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Subject[PATCH v2 06/10] powerpc/8xx: Add Kernel Userspace Execution Prevention
Date
This patch adds Kernel Userspace Execution Prevention on the 8xx.

When a page is Executable, it is set Executable for Key 0 and NX
for Key 1.

Up to now, the User group is defined with Key 0 for both User and
Supervisor.

By changing the group to Key 0 for User and Key 1 for Supervisor,
this patch prevents the Kernel from being able to execute user code.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/include/asm/nohash/32/mmu-8xx.h | 7 +++++++
arch/powerpc/mm/8xx_mmu.c | 12 ++++++++++++
arch/powerpc/platforms/Kconfig.cputype | 1 +
3 files changed, 20 insertions(+)

diff --git a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
index fc5a653d5dd2..3cb743284e09 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
@@ -41,6 +41,13 @@
*/
#define MI_APG_INIT 0x4fffffff

+/*
+ * 0 => Kernel => 01 (all accesses performed according to page definition)
+ * 1 => User => 10 (all accesses performed according to swaped page definition)
+ * 2-16 => NA => 11 (all accesses performed as user iaw page definition)
+ */
+#define MI_APG_KUEP 0x6fffffff
+
/* The effective page number register. When read, contains the information
* about the last instruction TLB miss. When MI_RPN is written, bits in
* this register are used to create the TLB entry.
diff --git a/arch/powerpc/mm/8xx_mmu.c b/arch/powerpc/mm/8xx_mmu.c
index fe1f6443d57f..e257a0c9bd08 100644
--- a/arch/powerpc/mm/8xx_mmu.c
+++ b/arch/powerpc/mm/8xx_mmu.c
@@ -213,3 +213,15 @@ void flush_instruction_cache(void)
mtspr(SPRN_IC_CST, IDC_INVALL);
isync();
}
+
+#ifdef CONFIG_PPC_KUEP
+void __init setup_kuep(bool disabled)
+{
+ if (disabled)
+ return;
+
+ pr_info("Activating Kernel Userspace Execution Prevention\n");
+
+ mtspr(SPRN_MI_AP, MI_APG_KUEP);
+}
+#endif
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 2e45a6e2bc99..00fa0d110dcb 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -34,6 +34,7 @@ config PPC_8xx
bool "Freescale 8xx"
select FSL_SOC
select SYS_SUPPORTS_HUGETLBFS
+ select PPC_HAVE_KUEP

config 40x
bool "AMCC 40x"
--
2.13.3
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