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Subject[PATCH 4.4 11/96] ARM: 8722/1: mm: make STRICT_KERNEL_RWX effective for LPAE
4.4-stable review patch.  If anyone has any objections, please let me know.


From: Philip Derrin <>

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 <>
Reported-by: Neil Dick <>
Tested-by: Neil Dick <>
Tested-by: Laura Abbott <>
Reviewed-by: Kees Cook <>
Signed-off-by: Russell King <>
Signed-off-by: Greg Kroah-Hartman <>

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
@@ -611,8 +611,8 @@ static struct section_perm ro_perms[] =
.start = (unsigned long)_stext,
.end = (unsigned long)__init_begin,
- .mask = ~L_PMD_SECT_RDONLY,
- .prot = L_PMD_SECT_RDONLY,
+ .mask = ~(L_PMD_SECT_RDONLY | PMD_SECT_AP2),

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