From patchwork Sat Aug 22 05:10:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Collingbourne X-Patchwork-Id: 11730897 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E52D116B1 for ; Sat, 22 Aug 2020 05:10:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C8E212072D for ; Sat, 22 Aug 2020 05:10:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="DWyIkqyE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725922AbgHVFKf (ORCPT ); Sat, 22 Aug 2020 01:10:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725811AbgHVFKd (ORCPT ); Sat, 22 Aug 2020 01:10:33 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A45BC061573 for ; Fri, 21 Aug 2020 22:10:33 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id l67so4375265ybb.7 for ; Fri, 21 Aug 2020 22:10:33 -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=KrdxAilGBmE923YVVL9prklmvfKq2p4HPDeQrjFjEyM=; b=DWyIkqyEklyjgdoBNglLonZww9+p8LBWbdFnAHzb1tsVAn+VYTq7EiqnIgzZAw38L1 x+RKzjf2B9U3JCCQdu9SizqS7GzsEGuTffaXkT3HvtIFmAxS4VFwSscmssRvpQxJR62g c8NtKxoEeVNfQ3odGcYBxD/do7YOtX8a3ndoIeJPKVNTyAH5DZYUkSV8cgg0jVhkCzSc 2lLWhLseI1mlJvR8XsfUwhNR9oB48aohVvETZ6qkpaVPAzzd9sPxt/8aJwEIWkbeQyRr nBD7U87YRdxXd0DCO+H1YdCOwWQ9FgHUsYpobD/UqYiW0EHkIqPf2S/IZRfy8KpGKNGe ud9A== 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=KrdxAilGBmE923YVVL9prklmvfKq2p4HPDeQrjFjEyM=; b=A2BFyVFsD0PYUj/jWFQKA65zvy6NznSMuahWLFe9wHAVVAWRy3VoXK4ah1RCnungve n3/JrXH2WsRqqtcrY9rISwEiDmhIOM+00sHMRYylwUHKEzFngHM87O8YsaZQrYn7QVVl 3hvNJdNDBd/aSwuT8wpGl2+CcQDQ3dZe08XgAtSJE7909nN+LF4GwU0dB/RRXksAtdXO eU0pLgozLPiCfqEmEAEZZc1+kob5ujv/b4ep/u1wg/fbPKgQHbTpDRls0urADScYHs61 4zsWDnbdd9wAYSSmaAJHS6bc8jzY8XOm5tJe/rjfZNhNURGnVi11BAyl6KJOViJZX5hm t7tQ== X-Gm-Message-State: AOAM533hszq3kGCWDj3mXNkCeMqTOFCWZNNud606iYj/q4bojKH0w5Nf ABUSyTD4f2drEB40g2D11VHvtEQ= X-Google-Smtp-Source: ABdhPJwf5XbobwL1l/mHkrk+/iWLsQrxUpPJ7TZdQV9SNtzqlrADocDLwSXNXUq6r5XgT8VU7oAYSyw= X-Received: from pcc-desktop.svl.corp.google.com ([2620:15c:2ce:0:7220:84ff:fe09:385a]) (user=pcc job=sendgmr) by 2002:a25:2451:: with SMTP id k78mr8388338ybk.335.1598073032784; Fri, 21 Aug 2020 22:10:32 -0700 (PDT) Date: Fri, 21 Aug 2020 22:10:13 -0700 In-Reply-To: Message-Id: <868b8a89e4050d3f2d079bf28a18786e92b9c680.1598072840.git.pcc@google.com> Mime-Version: 1.0 References: X-Mailer: git-send-email 2.28.0.297.g1956fa8f8d-goog Subject: [PATCH v10 3/7] signal: clear non-uapi flag bits when passing/returning 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-parisc@vger.kernel.org, David Spickett Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org Previously we were not clearing non-uapi flag bits in sigaction.sa_flags when storing the userspace-provided sa_flags or when returning them via oldact. Start doing so. This allows userspace to detect missing support for flag bits and allows the kernel to use non-uapi bits internally, as we are already doing in arch/x86 for two flag bits. Now that this change is in place, we no longer need the code in arch/x86 that was hiding these bits from userspace, so remove it. This is technically a userspace-visible behavior change for sigaction, as the unknown bits returned via oldact.sa_flags are no longer set. However, we are free to define the behavior for unknown bits exactly because their behavior is currently undefined, so for now we can define the meaning of each of them to be "clear the bit in oldact.sa_flags unless the bit becomes known in the future". Furthermore, this behavior is consistent with OpenBSD [1], illumos [2] and XNU [3] (FreeBSD [4] and NetBSD [5] fail the syscall if unknown bits are set). So there is some precedent for this behavior in other kernels, and