4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Philip Derrin <philip@cog.systems>
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@cog.systems>
Reported-by: Neil Dick <neil@cog.systems>
Tested-by: Neil Dick <neil@cog.systems>
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
@@ -639,8 +639,8 @@ 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,