RW and executable hole in page tables on x86_64

[Kees Cook]

Hi,

I've noticed there's a chunk of kernel memory still marked RW and x. See
0xffffffff82956000 below...

---[ High Kernel Mapping ]---
0xffffffff80000000-0xffffffff81000000          16M                           pmd
0xffffffff81000000-0xffffffff81a00000          10M     ro         PSE GLB x  pmd
0xffffffff81a00000-0xffffffff81e00000           4M     ro         PSE GLB NX pmd
0xffffffff81e00000-0xffffffff82200000           4M     RW             GLB NX pte
0xffffffff82200000-0xffffffff82800000           6M     RW         PSE GLB NX pmd
0xffffffff82800000-0xffffffff82956000        1368K     RW             GLB NX pte
0xffffffff82956000-0xffffffff82a00000         680K     RW             GLB x  pte
0xffffffff82a00000-0xffffffffa0000000         470M                           pmd

HPA looked at it for a bit, but it wasn't obvious what was going on. It's
after the end of bss. I do note that the two adjacent regions add up to
2MiB. Is this some kind of leftover mapping? What is this region? Is there
a sensible place to clean it up?

Thanks,

-Kees

-- 
Kees Cook                                            @outflux.net
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