From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753048AbaIDOAf (ORCPT ); Thu, 4 Sep 2014 10:00:35 -0400 Received: from mail-oi0-f54.google.com ([209.85.218.54]:49195 "EHLO mail-oi0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750967AbaIDOAc (ORCPT ); Thu, 4 Sep 2014 10:00:32 -0400 MIME-Version: 1.0 In-Reply-To: <20140904092720.GA7156@arm.com> References: <1407949593-16121-1-git-send-email-keescook@chromium.org> <1407949593-16121-5-git-send-email-keescook@chromium.org> <20140819122933.GI23128@arm.com> <20140904092720.GA7156@arm.com> Date: Thu, 4 Sep 2014 07:00:31 -0700 X-Google-Sender-Auth: LBA7ykGuVFYl6g8n-PEsq1E9SH4 Message-ID: Subject: Re: [PATCH v4 4/8] arm: use fixmap for text patching when text is RO From: Kees Cook To: Will Deacon Cc: "linux-kernel@vger.kernel.org" , Rabin Vincent , Rob Herring , Laura Abbott , Leif Lindholm , Stephen Boyd , "msalter@redhat.com" , Liu hua , Nikolay Borisov , Nicolas Pitre , Tomasz Figa , Doug Anderson , Jason Wessel , Catalin Marinas , Russell King - ARM Linux , "linux-arm-kernel@lists.infradead.org" , "linux-doc@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 4, 2014 at 2:27 AM, Will Deacon wrote: > On Wed, Sep 03, 2014 at 10:43:58PM +0100, Kees Cook wrote: >> On Wed, Aug 20, 2014 at 5:28 AM, Kees Cook wrote: >> > On Tue, Aug 19, 2014 at 7:29 AM, Will Deacon wrote: >> >> On Wed, Aug 13, 2014 at 06:06:29PM +0100, Kees Cook wrote: >> >>> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags) >> >>> + __acquires(&patch_lock) >> >>> +{ >> >>> + unsigned int uintaddr = (uintptr_t) addr; >> >>> + bool module = !core_kernel_text(uintaddr); >> >>> + struct page *page; >> >>> + >> >>> + if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) >> >>> + page = vmalloc_to_page(addr); >> >>> + else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA)) >> >>> + page = virt_to_page(addr); >> >>> + else >> >>> + return addr; >> >>> + >> >>> + if (flags) >> >>> + spin_lock_irqsave(&patch_lock, *flags); >> >>> + else >> >>> + __acquire(&patch_lock); >> >> >> >> I don't understand the locking here. Why is it conditional, why do we need >> >> to disable interrupts, and are you just racing against yourself? >> > >> > AIUI, the locking is here to avoid multiple users of the text poking >> > fixmaps. It's conditional because there are two fixmaps >> > (FIX_TEXT_POKE0 and FIX_TEXT_POKE1). Locking happens around 0 so >> > locking around 1 is not needed since it is only ever used when 0 is in >> > use. (__patch_text_real locks patch_lock before setting 0 when it uses >> > remapping, and if it also needs 1, it doesn't have to lock since the >> > lock is already held.) >> > >> >>> + set_fixmap(fixmap, page_to_phys(page)); >> >> >> >> set_fixmap does TLB invalidation, right? I think that means it can block on >> >> 11MPCore and A15 w/ the TLBI erratum, so it's not safe to call this with >> >> interrupts disabled anyway. >> > >> > Oh right. Hrm. >> > >> > In an earlier version of this series set_fixmap did not perform TLB >> > invalidation. I wonder if this is not needed at all? (Wouldn't that be >> > nice...) >> >> As suspected, my tests fail spectacularly without the TLB flush. >> Adding WARN_ON(!irqs_disabled()) doesn't warn, so I think we're safe >> here. Should I leave the WARN_ON in place for clarity, or some other >> comments? > > I thought there was a potential call to spin_lock_irqsave right before > this TLB flush? I'm not sure I understand what you mean. Should I change something here? It looks like irqs are disabled, so isn't this a safe code path? -Kees -- Kees Cook Chrome OS Security From mboxrd@z Thu Jan 1 00:00:00 1970 From: keescook@chromium.org (Kees Cook) Date: Thu, 4 Sep 2014 07:00:31 -0700 Subject: [PATCH v4 4/8] arm: use fixmap for text patching when text is RO In-Reply-To: <20140904092720.GA7156@arm.com> References: <1407949593-16121-1-git-send-email-keescook@chromium.org> <1407949593-16121-5-git-send-email-keescook@chromium.org> <20140819122933.GI23128@arm.com> <20140904092720.GA7156@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Sep 4, 2014 at 2:27 AM, Will Deacon wrote: > On Wed, Sep 03, 2014 at 10:43:58PM +0100, Kees Cook wrote: >> On Wed, Aug 20, 2014 at 5:28 AM, Kees Cook wrote: >> > On Tue, Aug 19, 2014 at 7:29 AM, Will Deacon wrote: >> >> On Wed, Aug 13, 2014 at 06:06:29PM +0100, Kees Cook wrote: >> >>> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags) >> >>> + __acquires(&patch_lock) >> >>> +{ >> >>> + unsigned int uintaddr = (uintptr_t) addr; >> >>> + bool module = !core_kernel_text(uintaddr); >> >>> + struct page *page; >> >>> + >> >>> + if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX)) >> >>> + page = vmalloc_to_page(addr); >> >>> + else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA)) >> >>> + page = virt_to_page(addr); >> >>> + else >> >>> + return addr; >> >>> + >> >>> + if (flags) >> >>> + spin_lock_irqsave(&patch_lock, *flags); >> >>> + else >> >>> + __acquire(&patch_lock); >> >> >> >> I don't understand the locking here. Why is it conditional, why do we need >> >> to disable interrupts, and are you just racing against yourself? >> > >> > AIUI, the locking is here to avoid multiple users of the text poking >> > fixmaps. It's conditional because there are two fixmaps >> > (FIX_TEXT_POKE0 and FIX_TEXT_POKE1). Locking happens around 0 so >> > locking around 1 is not needed since it is only ever used when 0 is in >> > use. (__patch_text_real locks patch_lock before setting 0 when it uses >> > remapping, and if it also needs 1, it doesn't have to lock since the >> > lock is already held.) >> > >> >>> + set_fixmap(fixmap, page_to_phys(page)); >> >> >> >> set_fixmap does TLB invalidation, right? I think that means it can block on >> >> 11MPCore and A15 w/ the TLBI erratum, so it's not safe to call this with >> >> interrupts disabled anyway. >> > >> > Oh right. Hrm. >> > >> > In an earlier version of this series set_fixmap did not perform TLB >> > invalidation. I wonder if this is not needed at all? (Wouldn't that be >> > nice...) >> >> As suspected, my tests fail spectacularly without the TLB flush. >> Adding WARN_ON(!irqs_disabled()) doesn't warn, so I think we're safe >> here. Should I leave the WARN_ON in place for clarity, or some other >> comments? > > I thought there was a potential call to spin_lock_irqsave right before > this TLB flush? I'm not sure I understand what you mean. Should I change something here? It looks like irqs are disabled, so isn't this a safe code path? -Kees -- Kees Cook Chrome OS Security