Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934251AbdDGQMZ (ORCPT ); Fri, 7 Apr 2017 12:12:25 -0400 Received: from foss.arm.com ([217.140.101.70]:57874 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934217AbdDGQMN (ORCPT ); Fri, 7 Apr 2017 12:12:13 -0400 Date: Fri, 7 Apr 2017 17:11:59 +0100 From: Catalin Marinas To: Thomas Garnier Cc: Mark Rutland , Kernel Hardening , Will Deacon , Oleg Nesterov , David Howells , Dave Hansen , "H . Peter Anvin" , Ingo Molnar , Pavel Tikhomirov , linux-s390 , the arch/x86 maintainers , Russell King , Christian Borntraeger , =?iso-8859-1?Q?Ren=E9?= Nyffenegger , Brian Gerst , "Paul E . McKenney" , Stephen Smalley , Rik van Riel , Kees Cook , Arnd Bergmann , Heiko Carstens , Borislav Petkov , Al Viro , Andy Lutomirski , Josh Poimboeuf , Thomas Gleixner , Ingo Molnar , linux-arm-kernel@lists.infradead.org, Linux API , LKML , James Morse , Martin Schwidefsky , Paolo Bonzini , Andrew Morton , "Kirill A . Shutemov" Subject: Re: [PATCH v6 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state Message-ID: <20170407161159.GB20645@e104818-lin.cambridge.arm.com> References: <20170404174727.35478-1-thgarnie@google.com> <20170404174727.35478-4-thgarnie@google.com> <20170405142225.GA9072@e104818-lin.cambridge.arm.com> <20170405174921.GB2752@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2015 Lines: 48 On Wed, Apr 05, 2017 at 11:14:34AM -0700, Thomas Garnier wrote: > On Wed, Apr 5, 2017 at 10:49 AM, Catalin Marinas > wrote: > > On Wed, Apr 05, 2017 at 07:36:17AM -0700, Thomas Garnier wrote: > >> On Wed, Apr 5, 2017 at 7:22 AM, Catalin Marinas wrote: > >> > On Tue, Apr 04, 2017 at 10:47:27AM -0700, Thomas Garnier wrote: > >> >> + > >> >> ldr x1, [tsk, #TSK_TI_FLAGS] > >> >> and x2, x1, #_TIF_WORK_MASK > >> >> cbnz x2, work_pending > >> >> @@ -779,6 +788,12 @@ finish_ret_to_user: > >> >> kernel_exit 0 > >> >> ENDPROC(ret_to_user) > >> >> > >> >> +addr_limit_fail: > >> >> + stp x0, lr, [sp,#-16]! > >> >> + bl asm_verify_pre_usermode_state > >> >> + ldp x0, lr, [sp],#16 > >> >> + ret lr > >> > > >> > Where is this supposed to return? What is the value of lr when branching > >> > to addr_limit_fail? > >> > >> It is not supposed to return. Do you think I should remove stp, ldp, > >> ret and jut add a brk 0x100 or jmp/call a break/bug function? > > > > Can you not just make addr_limit_fail a C function which never returns > > (similar to what we to with bad_mode() on arm64)? Since addr_limit_fail > > is only called when the segment is not the right one, I don't really see > > why you need another call to asm_verify_pre_usermode_state() to do a > > similar check again. Just panic in addr_limit_fail (unless I > > misunderstood what you are trying to achieve). > > Calling asm_verify_pre_usermode_state has the advantage of having a > clear BUG_ON for the error (versus a panic description). > > What do you think about replacing asm_verify_pre_usermode_state by a > "address_limit_fail" function that still calls > verify_pre_usermode_state but panic afterwards (because it should > never return)? > > The assembly code would be easier to understand and in case of error > the BUG_ON is clear for the user. It looks fine to me, though I'd have to see the patch. -- Catalin