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 EFBB4C433F5 for ; Sat, 25 Sep 2021 05:17:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C47AF61151 for ; Sat, 25 Sep 2021 05:17:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233877AbhIYFSj (ORCPT ); Sat, 25 Sep 2021 01:18:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:50466 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230453AbhIYFSj (ORCPT ); Sat, 25 Sep 2021 01:18:39 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 397BA610EA; Sat, 25 Sep 2021 05:17:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1632547024; bh=2nPifVqIq6xS4+2b04wivl+7zS28QpMII0hRXZFD2mY=; h=From:To:Cc:Subject:Date:From; b=g4YMFKDHiF+PrrXeO5hAycwq2NaxJTJurEYEuJ8lQhnX0cz2u6l1N9WP5wQjU8AC1 VQ3djwfvCaXIXTZ03flbeV2LOUru5CcfjujHyvyf9XqzOb593IVo3Nhp5hMdvPOmKs ngTQPB8BUaHYJWlYcd8e360fKhT3QIVPXAItFgfz6D3lMOe8Q7rYuNBsFzzMguv6TF n7jQttUZIn3iXi34QrQD302sKq/MfAi0ad6ZPykp/xJuyo49ixyNuo0VGcn1h0hXk1 zgBdT3tUE9RoUePTJSxC24bU9TF6v2GIdiitCiRMdiqRcH86qzfgmNLifP2qTawN8u bawatllA3YVzQ== From: guoren@kernel.org To: guoren@kernel.org Cc: linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, Al Viro , stable@vger.kernel.org Subject: [PATCH V2 1/2] csky: don't let sigreturn play with priveleged bits of status register Date: Sat, 25 Sep 2021 13:16:46 +0800 Message-Id: <20210925051647.1162829-1-guoren@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org From: Al Viro 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 --- arch/csky/kernel/signal.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c index 312f046d452d..6ba3969ec175 100644 --- a/arch/csky/kernel/signal.c +++ b/arch/csky/kernel/signal.c @@ -52,10 +52,14 @@ static long restore_sigcontext(struct pt_regs *regs, 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); -- 2.25.1