On Wed, Sep 08, 2021 at 12:52:45PM +0200, Borislav Petkov wrote:
On Wed, Sep 08, 2021 at 12:35:21PM +0200, Borislav Petkov wrote:
So I did stare at this for a while, trying to make sense of it and David Hildenbrand asked for a Fixes: tag in v1 review and from doing a bit of git archeology I think it should be:
c40a56a7818c ("x86/mm/init: Remove freed kernel image areas from alias mapping")
because that thing added the clearing of the Present bit for the high kernel image mapping of those areas.
Right?
Yes, in a sense. As the only user of kern_addr_valid() is kcore and it only uses this check for high kernel mappings, there should be no problem before 4.19.
But...
Hmm, but that commit is in v4.19. Mike has added
Cc: stable@vger.kernel.org # 4.4+
Mike, why 4.4 and newer?
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...
Hmmm.