Re: [patch 56/60] x86/mm/kpti: Disable native VSYSCALL

[Andy Lutomirski]

On Mon, Dec 4, 2017 at 6:08 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> The KERNEL_PAGE_TABLE_ISOLATION code attempts to "poison" the user
> portion of the kernel page tables. It detects entries that it wants that it
> wants to poison in two ways:
>
>  * Looking for addresses >= PAGE_OFFSET
>
>  * Looking for entries without _PAGE_USER set
>
> But, to allow the _PAGE_USER check to work, it must never be set on
> init_mm entries, and an earlier patch in this series ensured that it
> will never be set.
>
> The VDSO is at a address >= PAGE_OFFSET and it is also mapped by init_mm.
> Because of the earlier, KERNEL_PAGE_TABLE_ISOLATION-enforced restriction,
> _PAGE_USER is never set which makes the VDSO unreadable to userspace.
>
> This makes the "NATIVE" case totally unusable since userspace can not even
> see the memory any more.  Disable it whenever KERNEL_PAGE_TABLE_ISOLATION
> is enabled.
>
> Also add some help text about how KERNEL_PAGE_TABLE_ISOLATION might
> affect the emulation case as well.
>

I think my other suggestion may obsolete this patch.