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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A079FC433EF for ; Mon, 18 Oct 2021 13:32:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8596761357 for ; Mon, 18 Oct 2021 13:32:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232790AbhJRNfD (ORCPT ); Mon, 18 Oct 2021 09:35:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:43688 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232134AbhJRNdT (ORCPT ); Mon, 18 Oct 2021 09:33:19 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C87B7613A0; Mon, 18 Oct 2021 13:29:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1634563777; bh=tKdSaJ4ky4rkcucRDq96qoY0E2exYgCClISb3PmPDUY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dLUjN0CjNcNQhrAOieAhy4CD3QHGwquSRQhXnGof4ntqqyy9ZLMN0UGUzF0knGt3z 3C1608DVbuanBiOZIN5HCI3ACXCWvP22DNeEdCdxP5KSizcGZv0LDVKn6h4ggj/ZQW YAyEgaEIlKcSdfW9b503NQ/QxOZEScnpAxrxk5wM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Al Viro , Guo Ren Subject: [PATCH 5.4 10/69] csky: dont let sigreturn play with priveleged bits of status register Date: Mon, 18 Oct 2021 15:24:08 +0200 Message-Id: <20211018132329.795936051@linuxfoundation.org> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20211018132329.453964125@linuxfoundation.org> References: <20211018132329.453964125@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Al Viro commit fbd63c08cdcca5fb1315aca3172b3c9c272cfb4f upstream. csky restore_sigcontext() blindly overwrites regs->sr with the value it finds in sigcontext. Attacker can store whatever they want in there, which includes things like S-bit. Userland shouldn't be able to set that, or anything other than C flag (bit 0). Do the same thing other architectures with protected bits in flags register do - preserve everything that shouldn't be settable in user mode, picking the rest from the value saved is sigcontext. Signed-off-by: Al Viro Signed-off-by: Guo Ren Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman --- arch/csky/kernel/signal.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/arch/csky/kernel/signal.c +++ b/arch/csky/kernel/signal.c @@ -52,10 +52,14 @@ static long restore_sigcontext(struct pt struct sigcontext __user *sc) { int err = 0; + unsigned long sr = regs->sr; /* sc_pt_regs is structured the same as the start of pt_regs */ err |= __copy_from_user(regs, &sc->sc_pt_regs, sizeof(struct pt_regs)); + /* BIT(0) of regs->sr is Condition Code/Carry bit */ + regs->sr = (sr & ~1) | (regs->sr & 1); + /* Restore the floating-point state. */ err |= restore_fpu_state(sc);