Messages in this thread | | | From | Thomas Garnier <> | Date | Thu, 5 Jan 2017 08:40:29 -0800 | Subject | Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location |
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On Thu, Jan 5, 2017 at 7:08 AM, Arjan van de Ven <arjan@linux.intel.com> wrote: > 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() ... >
That seems like a better name.
> one request.. can we make sure this unrandomization is optional? >
Well, it happens only when KASLR memory randomization is enabled. Do you think it should have a separate config option?
-- Thomas
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