[PATCH AUTOSEL 5.6 27/68] x86: Don't let pgprot_modify() change the page encryption bit

Sasha Levin
2020-04-10T03:47:13Z

From: Thomas Hellstrom <thellstrom@vmware.com>

[ Upstream commit 6db73f17c5f155dbcfd5e48e621c706270b84df0 ]

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.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lkml.kernel.org/r/20200304114527.3636-2-thomas_os@shipmail.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 7e118660bbd98..64a03f226ab73 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -627,12 +627,15 @@ 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 0239998d8cdc0..65c2ecd730c5b 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -118,7 +118,7 @@
*/
#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 | _PAGE_ENC)
#define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)

/*
--
2.20.1