arm64: Make sure permission updates happen for pmd/pud

Commit 15122ee2c515 ("arm64: Enforce BBM for huge IO/VMAP mappings")
disallowed block mappings for ioremap since that code does not honor
break-before-make. The same APIs are also used for permission updating
though and the extra checks prevent the permission updates from happening,
even though this should be permitted. This results in read-only permissions
not being fully applied. Visibly, this can occasionaly be seen as a failure
on the built in rodata test when the test data ends up in a section or
as an odd RW gap on the page table dump. Fix this by using
pgattr_change_is_safe instead of p*d_present for determining if the
change is permitted.

Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Reported-by: Peter Robinson <pbrobinson@gmail.com>
Fixes: 15122ee2c515 ("arm64: Enforce BBM for huge IO/VMAP mappings")
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 2dbb2c9f1ec1770e7f9f5aca7176eac2cc153d32..493ff75670ffd98a1dc344a133f0f31a634f93ff 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -933,13 +933,15 @@ int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)
 {
        pgprot_t sect_prot = __pgprot(PUD_TYPE_SECT |
                                        pgprot_val(mk_sect_prot(prot)));
+       pud_t new_pud = pfn_pud(__phys_to_pfn(phys), sect_prot);
 
-       /* ioremap_page_range doesn't honour BBM */
-       if (pud_present(READ_ONCE(*pudp)))
+       /* Only allow permission changes for now */
+       if (!pgattr_change_is_safe(READ_ONCE(pud_val(*pudp)),
+                                  pud_val(new_pud)))
                return 0;
 
        BUG_ON(phys & ~PUD_MASK);
-       set_pud(pudp, pfn_pud(__phys_to_pfn(phys), sect_prot));
+       set_pud(pudp, new_pud);
        return 1;
 }
 
@@ -947,13 +949,15 @@ int pmd_set_huge(pmd_t *pmdp, phys_addr_t phys, pgprot_t prot)
 {
        pgprot_t sect_prot = __pgprot(PMD_TYPE_SECT |
                                        pgprot_val(mk_sect_prot(prot)));
+       pmd_t new_pmd = pfn_pmd(__phys_to_pfn(phys), sect_prot);
 
-       /* ioremap_page_range doesn't honour BBM */
-       if (pmd_present(READ_ONCE(*pmdp)))
+       /* Only allow permission changes for now */
+       if (!pgattr_change_is_safe(READ_ONCE(pmd_val(*pmdp)),
+                                  pmd_val(new_pmd)))
                return 0;
 
        BUG_ON(phys & ~PMD_MASK);
-       set_pmd(pmdp, pfn_pmd(__phys_to_pfn(phys), sect_prot));
+       set_pmd(pmdp, new_pmd);
        return 1;
 }