Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

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On 9/9/2020 4:11 PM, Dave Hansen wrote:
On 9/9/20 4:07 PM, Yu, Yu-cheng wrote:
What if a writable mapping is passed to madvise(MADV_SHSTK)?  Should
that be rejected?

It doesn't matter to me.  Even if it's readable, it _stops_ being even
directly readable after it's a shadow stack, right?  I don't think
writes are special in any way.  If anything, we *want* it to be writable
because that indicates that it can be written to, and we will want to
write to it soon.

But in a PROT_WRITE mapping, all the pte's have _PAGE_BIT_RW set. To change them to shadow stack, we need to clear that bit from the pte's.
That will be like mprotect_fixup()/change_protection_range().




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