linux-kernel - [PATCH 3/7] powerpc/8xx: Add Kernel Userspace Execution Prevention

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Date:   Tue,  5 Mar 2019 21:18:16 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, ruscur@...sell.cc
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 3/7] powerpc/8xx: Add Kernel Userspace Execution Prevention

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@....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 5e53b9fd62aa..08966e3127bb 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