[PATCH AUTOSEL 4.19 188/252] x86/mm: Fix NX bit clearing issue in kernel_map_pages_in_pgd

[Sasha Levin]

From: Ard Biesheuvel <ardb@xxxxxxxxxx>

[ Upstream commit 75fbef0a8b6b4bb19b9a91b5214f846c2dc5139e ]

The following commit:

  15f003d20782 ("x86/mm/pat: Don't implicitly allow _PAGE_RW in kernel_map_pages_in_pgd()")

modified kernel_map_pages_in_pgd() to manage writable permissions
of memory mappings in the EFI page table in a different way, but
in the process, it removed the ability to clear NX attributes from
read-only mappings, by clobbering the clear mask if _PAGE_RW is not
being requested.

Failure to remove the NX attribute from read-only mappings is
unlikely to be a security issue, but it does prevent us from
tightening the permissions in the EFI page tables going forward,
so let's fix it now.

Fixes: 15f003d20782 ("x86/mm/pat: Don't implicitly allow _PAGE_RW in kernel_map_pages_in_pgd()
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200113172245.27925-5-ardb@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/x86/mm/pageattr.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index e2d4b25c7aa44..101f3ad0d6ad1 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -2126,19 +2126,13 @@ int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
 		.pgd = pgd,
 		.numpages = numpages,
 		.mask_set = __pgprot(0),
-		.mask_clr = __pgprot(0),
+		.mask_clr = __pgprot(~page_flags & (_PAGE_NX|_PAGE_RW)),
 		.flags = 0,
 	};
 
 	if (!(__supported_pte_mask & _PAGE_NX))
 		goto out;
 
-	if (!(page_flags & _PAGE_NX))
-		cpa.mask_clr = __pgprot(_PAGE_NX);
-
-	if (!(page_flags & _PAGE_RW))
-		cpa.mask_clr = __pgprot(_PAGE_RW);
-
 	if (!(page_flags & _PAGE_ENC))
 		cpa.mask_clr = pgprot_encrypted(cpa.mask_clr);
 
-- 
2.20.1