5J5SHST2J8= X-Google-Smtp-Source: ABdhPJxfFXRJAMUgdz1uktN8ikMzTi9fkdDEJI54Vm+4AUpSnekGYZn4MG1xizafJRvzrOq0L5Rb9AU= X-Received: from pcc-desktop.svl.corp.google.com ([2620:15c:2ce:0:7220:84ff:fe09:385a]) (user=pcc job=sendgmr) by 2002:a17:90b:46d7:: with SMTP id jx23mr6213173pjb.86.1604524710112; Wed, 04 Nov 2020 13:18:30 -0800 (PST) Date: Wed, 4 Nov 2020 13:18:09 -0800 In-Reply-To: Message-Id: <87501c1e71b5a6ed96bb9b540718b0752d4d6fed.1604523707.git.pcc@google.com> Mime-Version: 1.0 References: X-Mailer: git-send-email 2.29.1.341.ge80a0c044ae-goog Subject: [PATCH v14 6/8] 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" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201104_211935_326544_81B90D7F X-CRM114-Status: GOOD ( 17.94 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrey Konovalov , Helge Deller , Kevin Brodsky , linux-api@vger.kernel.org, David Spickett , Peter Collingbourne , Linux ARM , Richard Henderson Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 832b654dee8c..d18930aafbf4 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3964,6 +3964,12 @@ 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