powerpc: Add framework for Kernel Userspace Protection

This patch adds a skeleton for Kernel Userspace Protection
functionnalities like Kernel Userspace Access Protection and Kernel
Userspace Execution Prevention

The subsequent implementation of KUAP for radix makes use of a MMU
feature in order to patch out assembly when KUAP is disabled or
unsupported. This won't work unless there's an entry point for KUP
support before the feature magic happens, so for PPC64 setup_kup() is
called early in setup.

On PPC32, feature_fixup() is done too early to allow the same.

Suggested-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

4 files changed, 26 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
new file mode 100644
index 000000000000..7a88b8b9b54d
--- /dev/null
+++ b/arch/powerpc/include/asm/kup.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_KUP_H_
+#define _ASM_POWERPC_KUP_H_
+
+#ifndef __ASSEMBLY__
+
+void setup_kup(void);
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* _ASM_POWERPC_KUP_H_ */
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index ba404dd9ce1d..6179c4200339 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -68,6 +68,7 @@
 #include <asm/cputhreads.h>
 #include <asm/hw_irq.h>
 #include <asm/feature-fixups.h>
+#include <asm/kup.h>
 
 #include "setup.h"
 
@@ -331,6 +332,12 @@ void __init early_setup(unsigned long dt_ptr)
          */
         configure_exceptions();
 
+        /*
+         * Configure Kernel Userspace Protection. This needs to happen before
+         * feature fixups for platforms that implement this using features.
+         */
+        setup_kup();
+
         /* Apply all the dynamic patching */
         apply_feature_fixups();
         setup_feature_keys();
diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index 1e6910eb70ed..36d28e872289 100644
--- a/arch/powerpc/mm/init-common.c
+++ b/arch/powerpc/mm/init-common.c
@@ -24,6 +24,11 @@
 #include <linux/string.h>
 #include <asm/pgalloc.h>
 #include <asm/pgtable.h>
+#include <asm/kup.h>
+
+void __init setup_kup(void)
+{
+}
 
 #define CTOR(shift) static void ctor_##shift(void *addr) \
 {                                                       \
diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
index 41a3513cadc9..80cc97cd8878 100644
--- a/arch/powerpc/mm/init_32.c
+++ b/arch/powerpc/mm/init_32.c
@@ -45,6 +45,7 @@
 #include <asm/tlb.h>
 #include <asm/sections.h>
 #include <asm/hugetlb.h>
+#include <asm/kup.h>
 
 #include "mmu_decl.h"
 
@@ -178,6 +179,8 @@ void __init MMU_init(void)
         btext_unmap();
 #endif
 
+        setup_kup();
+
         /* Shortly after that, the entire linear mapping will be available */
         memblock_set_current_limit(lowmem_end_addr);
 }