From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756825AbaICVoB (ORCPT ); Wed, 3 Sep 2014 17:44:01 -0400 Received: from mail-ob0-f172.google.com ([209.85.214.172]:38405 "EHLO mail-ob0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754925AbaICVn7 (ORCPT ); Wed, 3 Sep 2014 17:43:59 -0400 MIME-Version: 1.0 In-Reply-To: References: <1407949593-16121-1-git-send-email-keescook@chromium.org> <1407949593-16121-5-git-send-email-keescook@chromium.org> <20140819122933.GI23128@arm.com> Date: Wed, 3 Sep 2014 14:43:58 -0700 X-Google-Sender-Auth: Py3lmKb63Qff5NSefNTBJruQzWk 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 Wed, Aug 20, 2014 at 5:28 AM, Kees Cook wrote: > On Tue, Aug 19, 2014 at 7:29 AM, Will Deacon wrote: >> Hello, >> >> On Wed, Aug 13, 2014 at 06:06:29PM +0100, Kees Cook wrote: >>> From: Rabin Vincent >>> >>> Use fixmaps for text patching when the kernel text is read-only, >>> inspired by x86. This makes jump labels and kprobes work with the >>> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming >>> CONFIG_DEBUG_RODATA options. >>> >>> Signed-off-by: Rabin Vincent >>> [kees: fixed up for merge with "arm: use generic fixmap.h"] >>> [kees: added parse acquire/release annotations to pass C=1 builds] >>> Signed-off-by: Kees Cook >> >> [...] >> >>> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c >>> index 07314af47733..a1dce690446a 100644 >>> --- a/arch/arm/kernel/patch.c >>> +++ b/arch/arm/kernel/patch.c >>> @@ -1,8 +1,11 @@ >>> #include >>> +#include >>> #include >>> +#include >>> #include >>> >>> #include >>> +#include >>> #include >>> #include >>> >>> @@ -13,21 +16,77 @@ struct patch { >>> unsigned int insn; >>> }; >>> >>> -void __kprobes __patch_text(void *addr, unsigned int insn) >>> +static DEFINE_SPINLOCK(patch_lock); >>> + >>> +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? -Kees -- Kees Cook Chrome OS Security From mboxrd@z Thu Jan 1 00:00:00 1970 From: keescook@chromium.org (Kees Cook) Date: Wed, 3 Sep 2014 14:43:58 -0700 Subject: [PATCH v4 4/8] arm: use fixmap for text patching when text is RO In-Reply-To: References: <1407949593-16121-1-git-send-email-keescook@chromium.org> <1407949593-16121-5-git-send-email-keescook@chromium.org> <20140819122933.GI23128@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Aug 20, 2014 at 5:28 AM, Kees Cook wrote: > On Tue, Aug 19, 2014 at 7:29 AM, Will Deacon wrote: >> Hello, >> >> On Wed, Aug 13, 2014 at 06:06:29PM +0100, Kees Cook wrote: >>> From: Rabin Vincent >>> >>> Use fixmaps for text patching when the kernel text is read-only, >>> inspired by x86. This makes jump labels and kprobes work with the >>> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming >>> CONFIG_DEBUG_RODATA options. >>> >>> Signed-off-by: Rabin Vincent >>> [kees: fixed up for merge with "arm: use generic fixmap.h"] >>> [kees: added parse acquire/release annotations to pass C=1 builds] >>> Signed-off-by: Kees Cook >> >> [...] >> >>> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c >>> index 07314af47733..a1dce690446a 100644 >>> --- a/arch/arm/kernel/patch.c >>> +++ b/arch/arm/kernel/patch.c >>> @@ -1,8 +1,11 @@ >>> #include >>> +#include >>> #include >>> +#include >>> #include >>> >>> #include >>> +#include >>> #include >>> #include >>> >>> @@ -13,21 +16,77 @@ struct patch { >>> unsigned int insn; >>> }; >>> >>> -void __kprobes __patch_text(void *addr, unsigned int insn) >>> +static DEFINE_SPINLOCK(patch_lock); >>> + >>> +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? -Kees -- Kees Cook Chrome OS Security