Messages in this thread | | | Date | Tue, 17 Aug 2021 22:24:47 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v28 09/32] x86/mm: Introduce _PAGE_COW |
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On Tue, Aug 17, 2021 at 01:13:09PM -0700, Andy Lutomirski wrote: > > If special kernel code using shadow stack management insns needs > > to modify a shadow stack, then it can check whether a page is > > pte/pmd_shstk() but that code is special anyway. > > > > Hell, a shadow stack page is (Write=0, Dirty=1) so calling it writable > > ^^^^^^^ > > is simply wrong. > > But it *is* writable using WRUSS, and it’s also writable by CALL,
Well, if we have to be precise, CALL doesn't write it directly - it causes for shadow stack to be written as part of CALL's execution. Yeah yeah, potato potato.
> WRSS, etc.
Thus the "special kernel code" thing above. I've left it in instead of snipping it.
> Now if the mm code tries to write protect it and expects sensible > semantics, the results could be interesting. At the very least, > someone would need to validate that RET reading a read only shadow > stack page does the right thing.
Huh?
A shadow stack page is RO (W=0).
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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