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SubjectRe: [RFC] x86/mm/KASLR: Remap GDTs at fixed location
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On 1/5/2017 12:11 AM, Ingo Molnar wrote:
>
> * Thomas Garnier <thgarnie@google.com> wrote:
>
>> Each processor holds a GDT in its per-cpu structure. The sgdt
>> instruction gives the base address of the current GDT. This address can
>> be used to bypass KASLR memory randomization. With another bug, an
>> attacker could target other per-cpu structures or deduce the base of the
>> main memory section (PAGE_OFFSET).
>>
>> In this change, a space is reserved at the end of the memory range
>> available for KASLR memory randomization. The space is big enough to hold
>> the maximum number of CPUs (as defined by setup_max_cpus). Each GDT is
>> mapped at specific offset based on the target CPU. Note that if there is
>> not enough space available, the GDTs are not remapped.
>>
>> The document was changed to mention GDT remapping for KASLR. This patch
>> also include dump page tables support.
>>
>> This patch was tested on multiple hardware configurations and for
>> hibernation support.
>
>> void kernel_randomize_memory(void);
>> +void kernel_randomize_smp(void);
>> +void* kaslr_get_gdt_remap(int cpu);
>
> Yeah, no fundamental objections from me to the principle, but I get some bad vibes
> from the naming here: seeing that kernel_randomize_smp() actually makes things
> less random.
>

kernel_unrandomize_smp() ...

one request.. can we make sure this unrandomization is optional?

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