ARM: mm: allow non-text sections to be non-executable
Adds CONFIG_ARM_KERNMEM_PERMS to separate the kernel memory regions
into section-sized areas that can have different permisions. Performs
the NX permission changes during free_initmem, so that init memory can be
reclaimed.
This uses section size instead of PMD size to reduce memory lost to
padding on non-LPAE systems.
Based on work by Brad Spengler, Larry Bassel, and Laura Abbott.
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <lauraa@codeaurora.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index ae69809..7a0756d 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -1008,3 +1008,12 @@
help
This option specifies the architecture can support big endian
operation.
+
+config ARM_KERNMEM_PERMS
+ bool "Restrict kernel memory permissions"
+ help
+ If this is set, kernel memory other than kernel text (and rodata)
+ will be made non-executable. The tradeoff is that each region is
+ padded to section-size (1MiB) boundaries (because their permissions
+ are different and splitting the 1M pages into 4K ones causes TLB
+ performance problems), wasting memory.