linux-kernel - [tip: x86/mm] x86: Don't let pgprot_modify() change the page encryption bit

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Date:   Tue, 17 Mar 2020 14:57:21 -0000
From:   "tip-bot2 for Thomas Hellstrom" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Hellstrom <thellstrom@...are.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/mm] x86: Don't let pgprot_modify() change the page encryption bit

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     6db73f17c5f155dbcfd5e48e621c706270b84df0
Gitweb:        https://git.kernel.org/tip/6db73f17c5f155dbcfd5e48e621c706270b84df0
Author:        Thomas Hellstrom <thellstrom@...are.com>
AuthorDate:    Wed, 04 Mar 2020 12:45:26 +01:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Tue, 17 Mar 2020 11:48:31 +01:00

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@...are.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
Acked-by: Tom Lendacky <thomas.lendacky@....com>
Link: https://lkml.kernel.org/r/20200304114527.3636-2-thomas_os@shipmail.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 7e11866..64a03f2 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 0239998..65c2ecd 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)
 
 /*