Re: [PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is used inappropriately

[Borislav Petkov <bp@alien8.de>]

On Fri, Jun 17, 2016 at 01:00:39PM -0700, Andy Lutomirski wrote:
> It's currently only used in the EFI code, which is safe AFAICT.

"It is basically useful for a pagetable hierarchy which is not init_mm."

> Warn if anyone tries to use it on the normal kernel pgd.
> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/x86/mm/pageattr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 6a8026918bf6..e9b9c5cedbb8 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -1996,6 +1996,9 @@ out:
>  void kernel_unmap_pages_in_pgd(pgd_t *root, unsigned long address,
>  			       unsigned numpages)
>  {
> +	/* Unmapping kernel entries from init_mm's pgd is not allowed. */
> +	WARN_ON(root == init_mm.pgd);

We can also return and not do the unmapping:

	if (WARN_ON(root == init_mm.pgd))
		return;

-- 
Regards/Gruss,
    Boris.

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