powerpc: Add skeleton for Kernel Userspace Execution Prevention

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.leroy@c-s.fr>
[mpe: Don't split strings, use pr_crit_ratelimited()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

5 files changed, 34 insertions, 6 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..a53df74589e5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2843,7 +2843,7 @@
                         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..a2a959cb4e36 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 /* CONFIG_PPC_KUEP */
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_KUP_H_ */
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 887f11bcf330..3384354abc1d 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -229,11 +229,10 @@ static bool bad_kernel_fault(bool is_exec, unsigned long error_code,
         /* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on others */
         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) -"
-                                   "exploit attempt? (uid: %d)\n",
-                                   address, from_kuid(&init_user_ns,
-                                                      current_uid()));
+                pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
+                                    address >= TASK_SIZE ? "exec-protected" : "user",
+                                    address,
+                                    from_kuid(&init_user_ns, current_uid()));
         }
         return is_exec || (address >= TASK_SIZE);
 }
diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index 36d28e872289..83f95a5565d6 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);
 }
 
 #define CTOR(shift) static void ctor_##shift(void *addr) \
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 842b2c7e156a..7d30bbbaa3c1 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -345,6 +345,18 @@ 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