linux-kernel - [PATCH 4.9 11/97] arm64: Make sure permission updates happen for pmd/pud

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Date:   Wed, 22 Jan 2020 10:28:15 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Peter Robinson <pbrobinson@...il.com>,
        Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>
Subject: [PATCH 4.9 11/97] arm64: Make sure permission updates happen for pmd/pud

From: Laura Abbott <labbott@...hat.com>

commit 82034c23fcbc2389c73d97737f61fa2dd6526413 upstream.

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@...omium.org>
Tested-by: Peter Robinson <pbrobinson@...il.com>
Reported-by: Peter Robinson <pbrobinson@...il.com>
Fixes: 15122ee2c515 ("arm64: Enforce BBM for huge IO/VMAP mappings")
Signed-off-by: Laura Abbott <labbott@...hat.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/mm/mmu.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -799,13 +799,15 @@ int pud_set_huge(pud_t *pudp, phys_addr_
 {
 	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;
 }
 
@@ -813,13 +815,15 @@ int pmd_set_huge(pmd_t *pmdp, phys_addr_
 {
 	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;
 }