Re: [PATCH v2] x86/mm: fix kern_addr_valid to cope with existing but not present entries

[Borislav Petkov]

On Wed, Sep 08, 2021 at 02:22:31PM +0300, Mike Rapoport wrote:
> kern_addr_valid() wrongly uses pxy_none() rather than pxy_present() because
> according to 9a14aefc1d28 ("x86: cpa, fix lookup_address") there could be
> cases when page table entries exist but they are not valid.
> So a call to kern_addr_valid() for an address in the direct map would oops.
> 
> I've stopped digging at 9a14aefc1d28 (which is in v2.6.26) and added the
> oldest stable we still support (4.4).
> 
> I agree that before 4.19 it's more of a theoretical bug, but you know,
> things happen...

Hmmkay, I guess I should add the gist of that to the commit message so
that it is explained why 4.4.

I'm assuming the pxy_present() check is more strict than pxy_none() so
that backporting to all stable kernels should not introduce any risks...

-- 
Regards/Gruss,
    Boris.

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