lkml.org 
[lkml]   [2017]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 12/30] x86, kaiser: map GDT into user page tables
From
Date
On 11/21/2017 02:46 PM, Andy Lutomirski wrote:
>> GDT: R/O TSS: R/W at least because of trampoline stack entry code:
>> EXEC+R/O exception stacks: R/W
> Can you avoid code duplication by adding some logic right after the
> kernel cpu_entry_area is set up to iterate page by page over the PTEs
> in the cpu_entry_area for that CPU and just install exactly the same
> PTEs into the kaiser table? E.g. just call kaiser_add_mapping once
> per page but with the parameters read out from the fixmap PTEs
> instead of hard coded?

Yes, we could do that. But, what's the gain? We end up removing
effectively three (long) lines of code from three kaiser_add_mapping()
calls.

To do this, we need to special-case the kernel page table walker to deal
with PTEs only since we can't just grab PMD or PUD flags and stick them
in a PTE. We would only be able to use this path when populating things
that we know are 4k-mapped in the kernel.

I guess the upside is that we don't open-code the permissions in the
KAISER code that *have* to match the permissions that the kernel itself
established.

It also means that theoretically you could not touch the KAISER code the
next time we expand the cpu entry area.

\
 
 \ /
  Last update: 2017-11-22 00:18    [W:0.078 / U:13.428 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site