From patchwork Sat Oct 17 00:12:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Collingbourne X-Patchwork-Id: 11842469 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=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 73AD5C43457 for ; Sat, 17 Oct 2020 00:14:57 +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 03D6922227 for ; Sat, 17 Oct 2020 00:14:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="cuq6xnnq"; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="IdbWwjq/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 03D6922227 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=9+EfYL+hm52HxU8TEQ+OExpHrKtDtonY69au2DuSokg=; b=cuq6xnnqEjiafaaTF6gujE7xs 4vwvUrVJMtoP/3TtVU9j+J4+mLmyW7AaNg/IgXCEk5wVSfll5qQcBlf8PrgyuHXIR5hXiXy7YJHc8 FCvLRXV83qAjmzni876KX8LI9QXZ+8f28ARMScLLDiYDHBCqqjik+dq+gJtr4dOWXMRivpb/cfchN t19um37mKM5d5FOem1wkSk3vPrJIbGjOzXlSDtqA6b8PfaxjqQSHhZp4//McdB/fuQfQTIkMtGtkw ueUdpkZSxyWES/Bzql3QJ8Rt6kLzZ1C7STaMAQnW0lr6KNJjlX+RXPKG4wzyWVTzH1OGsxrbS/jK/ RKT2uNJig==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kTZqP-0001zr-9L; Sat, 17 Oct 2020 00:13:09 +0000 Received: from mail-qt1-x849.google.com ([2607:f8b0:4864:20::849]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kTZqE-0001x8-GG for linux-arm-kernel@lists.infradead.org; Sat, 17 Oct 2020 00:13:00 +0000 Received: by mail-qt1-x849.google.com with SMTP id o25so2407242qtt.3 for ; Fri, 16 Oct 2020 17:12:55 -0700 (PDT) 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=beJYRcTSMXl+ssB1hZRLQHWjWaa0LSzrjyL4rY4lfCE=; b=IdbWwjq/b+TLNtozI5kF+btUmTLlcbzVYXEGi1AU7DQGBpTF9aUlKXoyMLkzHkNYVx zF15uNRB5iKTJMqlEfG/VHAhK8M7AfhiIbi9Jj6ada9NwjlQqiU2WpSwg1hwShMhSSdX QN/Y7I3sqFvccG9a91KgIk1+oLceZh4SOTWzygKmHTta8SsCwGl6MOHwgsdNUkjKvbr4 dgrtJ30VpDPdGq1LFmvKGkQob5Aj12dxZpIr00Gqy1CvU8nNVae8FN7Y83M3bwxBoeuC kAomeqgPWXk/Pqadyt1O7ld1Fwvuhp5lcb0xs6sH3iymOp2JGVlPmueooCh6G24SG0q2 KdbA== 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=beJYRcTSMXl+ssB1hZRLQHWjWaa0LSzrjyL4rY4lfCE=; b=OFmEETdfm6cMvnK23qtF9aBdXH9vHDdEZWu3yx+rKps0zgQTtc/1u3ZGm7YNhf+RzN cDEB0SgDUhN1rqN1bYquyjjG1uMcWj89X64O+pnWzp7tFP8yIZ5o4hTyWuc/U2gRPBeE 4lRosJ9qSin46VzBoJWZdgFrKyUwdEKAj6dcScGKw+iJeM51RkDaXBs2f20AFaaE1V/U YR1mG3hc6V54CSPc2cvjEffpymCzefC7nB2PHvaW8X5kjpk2C8ESXAyBhhWlARFI9JdE 1I2MWLlDI6gQ6EDqWRlBDMk8XTuPwt9D3gUrm3uP6e+JvxgAqq5RPT+PzIRF+6uCPpNR 4g9Q== X-Gm-Message-State: AOAM531NXtNbyQq7/niGZ3e1/QUam7P4E2VtqtFu7KX0mAfESWfXMuVE Xiq9gQ6ycNK6qP3rrnjjDR62lNQ= X-Google-Smtp-Source: ABdhPJyzLwra6WILfeSqbZO3wb7k45mAfs3gB0fAOYaCDrkAeUSkn5dFszU06PBpEUlPQCRTQ9Yf86c= X-Received: from pcc-desktop.svl.corp.google.com ([2620:15c:2ce:0:7220:84ff:fe09:385a]) (user=pcc job=sendgmr) by 2002:a0c:aa98:: with SMTP id f24mr6581581qvb.62.1602893574439; Fri, 16 Oct 2020 17:12:54 -0700 (PDT) Date: Fri, 16 Oct 2020 17:12:30 -0700 In-Reply-To: Message-Id: Mime-Version: 1.0 References: X-Mailer: git-send-email 2.29.0.rc1.297.gfa9743e501-goog Subject: [PATCH v12 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" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201016_201258_578132_8A4BC276 X-CRM114-Status: GOOD ( 16.97 ) 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 2ef8c238679e..018c19f6cf66 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3984,6 +3984,12 @@ 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