in particular in XNU, which is probably the most popular kernel among those that I looked at, which means that this change is less likely to be a compatibility issue. Link: [1] https://github.com/openbsd/src/blob/f634a6a4b5bf832e9c1de77f7894ae2625e74484/sys/kern/kern_sig.c#L278 Link: [2] https://github.com/illumos/illumos-gate/blob/76f19f5fdc974fe5be5c82a556e43a4df93f1de1/usr/src/uts/common/syscall/sigaction.c#L86 Link: [3] https://github.com/apple/darwin-xnu/blob/a449c6a3b8014d9406c2ddbdc81795da24aa7443/bsd/kern/kern_sig.c#L480 Link: [4] https://github.com/freebsd/freebsd/blob/eded70c37057857c6e23fae51f86b8f8f43cd2d0/sys/kern/kern_sig.c#L699 Link: [5] https://github.com/NetBSD/src/blob/3365779becdcedfca206091a645a0e8e22b2946e/sys/kern/sys_sig.c#L473 Signed-off-by: Peter Collingbourne --- View this change in Gerrit: https://linux-review.googlesource.com/q/I35aab6f5be932505d90f3b3450c083b4db1eca86 v10: - rename SA_UAPI_FLAGS -> UAPI_SA_FLAGS - refactor how we define it to avoid mentioning flags more than once arch/arm/include/asm/signal.h | 2 ++ arch/parisc/include/asm/signal.h | 2 ++ arch/x86/kernel/signal_compat.c | 7 ------- include/linux/signal_types.h | 12 ++++++++++++ kernel/signal.c | 10 ++++++++++ 5 files changed, 26 insertions(+), 7 deletions(-) diff --git a/arch/arm/include/asm/signal.h b/arch/arm/include/asm/signal.h index 65530a042009..430be7774402 100644 --- a/arch/arm/include/asm/signal.h +++ b/arch/arm/include/asm/signal.h @@ -17,6 +17,8 @@ typedef struct { unsigned long sig[_NSIG_WORDS]; } sigset_t; +#define __ARCH_UAPI_SA_FLAGS (SA_THIRTYTWO | SA_RESTORER) + #define __ARCH_HAS_SA_RESTORER #include diff --git a/arch/parisc/include/asm/signal.h b/arch/parisc/include/asm/signal.h index 715c96ba2ec8..30dd1e43ef88 100644 --- a/arch/parisc/include/asm/signal.h +++ b/arch/parisc/include/asm/signal.h @@ -21,6 +21,8 @@ typedef struct { unsigned long sig[_NSIG_WORDS]; } sigset_t; +#define __ARCH_UAPI_SA_FLAGS _SA_SIGGFAULT + #include #endif /* !__ASSEMBLY */ diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c index 9ccbf0576cd0..c599013ae8cb 100644 --- a/arch/x86/kernel/signal_compat.c +++ b/arch/x86/kernel/signal_compat.c @@ -165,16 +165,9 @@ void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact) { signal_compat_build_tests(); - /* Don't leak in-kernel non-uapi flags to user-space */ - if (oact) - oact->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI); - if (!act) return; - /* Don't let flags to be set from userspace */ - act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI); - if (in_ia32_syscall()) act->sa.sa_flags |= SA_IA32_ABI; if (in_x32_syscall()) diff --git a/include/linux/signal_types.h b/include/linux/signal_types.h index f8a90ae9c6ec..a7887ad84d36 100644 --- a/include/linux/signal_types.h +++ b/include/linux/signal_types.h @@ -68,4 +68,16 @@ struct ksignal { int sig; }; +#ifndef __ARCH_UAPI_SA_FLAGS +#ifdef SA_RESTORER +#define __ARCH_UAPI_SA_FLAGS SA_RESTORER +#else +#define __ARCH_UAPI_SA_FLAGS 0 +#endif +#endif + +#define UAPI_SA_FLAGS \ + (SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART | \ + SA_NODEFER | SA_RESETHAND | __ARCH_UAPI_SA_FLAGS) + #endif /* _LINUX_SIGNAL_TYPES_H */ diff --git a/kernel/signal.c b/kernel/signal.c index 42b67d2cea37..f802c82c7bcc 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3984,6 +3984,16 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact) if (oact) *oact = *k; + /* + * 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 + * internally. + */ + if (act) + act->sa.sa_flags &= UAPI_SA_FLAGS; + if (oact) + oact->sa.sa_flags &= UAPI_SA_FLAGS; + sigaction_compat_abi(act, oact); if (act) {