linux-kernel - [PATCH v3 02/22] powerpc/8xx: Activate KUEP at all time

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Date:   Tue, 19 Oct 2021 09:29:13 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v3 02/22] powerpc/8xx: Activate KUEP at all time

On the 8xx, there is absolutely no runtime impact with KUEP. Protection
against execution of user code in kernel mode is set up at boot time
by configuring the groups with contain all user pages as having swapped
protection rights, in extenso EX for user and NA for supervisor.

Configure KUEP at startup and force selection of CONFIG_PPC_KUEP.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/include/asm/nohash/32/mmu-8xx.h | 6 ++----
 arch/powerpc/mm/nohash/8xx.c                 | 5 -----
 arch/powerpc/platforms/Kconfig.cputype       | 1 +
 3 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
index 997cec973406..0e93a4728c9e 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
@@ -39,12 +39,10 @@
  * 0 => Kernel => 11 (all accesses performed according as user iaw page definition)
  * 1 => Kernel+Accessed => 01 (all accesses performed according to page definition)
  * 2 => User => 11 (all accesses performed according as user iaw page definition)
- * 3 => User+Accessed => 00 (all accesses performed as supervisor iaw page definition) for INIT
- *                    => 10 (all accesses performed according to swaped page definition) for KUEP
+ * 3 => User+Accessed => 10 (all accesses performed according to swaped page definition) for KUEP
  * 4-15 => Not Used
  */
-#define MI_APG_INIT	0xdc000000
-#define MI_APG_KUEP	0xde000000
+#define MI_APG_INIT	0xde000000
 
 /* The effective page number register.  When read, contains the information
  * about the last instruction TLB miss.  When MI_RPN is written, bits in
diff --git a/arch/powerpc/mm/nohash/8xx.c b/arch/powerpc/mm/nohash/8xx.c
index baa1f8a40af8..e878e8124ee6 100644
--- a/arch/powerpc/mm/nohash/8xx.c
+++ b/arch/powerpc/mm/nohash/8xx.c
@@ -215,12 +215,7 @@ void __init setup_initial_memory_limit(phys_addr_t first_memblock_base,
 #ifdef CONFIG_PPC_KUEP
 void 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 a208997ade88..66650ec1c7e6 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -43,6 +43,7 @@ config PPC_8xx
 	select ARCH_SUPPORTS_HUGETLBFS
 	select FSL_SOC
 	select PPC_HAVE_KUEP
+	select PPC_KUEP
 	select PPC_HAVE_KUAP
 	select HAVE_ARCH_VMAP_STACK
 	select HUGETLBFS
-- 
2.31.1