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

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Date:   Wed, 22 Nov 2017 07:22:28 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Andy Lutomirski <luto@...nel.org>, 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 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.