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

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is used inappropriately
Date	2016-06-18 12:30 +0200
Message-ID	<rLlFM-2MV-31@gated-at.bofh.it> (permalink)
References	<rL8fv-2Ds-3@gated-at.bofh.it> <rL8fv-2Ds-17@gated-at.bofh.it> <rL8Ix-2Uy-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Fri, Jun 17, 2016 at 1:30 PM, Borislav Petkov <bp@alien8.de> wrote:
> 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;

I'll do one better: the only function that calls this function is
unused.  I'll just delete it.

--Andy

Thread

[PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is used inappropriately Andy Lutomirski <luto@kernel.org> - 2016-06-17 22:10 +0200
  Re: [PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is  used inappropriately Borislav Petkov <bp@alien8.de> - 2016-06-17 22:40 +0200
    Re: [PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is  used inappropriately Andy Lutomirski <luto@amacapital.net> - 2016-06-18 12:30 +0200
      Re: [PATCH v2 03/13] x86/cpa: Warn if kernel_unmap_pages_in_pgd is  used inappropriately Borislav Petkov <bp@alien8.de> - 2016-06-18 12:40 +0200

csiph-web