x86/mm: Fix NX bit clearing issue in kernel_map_pages_in_pgd

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@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200113172245.27925-5-ardb@kernel.org

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 20823392f4f256c9ed731c5266073431e30deec2..62a8ebe72a52f817f1aa3ea24ae04937c9d6301b 100644 (file)
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2215,7 +2215,7 @@ int __init 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,
        };
 
@@ -2224,12 +2224,6 @@ int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
        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);