Re: [PATCH v2 1/2] x86: Don't let pgprot_modify() change the page encryption bit

[Thomas HellstrÃm (VMware)]

On 9/11/19 3:27 PM, Lendacky, Thomas wrote:
> On 9/11/19 7:40 AM, Thomas HellstrÃm (VMware) wrote:
> > From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> >
> > When SEV or SME is enabled and active, vm_get_page_prot() typically
> > returns with the encryption bit set. This means that users of
> > pgprot_modify(, vm_get_page_prot()) (mprotect_fixup, do_mmap) end up with
> > a value of vma->vm_pg_prot that is not consistent with the intended
> > protection of the PTEs. This is also important for fault handlers that
> > rely on the VMA vm_page_prot to set the page protection. Fix this by
> > not allowing pgprot_modify() to change the encryption bit, similar to
> > how it's done for PAT bits.
> >
> > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> > Cc: Christian KÃnig <christian.koenig@xxxxxxx>
> > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/pgtable.h       | 7 +++++--
> >   arch/x86/include/asm/pgtable_types.h | 2 +-
> >   2 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> > index 0bc530c4eb13..1e6bb4c25334 100644
> > --- a/arch/x86/include/asm/pgtable.h
> > +++ b/arch/x86/include/asm/pgtable.h
> > @@ -624,12 +624,15 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
> >   	return __pmd(val);
> >   }
> >   
> > -/* mprotect needs to preserve PAT bits when updating vm_page_prot */
> > +/*
> > + * mprotect needs to preserve PAT and encryption bits when updating
> > + * vm_page_prot
> > + */
> >   #define pgprot_modify pgprot_modify
> >   static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
> >   {
> >   	pgprotval_t preservebits = pgprot_val(oldprot) & _PAGE_CHG_MASK;
> > -	pgprotval_t addbits = pgprot_val(newprot);
> > +	pgprotval_t addbits = pgprot_val(newprot) & ~_PAGE_CHG_MASK;
> >   	return __pgprot(preservebits | addbits);
> >   }
> >   
> > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> > index b5e49e6bac63..e13084b3d6cb 100644
> > --- a/arch/x86/include/asm/pgtable_types.h
> > +++ b/arch/x86/include/asm/pgtable_types.h
> > @@ -123,7 +123,7 @@
> >    */
> >   #define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
> >   			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
> > -			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
> > +			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP | sme_me_mask)
> There is a _PAGE_ENC definition that you could use to make this more
> consistent with the current definition.

Ah yes.

I'll wait a bit to see if there are more concerns and include this in 
the next version.

Thanks,

Thomas



> Thanks,
> Tom
>
> >   #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
> >   
> >   /*