Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)

Jiri Kosina
2018-01-05T19:17:22Z

On Fri, 5 Jan 2018, Dave Hansen wrote:

> > --- a/arch/x86/platform/efi/efi_64.c
> > +++ b/arch/x86/platform/efi/efi_64.c
> > @@ -95,6 +95,12 @@ pgd_t * __init efi_call_phys_prolog(void
> > save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE);
> > vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
> > set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
> > + /*
> > + * pgprot API doesn't clear it for PGD
> > + *
> > + * Will be brought back automatically in _epilog()
> > + */
> > + pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX;
> > }
> > __flush_tlb_all();
>
> Wait a sec... Where does the _PAGE_USER come from? Shouldn't we see
> the &init_mm in there and *not* set _PAGE_USER?

That's because pgd_populate() uses _PAGE_TABLE and not _KERNPG_TABLE for
reasons that are behind me.

I did put this on my TODO list, but for later.

(and yes, I tried clearing _PAGE_USER from init_mm's PGD, and no obvious
breakages appeared, but I wanted to give it more thought later).

--
Jiri Kosina
SUSE Labs