linux-kernel - Re: [PATCH v2 06/18] x86/kasan/64: Teach KASAN about the cpu_entry

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Date:   Thu, 23 Nov 2017 13:08:41 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v2 06/18] x86/kasan/64: Teach KASAN about the
 cpu_entry_area



On 11/22/2017 06:22 PM, Andy Lutomirski wrote:
> On Wed, Nov 22, 2017 at 1:05 AM, Andrey Ryabinin
> <aryabinin@...tuozzo.com> wrote:
>>
>>
>> On 11/22/2017 07:44 AM, Andy Lutomirski wrote:
>>> The cpu_entry_area will contain stacks.  Make sure that KASAN has
>>> appropriate shadow mappings for them.
>>>
>>> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
>>> Cc: Alexander Potapenko <glider@...gle.com>
>>> Cc: Dmitry Vyukov <dvyukov@...gle.com>
>>> Cc: kasan-dev@...glegroups.com
>>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>>> ---
>>>  arch/x86/mm/kasan_init_64.c | 9 ++++++++-
>>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
>>> index 99dfed6dfef8..43d376687315 100644
>>> --- a/arch/x86/mm/kasan_init_64.c
>>> +++ b/arch/x86/mm/kasan_init_64.c
>>> @@ -330,7 +330,14 @@ void __init kasan_init(void)
>>>                             early_pfn_to_nid(__pa(_stext)));
>>>
>>>       kasan_populate_zero_shadow(kasan_mem_to_shadow((void *)MODULES_END),
>>> -                     (void *)KASAN_SHADOW_END);
>>> +                                kasan_mem_to_shadow((void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM))));
>>> +
>>> +     kasan_populate_shadow((unsigned long)kasan_mem_to_shadow((void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM))),
>>> +                           (unsigned long)kasan_mem_to_shadow((void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_TOP) + PAGE_SIZE)),
>>
>> What's '+ PAGE_SIZE' for?
>>
> 
> __fix_to_virt(..._TOP) returns the address of the *bottom* of the last
> cpu_entry_area page.  +PAGE_SIZE returns one past the end of the
> region, which I assume is the correct thing to pass.
> 

Right.

Perhaps, it would be better to use variables, just avoid such awfully long lines, I mean like this:
	fixmap_shadow_start = (void *)__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM);
	fixmap_shadow_start = kasan_mem_to_shadow(fixmap_shadow_start);

	fixmap_shadow_end = (void *)__fix_to_virt(FIX_CPU_ENTRY_AREA_TOP) + PAGE_SIZE;
	fixmap_shadow_end = kasan_mem_to_shadow(fixmap_shadow_end);

	kasan_populate_zero_shadow(kasan_mem_to_shadow((void *)MODULES_END),
				   fixmap_shadow_start);

	kasan_populate_shadow((unsigned long)fixmap_shadow_start,
			(unsigned long)fixmap_shadow_end,
			0);

I'm also thinking that we should change kasan_populate_shadow() to take void* instead of 'unsigned long'
to avoid those casts.