[PATCH AUTOSEL 4.19 08/32] x86: Don't let pgprot_modify() change the page encryption bit

[Sasha Levin]

From: Thomas Hellstrom <thellstrom@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Link: https://lkml.kernel.org/r/20200304114527.3636-2-thomas_os@xxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@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 690c0307afed0..2e1ed12c65f82 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -608,12 +608,15 @@ 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 106b7d0e2dae5..71ea49e7db747 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -124,7 +124,7 @@
  */
 #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