Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC][PATCH v2 11/21] x86/pti: Extend PTI user mappings | Date | Thu, 19 Nov 2020 20:15:54 +0100 |
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On Tue, Nov 17 2020 at 09:42, Alexandre Chartre wrote: > On 11/17/20 12:06 AM, Andy Lutomirski wrote: > The PTI stack does have guard pages because it maps only a part of the task > stack into the user page-table, so pages around the PTI stack are not mapped > into the user-pagetable (the page below is the task stack guard, and the page > above is part of the kernel-only stack so it's never mapped into the user > page-table). > > + * +-------------+ > + * | | ^ ^ > + * | kernel-only | | KERNEL_STACK_SIZE | > + * | stack | | | > + * | | V | > + * +-------------+ <- top of kernel stack | THREAD_SIZE > + * | | ^ | > + * | kernel and | | KERNEL_STACK_SIZE | > + * | PTI stack | | | > + * | | V v > + * +-------------+ <- top of stack
Well, the PTI stack might have guard pages, but the kernel stack can now underflow into the PTI stack. Not good.
Thanks,
tglx
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