[PATCH 4.9 014/138] ARM: 8722/1: mm: make STRICT_KERNEL_RWX effective for LPAE

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Philip Derrin <philip@xxxxxxxxxxx>

commit 400eeffaffc7232c0ae1134fe04e14ae4fb48d8c upstream.

Currently, for ARM kernels with CONFIG_ARM_LPAE and
CONFIG_STRICT_KERNEL_RWX enabled, the 2MiB pages mapping the
kernel code and rodata are writable. They are marked read-only in
a software bit (L_PMD_SECT_RDONLY) but the hardware read-only bit
is not set (PMD_SECT_AP2).

For user mappings, the logic that propagates the software bit
to the hardware bit is in set_pmd_at(); but for the kernel,
section_update() writes the PMDs directly, skipping this logic.

The fix is to set PMD_SECT_AP2 for read-only sections in
section_update(), at the same time as L_PMD_SECT_RDONLY.

Fixes: 1e3479225acb ("ARM: 8275/1: mm: fix PMD_SECT_RDONLY undeclared compile error")
Signed-off-by: Philip Derrin <philip@xxxxxxxxxxx>
Reported-by: Neil Dick <neil@xxxxxxxxxxx>
Tested-by: Neil Dick <neil@xxxxxxxxxxx>
Tested-by: Laura Abbott <labbott@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arm/mm/init.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -619,8 +619,8 @@ static struct section_perm ro_perms[] =
 		.start  = (unsigned long)_stext,
 		.end    = (unsigned long)__init_begin,
 #ifdef CONFIG_ARM_LPAE
-		.mask   = ~L_PMD_SECT_RDONLY,
-		.prot   = L_PMD_SECT_RDONLY,
+		.mask   = ~(L_PMD_SECT_RDONLY | PMD_SECT_AP2),
+		.prot   = L_PMD_SECT_RDONLY | PMD_SECT_AP2,
 #else
 		.mask   = ~(PMD_SECT_APX | PMD_SECT_AP_WRITE),
 		.prot   = PMD_SECT_APX | PMD_SECT_AP_WRITE,