[RFC PATCH 1/5] arm: mm: add CONFIG_STRICT_MEMORY_RWX

[Laura Abbott]

From: Larry Bassel <lbassel at codeaurora.org>

If this is set, kernel text will be made RX, kernel data and stack
RW, rodata R so that writing to kernel text, executing kernel data
or stack, or writing to read-only data or kernel text will not
succeed.

Signed-off-by: Larry Bassel <lbassel at codeaurora.org>
Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
---
 arch/arm/mm/Kconfig |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index cd2c88e..c223d5c 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -952,3 +952,15 @@ config ARCH_HAS_BARRIERS
 	help
 	  This option allows the use of custom mandatory barriers
 	  included via the mach/barriers.h file.
+
+config STRICT_MEMORY_RWX
+	bool "restrict kernel memory permissions as much as possible"
+	default n
+	help
+	  If this is set, kernel text will be made RX, kernel data and stack
+	  RW, rodata R (otherwise all of the kernel 1-to-1 mapping is
+	  made RWX).
+	  The tradeoff is that several sections are padded to
+	  1M boundaries (because their permissions are different and
+	  splitting the 1M pages into 4K ones causes TLB performance
+	  problems), wasting memory.
-- 
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