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[209.132.180.67]) by mx.google.com with ESMTP id 142-v6si429031pfy.182.2018.08.27.15.33.34; Mon, 27 Aug 2018 15:33:50 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=OE3Njbzk; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727180AbeH1CVC (ORCPT + 99 others); Mon, 27 Aug 2018 22:21:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:51006 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726994AbeH1CVB (ORCPT ); Mon, 27 Aug 2018 22:21:01 -0400 Received: from mail-wm0-f42.google.com (mail-wm0-f42.google.com [74.125.82.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 60CB020C51 for ; Mon, 27 Aug 2018 22:32:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1535409144; bh=4rE5euCS0ZZzeEld6AsWMWBmTEzTA28YXRgykM/JVVM=; h=In-Reply-To:References:From:Date:Subject:To:Cc:From; b=OE3Njbzk723H6gWSyC9EhTTOr0wMZhrIiNSNzV1yPwOsq6cEQ0zLaCCYjBRF4V3ju Bg1uCky1ak8CwSN1U3Ex5fCMRXNNTGY0lrkypPbGDaSgv5KipAE0G6c4nHnfoLr328 uYoQvdLsiQEpdHKJ9ZmRSbyqrxgqSzMCJQ5ikwoQ= Received: by mail-wm0-f42.google.com with SMTP id 207-v6so446252wme.5 for ; Mon, 27 Aug 2018 15:32:24 -0700 (PDT) X-Gm-Message-State: APzg51CATCBA2dc4nopNsI9R50wRhd+3scXL0K5PlkgaZacyxwDEetOO dG1GgtLUrtDnsoExX1U21Q8md0BhsmNHnPQa2C3ptA== X-Received: by 2002:a1c:8313:: with SMTP id f19-v6mr6415478wmd.144.1535409142561; Mon, 27 Aug 2018 15:32:22 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a1c:548:0:0:0:0:0 with HTTP; Mon, 27 Aug 2018 15:32:02 -0700 (PDT) In-Reply-To: <4F72D40A-25A3-4C64-B8DD-56970CFDE61E@gmail.com> References: <20180824180438.GS24124@hirez.programming.kicks-ass.net> <56A9902F-44BE-4520-A17C-26650FCC3A11@gmail.com> <9A38D3F4-2F75-401D-8B4D-83A844C9061B@gmail.com> <8E0D8C66-6F21-4890-8984-B6B3082D4CC5@gmail.com> <20180826112341.f77a528763e297cbc36058fa@kernel.org> <20180826090958.GT24124@hirez.programming.kicks-ass.net> <20180827120305.01a6f26267c64610cadec5d8@kernel.org> <4BF82052-4738-441C-8763-26C85003F2C9@gmail.com> <20180827170511.6bafa15cbc102ae135366e86@kernel.org> <01DA0BDD-7504-4209-8A8F-20B27CF6A1C7@gmail.com> <0000D631-FDDF-4273-8F3C-714E6825E59B@gmail.com> <823D916E-4056-4A36-BDD8-0FB682A8DCAE@gmail.com> <08A6BCB2-66C2-47ED-AEB8-AA8F4D7DBD45@gmail.com> <4F72D40A-25A3-4C64-B8DD-56970CFDE61E@gmail.com> From: Andy Lutomirski Date: Mon, 27 Aug 2018 15:32:02 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: TLB flushes on fixmap changes To: Nadav Amit Cc: Andy Lutomirski , Masami Hiramatsu , Peter Zijlstra , Kees Cook , Linus Torvalds , Paolo Bonzini , Jiri Kosina , Will Deacon , Benjamin Herrenschmidt , Nick Piggin , "the arch/x86 maintainers" , Borislav Petkov , Rik van Riel , Jann Horn , Adin Scannell , Dave Hansen , Linux Kernel Mailing List , linux-mm , David Miller , Martin Schwidefsky , Michael Ellerman Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 27, 2018 at 2:55 PM, Nadav Amit wrote: > at 1:16 PM, Nadav Amit wrote: > >> at 12:58 PM, Andy Lutomirski wrote: >> >>> On Mon, Aug 27, 2018 at 12:43 PM, Nadav Amit wro= te: >>>> at 12:10 PM, Nadav Amit wrote: >>>> >>>>> at 11:58 AM, Andy Lutomirski wrote: >>>>> >>>>>> On Mon, Aug 27, 2018 at 11:54 AM, Nadav Amit = wrote: >>>>>>>> On Mon, Aug 27, 2018 at 10:34 AM, Nadav Amit wrote: >>>>>>>> What do you all think? >>>>>>> >>>>>>> I agree in general. But I think that current->mm would need to be l= oaded, as >>>>>>> otherwise I am afraid it would break switch_mm_irqs_off(). >>>>>> >>>>>> What breaks? >>>>> >>>>> Actually nothing. I just saw the IBPB stuff regarding tsk, but it sho= uld not >>>>> matter. >>>> >>>> So here is what I got. It certainly needs some cleanup, but it boots. >>>> >>>> Let me know how crappy you find it... >>>> >>>> >>>> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm= /mmu_context.h >>>> index bbc796eb0a3b..336779650a41 100644 >>>> --- a/arch/x86/include/asm/mmu_context.h >>>> +++ b/arch/x86/include/asm/mmu_context.h >>>> @@ -343,4 +343,24 @@ static inline unsigned long __get_current_cr3_fas= t(void) >>>> return cr3; >>>> } >>>> >>>> +typedef struct { >>>> + struct mm_struct *prev; >>>> +} temporary_mm_state_t; >>>> + >>>> +static inline temporary_mm_state_t use_temporary_mm(struct mm_struct = *mm) >>>> +{ >>>> + temporary_mm_state_t state; >>>> + >>>> + lockdep_assert_irqs_disabled(); >>>> + state.prev =3D this_cpu_read(cpu_tlbstate.loaded_mm); >>>> + switch_mm_irqs_off(NULL, mm, current); >>>> + return state; >>>> +} >>>> + >>>> +static inline void unuse_temporary_mm(temporary_mm_state_t prev) >>>> +{ >>>> + lockdep_assert_irqs_disabled(); >>>> + switch_mm_irqs_off(NULL, prev.prev, current); >>>> +} >>>> + >>>> #endif /* _ASM_X86_MMU_CONTEXT_H */ >>>> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgt= able.h >>>> index 5715647fc4fe..ef62af9a0ef7 100644 >>>> --- a/arch/x86/include/asm/pgtable.h >>>> +++ b/arch/x86/include/asm/pgtable.h >>>> @@ -976,6 +976,10 @@ static inline void __meminit init_trampoline_defa= ult(void) >>>> /* Default trampoline pgd value */ >>>> trampoline_pgd_entry =3D init_top_pgt[pgd_index(__PAGE_OFFSET)]; >>>> } >>>> + >>>> +void __init patching_mm_init(void); >>>> +#define patching_mm_init patching_mm_init >>>> + >>>> # ifdef CONFIG_RANDOMIZE_MEMORY >>>> void __meminit init_trampoline(void); >>>> # else >>>> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/includ= e/asm/pgtable_64_types.h >>>> index 054765ab2da2..9f44262abde0 100644 >>>> --- a/arch/x86/include/asm/pgtable_64_types.h >>>> +++ b/arch/x86/include/asm/pgtable_64_types.h >>>> @@ -116,6 +116,9 @@ extern unsigned int ptrs_per_p4d; >>>> #define LDT_PGD_ENTRY (pgtable_l5_enabled() ? LDT_PGD_ENTRY_L= 5 : LDT_PGD_ENTRY_L4) >>>> #define LDT_BASE_ADDR (LDT_PGD_ENTRY << PGDIR_SHIFT) >>>> >>>> +#define TEXT_POKE_PGD_ENTRY -5UL >>>> +#define TEXT_POKE_ADDR (TEXT_POKE_PGD_ENTRY << PGDIR_SHIFT) >>>> + >>>> #define __VMALLOC_BASE_L4 0xffffc90000000000UL >>>> #define __VMALLOC_BASE_L5 0xffa0000000000000UL >>>> >>>> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/a= sm/pgtable_types.h >>>> index 99fff853c944..840c72ec8c4f 100644 >>>> --- a/arch/x86/include/asm/pgtable_types.h >>>> +++ b/arch/x86/include/asm/pgtable_types.h >>>> @@ -505,6 +505,9 @@ pgprot_t phys_mem_access_prot(struct file *file, u= nsigned long pfn, >>>> /* Install a pte for a particular vaddr in kernel space. */ >>>> void set_pte_vaddr(unsigned long vaddr, pte_t pte); >>>> >>>> +struct mm_struct; >>>> +void set_mm_pte_vaddr(struct mm_struct *mm, unsigned long vaddr, pte_= t pte); >>>> + >>>> #ifdef CONFIG_X86_32 >>>> extern void native_pagetable_init(void); >>>> #else >>>> diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/a= sm/text-patching.h >>>> index 2ecd34e2d46c..cb364ea5b19d 100644 >>>> --- a/arch/x86/include/asm/text-patching.h >>>> +++ b/arch/x86/include/asm/text-patching.h >>>> @@ -38,4 +38,6 @@ extern void *text_poke(void *addr, const void *opcod= e, size_t len); >>>> extern int poke_int3_handler(struct pt_regs *regs); >>>> extern void *text_poke_bp(void *addr, const void *opcode, size_t len, = void *handler); >>>> >>>> +extern struct mm_struct *patching_mm; >>>> + >>>> #endif /* _ASM_X86_TEXT_PATCHING_H */ >>>> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternati= ve.c >>>> index a481763a3776..fd8a950b0d62 100644 >>>> --- a/arch/x86/kernel/alternative.c >>>> +++ b/arch/x86/kernel/alternative.c >>>> @@ -11,6 +11,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> #include >>>> #include >>>> #include >>>> @@ -701,8 +702,36 @@ void *text_poke(void *addr, const void *opcode, s= ize_t len) >>>> WARN_ON(!PageReserved(pages[0])); >>>> pages[1] =3D virt_to_page(addr + PAGE_SIZE); >>>> } >>>> - BUG_ON(!pages[0]); >>>> + >>>> local_irq_save(flags); >>>> + BUG_ON(!pages[0]); >>>> + >>>> + /* >>>> + * During initial boot, it is hard to initialize patching_mm d= ue to >>>> + * dependencies in boot order. >>>> + */ >>>> + if (patching_mm) { >>>> + pte_t pte; >>>> + temporary_mm_state_t prev; >>>> + >>>> + prev =3D use_temporary_mm(patching_mm); >>>> + pte =3D mk_pte(pages[0], PAGE_KERNEL); >>>> + set_mm_pte_vaddr(patching_mm, TEXT_POKE_ADDR, pte); >>>> + pte =3D mk_pte(pages[1], PAGE_KERNEL); >>>> + set_mm_pte_vaddr(patching_mm, TEXT_POKE_ADDR + PAGE_SI= ZE, pte); >>>> + >>>> + memcpy((void *)(TEXT_POKE_ADDR | ((unsigned long)addr = & ~PAGE_MASK)), >>>> + opcode, len); >>>> + >>>> + set_mm_pte_vaddr(patching_mm, TEXT_POKE_ADDR, __pte(0)= ); >>>> + set_mm_pte_vaddr(patching_mm, TEXT_POKE_ADDR + PAGE_SI= ZE, __pte(0)); >>>> + local_flush_tlb(); >>> >>> Hmm. This is stuff busted on SMP, and it's IMO more complicated than >>> needed. How about getting rid of all the weird TLB flushing stuff and >>> instead putting the mapping at vaddr - __START_KERNEL_map or whatever >>> it is? You *might* need to flush_tlb_mm_range() on module unload, but >>> that's it. >> >> I don=E2=80=99t see what=E2=80=99s wrong in SMP, since this entire piece= of code should be >> running under text_mutex. >> >> I don=E2=80=99t quite understand your proposal. I really don=E2=80=99t w= ant to have any >> chance in which the page-tables for the poked address is not preallocate= d. >> >> It is more complicated than needed, and there are redundant TLB flushes.= The >> reason I preferred to do it this way, is in order not to use other funct= ions >> that take locks during the software page-walk and not to duplicate exist= ing >> code. Yet, duplication might be the way to go. >> >>>> + sync_core(); >>> >>> I can't think of any case where sync_core() is needed. The mm switch >>> serializes. >> >> Good point! >> >>> Also, is there any circumstance in which any of this is used before at >>> least jump table init? All the early stuff is text_poke_early(), >>> right? >> >> Not before jump_label_init. However, I did not manage to get rid of the = two >> code-patches in text_poke(), since text_poke is used relatively early by >> x86_late_time_init(), and at this stage kmem_cache_alloc() - which is ne= eded >> to duplicate init_mm - still fails. > > Another correction: the populate_extra_pte() is not needed. > > Anyhow, if you want to do this whole thing differently, I obviously will = not > object, but I think it will end up more complicated. > > I think I finally understood your comment about "vaddr - > __START_KERNEL_map=E2=80=9D. I did something like that before, and it is = not > super-simple. You need not only to conditionally flush the TLB, but also > to synchronize the PUD/PMD on changes. Don=E2=80=99t forget that module m= emory > is installed even when BPF programs are installed. > > Let me know if you want me to submit cleaner patches or you want to carry= on > yourself. > I think your approach is a good start and should be good enough (with cleanups) as a fix for the bug. But I think your code has the same bug that we have now! You're reusing the same address on multiple CPUs without flushing. You can easily fix it by forcing a flush before loading the mm, which should be as simple as adding flush_tlb_mm() before you load the mm. (It won't actually flush anything by itself, since the mm isn't loaded, but it will update the bookkeeping so that switch_mm_irqs_off() flushes the mm.) Also, please at least get rid of TEXT_POKE_ADDR. If you don't want to do the vaddr - __START_KERNEL_map thing, then at least pick an address in the low half of the address space such as 0 :) Ideally you'd only use this thing late enough that you could even use the normal insert_pfn (or similar) API for it, but that doesn't really matter.