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Tue, 28 Aug 2018 10:33:05 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) Subject: Re: TLB flushes on fixmap changes From: Nadav Amit In-Reply-To: <20180828174948.dc0474009be1ec7a0392cfcd@kernel.org> Date: Tue, 28 Aug 2018 10:33:02 -0700 Cc: 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-Transfer-Encoding: quoted-printable Message-Id: <7F3235AF-5300-49B6-A9A4-C8BA8EF1D87B@gmail.com> References: <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> <2998E63A-5663-4805-9DE7-829A5870AA6D@gmail.com> <20180828174948.dc0474009be1ec7a0392cfcd@kernel.org> To: Masami Hiramatsu , Andy Lutomirski X-Mailer: Apple Mail (2.3445.9.1) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org at 1:49 AM, Masami Hiramatsu wrote: > On Mon, 27 Aug 2018 16:01:32 -0700 > Andy Lutomirski wrote: >=20 >> On Mon, Aug 27, 2018 at 3:54 PM, Nadav Amit = wrote: >>> at 3:32 PM, Andy Lutomirski wrote: >>>=20 >>>> On Mon, Aug 27, 2018 at 2:55 PM, Nadav Amit = wrote: >>>>> at 1:16 PM, Nadav Amit wrote: >>>>>=20 >>>>>> at 12:58 PM, Andy Lutomirski wrote: >>>>>>=20 >>>>>>> On Mon, Aug 27, 2018 at 12:43 PM, Nadav Amit = wrote: >>>>>>>> at 12:10 PM, Nadav Amit wrote: >>>>>>>>=20 >>>>>>>>> at 11:58 AM, Andy Lutomirski wrote: >>>>>>>>>=20 >>>>>>>>>> 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? >>>>>>>>>>>=20 >>>>>>>>>>> I agree in general. But I think that current->mm would need = to be loaded, as >>>>>>>>>>> otherwise I am afraid it would break switch_mm_irqs_off(). >>>>>>>>>>=20 >>>>>>>>>> What breaks? >>>>>>>>>=20 >>>>>>>>> Actually nothing. I just saw the IBPB stuff regarding tsk, but = it should not >>>>>>>>> matter. >>>>>>>>=20 >>>>>>>> So here is what I got. It certainly needs some cleanup, but it = boots. >>>>>>>>=20 >>>>>>>> Let me know how crappy you find it... >>>>>>>>=20 >>>>>>>>=20 >>>>>>>> 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_fast(void) >>>>>>>> return cr3; >>>>>>>> } >>>>>>>>=20 >>>>>>>> +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/pgtable.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_default(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/include/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_L5 : LDT_PGD_ENTRY_L4) >>>>>>>> #define LDT_BASE_ADDR (LDT_PGD_ENTRY << PGDIR_SHIFT) >>>>>>>>=20 >>>>>>>> +#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 >>>>>>>>=20 >>>>>>>> diff --git a/arch/x86/include/asm/pgtable_types.h = b/arch/x86/include/asm/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, unsigned long pfn, >>>>>>>> /* Install a pte for a particular vaddr in kernel space. */ >>>>>>>> void set_pte_vaddr(unsigned long vaddr, pte_t pte); >>>>>>>>=20 >>>>>>>> +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/asm/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 = *opcode, 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); >>>>>>>>=20 >>>>>>>> +extern struct mm_struct *patching_mm; >>>>>>>> + >>>>>>>> #endif /* _ASM_X86_TEXT_PATCHING_H */ >>>>>>>> diff --git a/arch/x86/kernel/alternative.c = b/arch/x86/kernel/alternative.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, size_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 due 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_SIZE, 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_SIZE, __pte(0)); >>>>>>>> + local_flush_tlb(); >>>>>>>=20 >>>>>>> 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. >>>>>>=20 >>>>>> 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. >>>>>>=20 >>>>>> I don=E2=80=99t quite understand your proposal. I really don=E2=80=99= t want to have any >>>>>> chance in which the page-tables for the poked address is not = preallocated. >>>>>>=20 >>>>>> 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 functions >>>>>> that take locks during the software page-walk and not to = duplicate existing >>>>>> code. Yet, duplication might be the way to go. >>>>>>=20 >>>>>>>> + sync_core(); >>>>>>>=20 >>>>>>> I can't think of any case where sync_core() is needed. The mm = switch >>>>>>> serializes. >>>>>>=20 >>>>>> Good point! >>>>>>=20 >>>>>>> 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? >>>>>>=20 >>>>>> 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 needed >>>>>> to duplicate init_mm - still fails. >>>>>=20 >>>>> Another correction: the populate_extra_pte() is not needed. >>>>>=20 >>>>> Anyhow, if you want to do this whole thing differently, I = obviously will not >>>>> object, but I think it will end up more complicated. >>>>>=20 >>>>> 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 memory >>>>> is installed even when BPF programs are installed. >>>>>=20 >>>>> Let me know if you want me to submit cleaner patches or you want = to carry on >>>>> yourself. >>>>=20 >>>> 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.) >>>=20 >>> What am I missing? >>>=20 >>> We have a lock (text_mutex) which prevents the use of the new = page-table >>> hierarchy on multiple CPUs. In addition we have __set_pte_vaddr() = which does >>> a local TLB flush before the lock is released and before IRQs are = enabled. >>> So how can the PTE be cached on multiple CPUs? >>>=20 >>> Yes, __set_pte_vaddr() is ugly and flushes too much. I=E2=80=99ll = try to remove some >>> redundant TLB flushes, but these flushes are already there. >>=20 >> I missed that set_pte_vaddr() contained a flush. It's probably nicer >> to use one of the APIs that doesn't imply a flush. If you end up = with >> vm_insert_pfn() or similar, you can use can use copy_to_user() if >> needed :) >>=20 >>>> 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. >>>=20 >>> Perhaps the vaddr - __START_KERNEL_map actually makes sense. I was >>> misunderstanding it (again) before, thinking you want me to use = vaddr (and >>> not the delta). I=E2=80=99ll give it a try. >>=20 >> It does prevent easy preallocation of the intermediate tables. >=20 > Would we have to change the mapping address? If so, how about using = hash > of vaddr, which allow us to map it in one pte? We do need two PTEs, and I will reuse the same two PTEs in order not to waste memory on page-tables. I will try to randomize their address to be = on the safe side.