From patchwork Thu Mar 9 17:05:53 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Russell King (Oracle)" X-Patchwork-Id: 9613685 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 9F2E8604D9 for ; Thu, 9 Mar 2017 17:07:46 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8BBB6286A9 for ; Thu, 9 Mar 2017 17:07:46 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 7CA07286B9; Thu, 9 Mar 2017 17:07:46 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id F001D286A9 for ; Thu, 9 Mar 2017 17:07:44 +0000 (UTC) Received: (qmail 20359 invoked by uid 550); 9 Mar 2017 17:07:42 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 20330 invoked from network); 9 Mar 2017 17:07:42 -0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2014; h=Sender:In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date; bh=tzQtdnBXyr9bmRtSNhYKjBFP4lwu7TRP4QBe35GqWl0=; b=JjMrB5I0hqWoNA59rUGzUzei4kBbCgiroPIqBSzy8GsOwg06wW+V0BiASIlZ5CrlKgCjBYEsIHWotNzdp33a5X6tvVDEWZYRV3PpFbSz0dXbrX/+D5XlX3tAPVH9R/CdUYUWkCVWr8s0zNj94Wyz8qcV8deVXXXjxPVvPqn3qRc=; Date: Thu, 9 Mar 2017 17:05:53 +0000 From: Russell King - ARM Linux To: Thomas Garnier Cc: Mark Rutland , David Howells , Dave Hansen , Arnd Bergmann , Al Viro , =?iso-8859-1?Q?Ren=E9?= Nyffenegger , Andrew Morton , Kees Cook , "Paul E . McKenney" , "David S . Miller" , Andy Lutomirski , Ard Biesheuvel , Nicolas Pitre , Petr Mladek , Sebastian Andrzej Siewior , Sergey Senozhatsky , Helge Deller , Rik van Riel , Ingo Molnar , Oleg Nesterov , John Stultz , Thomas Gleixner , Pavel Tikhomirov , Frederic Weisbecker , Stephen Smalley , Stanislav Kinsburskiy , Ingo Molnar , "H . Peter Anvin" , Paolo Bonzini , Borislav Petkov , Josh Poimboeuf , Brian Gerst , Jan Beulich , Christian Borntraeger , "Luis R . Rodriguez" , He Chen , Will Deacon , Catalin Marinas , James Morse , Pratyush Anand , Vladimir Murzin , Chris Metcalf , Andre Przywara , Linux API , LKML , the arch/x86 maintainers , linux-arm-kernel@lists.infradead.org, Kernel Hardening Message-ID: <20170309170553.GO21222@n2100.armlinux.org.uk> References: <20170309012456.5631-1-thgarnie@google.com> <20170309012456.5631-4-thgarnie@google.com> <20170309122354.GB6320@leverpostej> <20170309162613.GN21222@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: Russell King - ARM Linux Subject: [kernel-hardening] Re: [PATCH v2 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state X-Virus-Scanned: ClamAV using ClamSMTP On Thu, Mar 09, 2017 at 08:35:30AM -0800, Thomas Garnier wrote: > On Thu, Mar 9, 2017 at 8:26 AM, Russell King - ARM Linux > wrote: > > I wouldn't call what you've done on ARM an "optimisation", because my > > comment about making the fast path worthless still stands. > > Why does it still stands on the latest proposal? It's still having to needlessly save stuff when there's nothing wrong. Remember, syscalls are a fast path, so the minimum we can do is good. Calling into C functions is not ideal, because they will tend to be _very_ expensive compared to hand crafted assembly, especially for something like this. It's possible to check the address limit in just three instructions, which is way less than will be incurred by calling a C function. Note: This patch is completely untested. arch/arm/kernel/entry-common.S | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index eb5cd77bf1d8..6b43c6d73117 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -41,8 +41,11 @@ UNWIND(.cantunwind ) disable_irq_notrace @ disable interrupts ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing + ldr r2, [tsk, #TI_ADDR_LIMIT] tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK bne fast_work_pending + cmp r2, #TASK_SIZE + blgt addr_limit_fail /* perform architecture specific actions before user return */ arch_ret_to_user r1, lr @@ -67,6 +70,7 @@ ENDPROC(ret_fast_syscall) str r0, [sp, #S_R0 + S_OFF]! @ save returned r0 disable_irq_notrace @ disable interrupts ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing + ldr r2, [tsk, #TI_ADDR_LIMIT] tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK beq no_work_pending UNWIND(.fnend ) @@ -82,6 +86,7 @@ ENDPROC(ret_fast_syscall) mov r2, why @ 'syscall' bl do_work_pending cmp r0, #0 + ldreq r2, [tsk, #TI_ADDR_LIMIT] beq no_work_pending movlt scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE) ldmia sp, {r0 - r6} @ have to reload r0 - r6 @@ -99,9 +104,12 @@ ENTRY(ret_to_user) disable_irq_notrace @ disable interrupts ENTRY(ret_to_user_from_irq) ldr r1, [tsk, #TI_FLAGS] + ldr r2, [tsk, #TI_ADDR_LIMIT] tst r1, #_TIF_WORK_MASK bne slow_work_pending no_work_pending: + cmp r2, #TASK_SIZE + blgt addr_limit_fail asm_trace_hardirqs_on save = 0 /* perform architecture specific actions before user return */ @@ -125,6 +133,16 @@ ENTRY(ret_from_fork) b ret_slow_syscall ENDPROC(ret_from_fork) +addr_limit_fail: +#ifdef CONFIG_BUG_ON_DATA_CORRUPTION + stmfd sp!, {r0, lr} + bl verify_pre_usermode_state + ldmfd sp!, {r0, lr} +#endif + mov r2, #TASK_SIZE + str r2, [tsk, #TI_ADDR_LIMIT] + ret lr + /*============================================================================= * SWI handler *-----------------------------------------------------------------------------