linux-kernel - [PATCH] x86/tdx: Preserve shared bit on mprotect()

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Date: Fri, 12 Apr 2024 22:12:47 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...el.com
Cc: sathyanarayanan.kuppuswamy@...ux.intel.com,
	hpa@...or.com,
	seanjc@...gle.com,
	elena.reshetova@...el.com,
	rick.p.edgecombe@...el.com,
	x86@...nel.org,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Chris Oo <cho@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>
Subject: [PATCH] x86/tdx: Preserve shared bit on mprotect()

The TDX guest platform takes one bit from the physical address to
indicate if the page is shared (accessible by VMM). This bit is not part
of the physical_mask and is not preserved during mprotect(). As a
result, the 'shared' bit is lost during mprotect() on shared mappings.

_COMMON_PAGE_CHG_MASK specifies which PTE bits need to be preserved
during modification. AMD includes 'sme_me_mask' in the define to
preserve the 'encrypt' bit.

To cover both Intel and AMD cases, include 'cc_mask' in
_COMMON_PAGE_CHG_MASK instead of 'sme_me_mask'.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: 41394e33f3a0 ("x86/tdx: Extend the confidential computing API to support TDX guests")
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Chris Oo <cho@...rosoft.com>
Cc: Dexuan Cui <decui@...rosoft.com>
---
 arch/x86/include/asm/pgtable_types.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 3f648ffdfbe5..7dd2fdfacff3 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -148,7 +148,7 @@
 #define _COMMON_PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |	\
 				 _PAGE_SPECIAL | _PAGE_ACCESSED |	\
 				 _PAGE_DIRTY_BITS | _PAGE_SOFT_DIRTY |	\
-				 _PAGE_DEVMAP | _PAGE_ENC | _PAGE_UFFD_WP)
+				 _PAGE_DEVMAP | _PAGE_CC | _PAGE_UFFD_WP)
 #define _PAGE_CHG_MASK	(_COMMON_PAGE_CHG_MASK | _PAGE_PAT)
 #define _HPAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PSE | _PAGE_PAT_LARGE)
 
@@ -173,6 +173,7 @@ enum page_cache_mode {
 };
 #endif
 
+#define _PAGE_CC		(_AT(pteval_t, cc_mask))
 #define _PAGE_ENC		(_AT(pteval_t, sme_me_mask))
 
 #define _PAGE_CACHE_MASK	(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)
-- 
2.43.0