x86: Don't let pgprot_modify() change the page encryption bit

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

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 7e118660bbd9840538ab26f90e9a3fe3d768b8e4..64a03f226ab733e6d43502280caa43c25ca6d5ba 100644 (file)
--- 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 0239998d8cdc04b0d2c3693e59b0bd4f7a5c9025..65c2ecd730c5b6db6b7481d20255f9dbeda2dcb3 100644 (file)
--- 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)
 
 /*