[RFC PATCH v2 03/11] powerpc: Add skeleton for Kernel Userspace Execution Prevention

[Christophe Leroy]

This patch adds a skeleton for Kernel Userspace Execution Prevention.

Then subarches implementing it have to define CONFIG_PPC_HAVE_KUEP
and provide setup_kuep() function.

Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 +-
 arch/powerpc/include/asm/kup.h                  |  6 ++++++
 arch/powerpc/mm/fault.c                         |  3 ++-
 arch/powerpc/mm/init-common.c                   | 11 +++++++++++
 arch/powerpc/platforms/Kconfig.cputype          | 12 ++++++++++++
 5 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index 81d1d5a74728..1103549363bb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2796,7 +2796,7 @@
                        Disable SMAP (Supervisor Mode Access Prevention)
                        even if it is supported by processor.
 
-       nosmep          [X86]
+       nosmep          [X86,PPC]
                        Disable SMEP (Supervisor Mode Execution Prevention)
                        even if it is supported by processor.
 
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 7a88b8b9b54d..af4b5f854ca4 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -6,6 +6,12 @@
 
 void setup_kup(void);
 
+#ifdef CONFIG_PPC_KUEP
+void setup_kuep(bool disabled);
+#else
+static inline void setup_kuep(bool disabled) { }
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_KUP_H_ */
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 50e5c790d11e..e57bd46cf25b 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -230,8 +230,9 @@ static bool bad_kernel_fault(bool is_exec, unsigned long 
error_code,
        if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT |
                                      DSISR_PROTFAULT))) {
                printk_ratelimited(KERN_CRIT "kernel tried to execute"
-                                  " exec-protected page (%lx) -"
+                                  " %s page (%lx) -"
                                   "exploit attempt? (uid: %d)\n",
+                                  address >= TASK_SIZE ? "exec-protected" : 
"user",
                                   address, from_kuid(&init_user_ns,
                                                      current_uid()));
        }
diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index a72bbfc3add6..37f84a43b822 100644
--- a/arch/powerpc/mm/init-common.c
+++ b/arch/powerpc/mm/init-common.c
@@ -26,8 +26,19 @@
 #include <asm/pgtable.h>
 #include <asm/kup.h>
 
+static bool disable_kuep = !IS_ENABLED(CONFIG_PPC_KUEP);
+
+static int __init parse_nosmep(char *p)
+{
+       disable_kuep = true;
+       pr_warn("Disabling Kernel Userspace Execution Prevention\n");
+       return 0;
+}
+early_param("nosmep", parse_nosmep);
+
 void __init setup_kup(void)
 {
+       setup_kuep(disable_kuep);
 }
 
 static void pgd_ctor(void *addr)
diff --git a/arch/powerpc/platforms/Kconfig.cputype 
b/arch/powerpc/platforms/Kconfig.cputype
index f4e2c5729374..70830cb3c18a 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -351,6 +351,18 @@ config PPC_RADIX_MMU_DEFAULT
 
          If you're unsure, say Y.
 
+config PPC_HAVE_KUEP
+       bool
+
+config PPC_KUEP
+       bool "Kernel Userspace Execution Prevention"
+       depends on PPC_HAVE_KUEP
+       default y
+       help
+         Enable support for Kernel Userspace Execution Prevention (KUEP)
+
+         If you're unsure, say Y.
+
 config ARCH_ENABLE_HUGEPAGE_MIGRATION
        def_bool y
        depends on PPC_BOOK3S_64 && HUGETLB_PAGE && MIGRATION
-- 
2.13.3