From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2 0/6] x86/alternatives: text_poke() fixes Date: Thu, 6 Sep 2018 19:17:54 +0200 Message-ID: <20180906171754.GJ24106@hirez.programming.kicks-ass.net> References: <20180902173224.30606-1-namit@vmware.com> <20180905185617.GC24082@hirez.programming.kicks-ass.net> <8D3CE999-6D3A-4984-934A-634BDD8AC25A@vmware.com> <6B256AB7-0158-47DF-B2D5-4C835579F3A3@vmware.com> <20180906081300.GF24082@hirez.programming.kicks-ass.net> <20180906101641.GG24142@hirez.programming.kicks-ass.net> <6703CD9F-2D84-4449-A423-A4DC24677673@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <6703CD9F-2D84-4449-A423-A4DC24677673@vmware.com> Sender: linux-kernel-owner@vger.kernel.org To: Nadav Amit Cc: Thomas Gleixner , LKML , Ingo Molnar , X86 ML , Arnd Bergmann , linux-arch , Dave Hansen , Jiri Kosina , Andy Lutomirski , Masami Hiramatsu , Kees Cook List-Id: linux-arch.vger.kernel.org On Thu, Sep 06, 2018 at 05:01:25PM +0000, Nadav Amit wrote: > In addition, there might be a couple of issues with your fix: It boots on my box ;-) > 1. __set_pte_vaddr() is not used exclusive by set_fixmap(). This means > the warning might be wrong, but also means that these code patches (Xen’s > set_pte_mfn(), CPU-entry-area setup) needs to be checked. And as you said > before, someone might use this function for other purposes as well. CEA is fine, that actually needs it too. The one thing I missed out on earlier is the below chunk, that is no longer needed now that cea_set_pte() actually does the right thing. diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index b7b01d762d32..14ad97fa0749 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -293,12 +293,6 @@ static void ds_update_cea(void *cea, void *addr, size_t size, pgprot_t prot) preempt_disable(); for (; msz < size; msz += PAGE_SIZE, pa += PAGE_SIZE, cea += PAGE_SIZE) cea_set_pte(cea, pa, prot); - - /* - * This is a cross-CPU update of the cpu_entry_area, we must shoot down - * all TLB entries for it. - */ - flush_tlb_kernel_range(start, start + size); preempt_enable(); } @@ -310,8 +304,6 @@ static void ds_clear_cea(void *cea, size_t size) preempt_disable(); for (; msz < size; msz += PAGE_SIZE, cea += PAGE_SIZE) cea_set_pte(cea, 0, PAGE_NONE); - - flush_tlb_kernel_range(start, start + size); preempt_enable(); } > 2. Printing the virtual address can break KASLR. Local KASLR is a myth.. but sure, we can fix the print. > 3. The WARN() can introduce some overhead since checking if IRQs are > disabled takes considerably long time. Perhaps VM_WARN() or something is > better. I realize this code-path is not on the hot-path though... Yeah, if it triggers you have bigger problems. We can make it WARN_ONCE() I suppose. > 4. I guess flush_tlb_kernel_range() should also have something like > VM_WARN_ON(irqs_disabled()), just as an additional general sanity check. It has, it's hidden in kernel/smp.c:smp_call_function_many(). > Let me know if you want me to make these changes and include your patch in > the set. The set is no longer needed. text_poke() is fine and correct with this one patch. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:49460 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728074AbeIFVy1 (ORCPT ); Thu, 6 Sep 2018 17:54:27 -0400 Date: Thu, 6 Sep 2018 19:17:54 +0200 From: Peter Zijlstra Subject: Re: [PATCH v2 0/6] x86/alternatives: text_poke() fixes Message-ID: <20180906171754.GJ24106@hirez.programming.kicks-ass.net> References: <20180902173224.30606-1-namit@vmware.com> <20180905185617.GC24082@hirez.programming.kicks-ass.net> <8D3CE999-6D3A-4984-934A-634BDD8AC25A@vmware.com> <6B256AB7-0158-47DF-B2D5-4C835579F3A3@vmware.com> <20180906081300.GF24082@hirez.programming.kicks-ass.net> <20180906101641.GG24142@hirez.programming.kicks-ass.net> <6703CD9F-2D84-4449-A423-A4DC24677673@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6703CD9F-2D84-4449-A423-A4DC24677673@vmware.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Nadav Amit Cc: Thomas Gleixner , LKML , Ingo Molnar , X86 ML , Arnd Bergmann , linux-arch , Dave Hansen , Jiri Kosina , Andy Lutomirski , Masami Hiramatsu , Kees Cook Message-ID: <20180906171754.aHTuWncjZQmWolEgMEZhcr_BBRD3r_phV-CV5MW9aM8@z> On Thu, Sep 06, 2018 at 05:01:25PM +0000, Nadav Amit wrote: > In addition, there might be a couple of issues with your fix: It boots on my box ;-) > 1. __set_pte_vaddr() is not used exclusive by set_fixmap(). This means > the warning might be wrong, but also means that these code patches (Xen’s > set_pte_mfn(), CPU-entry-area setup) needs to be checked. And as you said > before, someone might use this function for other purposes as well. CEA is fine, that actually needs it too. The one thing I missed out on earlier is the below chunk, that is no longer needed now that cea_set_pte() actually does the right thing. diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index b7b01d762d32..14ad97fa0749 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -293,12 +293,6 @@ static void ds_update_cea(void *cea, void *addr, size_t size, pgprot_t prot) preempt_disable(); for (; msz < size; msz += PAGE_SIZE, pa += PAGE_SIZE, cea += PAGE_SIZE) cea_set_pte(cea, pa, prot); - - /* - * This is a cross-CPU update of the cpu_entry_area, we must shoot down - * all TLB entries for it. - */ - flush_tlb_kernel_range(start, start + size); preempt_enable(); } @@ -310,8 +304,6 @@ static void ds_clear_cea(void *cea, size_t size) preempt_disable(); for (; msz < size; msz += PAGE_SIZE, cea += PAGE_SIZE) cea_set_pte(cea, 0, PAGE_NONE); - - flush_tlb_kernel_range(start, start + size); preempt_enable(); } > 2. Printing the virtual address can break KASLR. Local KASLR is a myth.. but sure, we can fix the print. > 3. The WARN() can introduce some overhead since checking if IRQs are > disabled takes considerably long time. Perhaps VM_WARN() or something is > better. I realize this code-path is not on the hot-path though... Yeah, if it triggers you have bigger problems. We can make it WARN_ONCE() I suppose. > 4. I guess flush_tlb_kernel_range() should also have something like > VM_WARN_ON(irqs_disabled()), just as an additional general sanity check. It has, it's hidden in kernel/smp.c:smp_call_function_many(). > Let me know if you want me to make these changes and include your patch in > the set. The set is no longer needed. text_poke() is fine and correct with this one patch.