Re: 4.4-rc5: ugly warn on: 5 W+X pages found

[Borislav Petkov <bp@alien8.de>]

On Tue, Dec 15, 2015 at 09:45:40AM -0800, Linus Torvalds wrote:
> On Tue, Dec 15, 2015 at 1:40 AM, Pavel Machek <pavel@ucw.cz> wrote:
> >
> > I tried applying:
> >
> > [PATCH 1/2] x86_32/mm: Set NX in __supported_pte_mask before enabling
> > paging
> >
> > but I still get
> >
> > [    2.691897] x86/mm: Found insecure W+X mapping at address ffe69000/0xffe69000
> 
> This may be an insane suggestion, but how about we try to detect when
> that entry gets set, rather than after the fact.
> 
> Something really brute-force like
> 
>   diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
>   index 6ec0c8b2e9df..538c9bb239b9 100644
>   --- a/arch/x86/include/asm/pgtable.h
>   +++ b/arch/x86/include/asm/pgtable.h
>   @@ -337,6 +337,13 @@ static inline pmd_t pmd_clear_soft_dirty(pmd_t pmd)
> 
>    #endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */
> 
>   +static inline int kernel_write_execute_prot(pgprotval_t protval)
>   +{
>   +       return !(protval & _PAGE_USER) &&
>   +               !(protval & _PAGE_NX) &&

Shouldn't this be without a "!"? AFAIU, we want _PAGE_NX | _PAGE_RW?

-- 
Regards/Gruss,
    Boris.

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