linux-kernel - Re: [PATCH 2/2] x86/mm/KASLR: Correct the upper boundary of KALSR mm regions if adjacent to EFI

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Date:   Wed, 8 Mar 2017 14:05:53 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
        linux-efi@...r.kernel.org, thgarnie@...gle.com,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2] x86/mm/KASLR: Correct the upper boundary of KALSR mm
 regions if adjacent to EFI

On Wed, Mar 8, 2017 at 1:48 PM, Dave Young <dyoung@...hat.com> wrote:
> On 03/08/17 at 03:47pm, Baoquan He wrote:
>> EFI allocates runtime services regions top-down, starting from EFI_VA_START
>> to EFI_VA_END. So EFI_VA_START is bigger than EFI_VA_END and is the end of
>> EFI region. The upper boundary of memory regions randomized by KASLR should
>> be EFI_VA_END if it's adjacent to EFI region, but not EFI_VA_START.
>>
>> Correct it in this patch.
>>
>> Signed-off-by: Baoquan He <bhe@...hat.com>
>> ---
>>  arch/x86/mm/kaslr.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
>> index 887e571..aed2064 100644
>> --- a/arch/x86/mm/kaslr.c
>> +++ b/arch/x86/mm/kaslr.c
>> @@ -48,7 +48,7 @@ static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
>>  #if defined(CONFIG_X86_ESPFIX64)
>>  static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
>>  #elif defined(CONFIG_EFI)
>> -static const unsigned long vaddr_end = EFI_VA_START;
>> +static const unsigned long vaddr_end = EFI_VA_END;
>>  #else
>>  static const unsigned long vaddr_end = __START_KERNEL_map;
>>  #endif
>> @@ -105,7 +105,7 @@ void __init kernel_randomize_memory(void)
>>        */
>>       BUILD_BUG_ON(vaddr_start >= vaddr_end);
>>       BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_ESPFIX64) &&
>> -                  vaddr_end >= EFI_VA_START);
>> +                  vaddr_end >= EFI_VA_END);
>>       BUILD_BUG_ON((IS_ENABLED(CONFIG_X86_ESPFIX64) ||
>>                     IS_ENABLED(CONFIG_EFI)) &&
>>                    vaddr_end >= __START_KERNEL_map);
>> --
>> 2.5.5
>>
>
> Acked-by: Dave Young <dyoung@...hat.com>
>

Thanks Bao for this fix. This makes the KASLR code consistent with
Address space markers hints in [1]

[1] http://lxr.free-electrons.com/source/arch/x86/mm/dump_pagetables.c#L82

Reviewed-by: Bhupesh Sharma <bhsharma@...hat.com>

Regards,
Bhupesh