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 X-Spam-Level: X-Spam-Status: No, score=-10.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 3669FC43444 for ; Fri, 11 Jan 2019 15:06:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0792520874 for ; Fri, 11 Jan 2019 15:06:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547219217; bh=0VA1UcJ6A1fDK36+YFfbPQLFIVDwdStFVXmiTdC9GuM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NqxJUNmhFDrBrOZs+pguRZEAvIN4n1YjZtUFYYetJHDQa5NZmTpxaar3nHsRuIV2T VJY1kHUBAU6PDirSrttJV1ov4YnljHLS9tj7ESW9a0l7QrH9IHgqTaDagGN18p4MkF IHwWfB0n3t4+ZlDIJQrbUx6wBrZ62bOUGTeJQLnA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387606AbfAKO2t (ORCPT ); Fri, 11 Jan 2019 09:28:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:47584 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388571AbfAKO2q (ORCPT ); Fri, 11 Jan 2019 09:28:46 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AE16821841; Fri, 11 Jan 2019 14:28:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547216925; bh=0VA1UcJ6A1fDK36+YFfbPQLFIVDwdStFVXmiTdC9GuM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OxgDXtoPo9DD7KKfGg5mCG0Jgvpu17NCYOfCOwYkWEqDGc0PKyXhD379HX5rVd7DG bfeFJwVq79gFxIsOr99vQTmCRktlTdJXZwOlD/D5QZnvK80GgbzIoZWg0hwguVEfrF fp+XbsI30SPjQHuapCi6bQB83FlDnHcjnSI/2wYM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andy Lutomirski , Paul Burton , linux-mips@vger.kernel.org, Rich Felker , David Daney Subject: [PATCH 4.9 41/63] MIPS: math-emu: Write-protect delay slot emulation pages Date: Fri, 11 Jan 2019 15:14:44 +0100 Message-Id: <20190111131052.421721088@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190111131046.387528003@linuxfoundation.org> References: <20190111131046.387528003@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul Burton commit adcc81f148d733b7e8e641300c5590a2cdc13bf3 upstream. Mapping the delay slot emulation page as both writeable & executable presents a security risk, in that if an exploit can write to & jump into the page then it can be used as an easy way to execute arbitrary code. Prevent this by mapping the page read-only for userland, and using access_process_vm() with the FOLL_FORCE flag to write to it from mips_dsemul(). This will likely be less efficient due to copy_to_user_page() performing cache maintenance on a whole page, rather than a single line as in the previous use of flush_cache_sigtramp(). However this delay slot emulation code ought not to be running in any performance critical paths anyway so this isn't really a problem, and we can probably do better in copy_to_user_page() anyway in future. A major advantage of this approach is that the fix is small & simple to backport to stable kernels. Reported-by: Andy Lutomirski Signed-off-by: Paul Burton Fixes: 432c6bacbd0c ("MIPS: Use per-mm page to execute branch delay slot instructions") Cc: stable@vger.kernel.org # v4.8+ Cc: linux-mips@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Rich Felker Cc: David Daney Signed-off-by: Greg Kroah-Hartman --- arch/mips/kernel/vdso.c | 4 ++-- arch/mips/math-emu/dsemul.c | 38 ++++++++++++++++++++------------------ 2 files changed, 22 insertions(+), 20 deletions(-) --- a/arch/mips/kernel/vdso.c +++ b/arch/mips/kernel/vdso.c @@ -111,8 +111,8 @@ int arch_setup_additional_pages(struct l /* Map delay slot emulation page */ base = mmap_region(NULL, STACK_TOP, PAGE_SIZE, - VM_READ|VM_WRITE|VM_EXEC| - VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, + VM_READ | VM_EXEC | + VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC, 0); if (IS_ERR_VALUE(base)) { ret = base; --- a/arch/mips/math-emu/dsemul.c +++ b/arch/mips/math-emu/dsemul.c @@ -211,8 +211,9 @@ int mips_dsemul(struct pt_regs *regs, mi { int isa16 = get_isa16_mode(regs->cp0_epc); mips_instruction break_math; - struct emuframe __user *fr; - int err, fr_idx; + unsigned long fr_uaddr; + struct emuframe fr; + int fr_idx, ret; /* NOP is easy */ if (ir == 0) @@ -247,27 +248,31 @@ int mips_dsemul(struct pt_regs *regs, mi fr_idx = alloc_emuframe(); if (fr_idx == BD_EMUFRAME_NONE) return SIGBUS; - fr = &dsemul_page()[fr_idx]; /* Retrieve the appropriately encoded break instruction */ break_math = BREAK_MATH(isa16); /* Write the instructions to the frame */ if (isa16) { - err = __put_user(ir >> 16, - (u16 __user *)(&fr->emul)); - err |= __put_user(ir & 0xffff, - (u16 __user *)((long)(&fr->emul) + 2)); - err |= __put_user(break_math >> 16, - (u16 __user *)(&fr->badinst)); - err |= __put_user(break_math & 0xffff, - (u16 __user *)((long)(&fr->badinst) + 2)); + union mips_instruction _emul = { + .halfword = { ir >> 16, ir } + }; + union mips_instruction _badinst = { + .halfword = { break_math >> 16, break_math } + }; + + fr.emul = _emul.word; + fr.badinst = _badinst.word; } else { - err = __put_user(ir, &fr->emul); - err |= __put_user(break_math, &fr->badinst); + fr.emul = ir; + fr.badinst = break_math; } - if (unlikely(err)) { + /* Write the frame to user memory */ + fr_uaddr = (unsigned long)&dsemul_page()[fr_idx]; + ret = access_process_vm(current, fr_uaddr, &fr, sizeof(fr), + FOLL_FORCE | FOLL_WRITE); + if (unlikely(ret != sizeof(fr))) { MIPS_FPU_EMU_INC_STATS(errors); free_emuframe(fr_idx, current->mm); return SIGBUS; @@ -279,10 +284,7 @@ int mips_dsemul(struct pt_regs *regs, mi atomic_set(¤t->thread.bd_emu_frame, fr_idx); /* Change user register context to execute the frame */ - regs->cp0_epc = (unsigned long)&fr->emul | isa16; - - /* Ensure the icache observes our newly written frame */ - flush_cache_sigtramp((unsigned long)&fr->emul); + regs->cp0_epc = fr_uaddr | isa16; return 0; }