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From: Andrey Ryabinin <aryabinin@virtuozzo.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, Borislav Petkov <bpetkov@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH v3 05/19] x86/kasan/64: Teach KASAN about the cpu_entry_area
Date: Fri, 24 Nov 2017 20:26:06 +0300
Message-ID: <7a9aa9dd-8c9b-d0c2-9b13-d8fe06f48722@virtuozzo.com> (raw)
In-Reply-To: <CALCETrW7=WDxt_ZiXKBez9mTGz92qeVxWJp3BJauEtAs3r4cTg@mail.gmail.com>

On 11/24/2017 07:27 PM, Andy Lutomirski wrote:

>>> +     cpu_entry_area_begin = (void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM));
>>> +     cpu_entry_area_end = (void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_TOP) + PAGE_SIZE);
>>> +
>>>       kasan_populate_zero_shadow(kasan_mem_to_shadow((void *)MODULES_END),
>>> -                     (void *)KASAN_SHADOW_END);
>>> +                                kasan_mem_to_shadow(cpu_entry_area_begin));
>>> +
>>> +     kasan_populate_shadow((unsigned long)kasan_mem_to_shadow(cpu_entry_area_begin),
>>> +                           (unsigned long)kasan_mem_to_shadow(cpu_entry_area_end),
>>> +             0);
>>> +
>>> +     kasan_populate_zero_shadow(kasan_mem_to_shadow(cpu_entry_area_end),
>>
>> Seems we need to round_up kasan_mem_to_shadow(cpu_entry_area_end) to the next page
>> (or alternatively - round_up(cpu_entry_area_end, KASAN_SHADOW_SCALE_SIZE*PAGE_SIZE)).
>> Otherwise, kasan_populate_zero_shadow() will overpopulate the last shadow page of cpu_entry area with kasan_zero_page.
>>
>> We don't necessarily need to round_down(kasan_mem_to_shadow(cpu_entry_area_begin), PAGE_SIZE) because
>> kasan_populate_zero_shadow() will not populate the last 'incomplete' page and kasan_populate_shadow()
>> does round_down() internally, which is exactly what we want here. But it might be better to round_down()
>> explicitly anyway, to avoid relying on such subtle implementation details.
> 
> Any chance you could send a fixup patch or a replacement patch?  You
> obviously understand this code *way* better than I do.
> 
> Or you could do my table-based approach and fix it permanently... :)
> 

Perhaps I'll look at table-based approach later. I've send you a fixed patch for now, to not slow you down.

  parent reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-24  4:32 [PATCH v3 00/19] Entry stack switching Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 01/19] x86/asm/64: Allocate and enable the SYSENTER stack Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 02/19] x86/dumpstack: Add get_stack_info() support for " Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 03/19] x86/gdt: Put per-cpu GDT remaps in ascending order Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 04/19] x86/fixmap: Generalize the GDT fixmap mechanism Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 05/19] x86/kasan/64: Teach KASAN about the cpu_entry_area Andy Lutomirski
2017-11-24 13:16   ` Andrey Ryabinin
2017-11-24 16:27     ` Andy Lutomirski
2017-11-24 17:21       ` [PATCH v4] x86/mm/kasan: " Andrey Ryabinin
2017-11-24 19:26         ` Andy Lutomirski
2017-11-24 17:26       ` Andrey Ryabinin [this message]
2017-11-24  4:32 ` [PATCH v3 06/19] x86/asm: Fix assumptions that the HW TSS is at the beginning of cpu_tss Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 07/19] x86/dumpstack: Handle stack overflow on all stacks Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 08/19] x86/asm: Move SYSENTER_stack to the beginning of struct tss_struct Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 09/19] x86/asm: Remap the TSS into the cpu entry area Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 10/19] x86/asm/64: Separate cpu_current_top_of_stack from TSS.sp0 Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 11/19] x86/espfix/64: Stop assuming that pt_regs is on the entry stack Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 12/19] x86/asm/64: Use a percpu trampoline stack for IDT entries Andy Lutomirski
2017-11-24  4:32 ` [PATCH v3 13/19] x86/asm/64: Return to userspace from the trampoline stack Andy Lutomirski
2017-11-24  4:33 ` [PATCH v3 14/19] x86/entry/64: Create a percpu SYSCALL entry trampoline Andy Lutomirski
2017-11-24 11:39   ` David Laight
2017-12-01  5:56     ` Andy Lutomirski
2017-11-24  4:33 ` [PATCH v3 15/19] x86/irq: Remove an old outdated comment about context tracking races Andy Lutomirski
2017-11-24  4:33 ` [PATCH v3 16/19] x86/irq/64: In the stack overflow warning, print the offending IP Andy Lutomirski
2017-11-24  4:33 ` [PATCH v3 17/19] x86/entry/64: Move the IST stacks into cpu_entry_area Andy Lutomirski
2017-11-24  4:33 ` [PATCH v3 18/19] x86/entry/64: Remove the SYSENTER stack canary Andy Lutomirski
2017-11-24  4:33 ` [PATCH v3 19/19] x86/entry: Clean up SYSENTER_stack code Andy Lutomirski

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