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>
edison-fw · Apr 21, 2019 · 0fb1c25 · 0fb1c25
1 parent 69795ca
commit 0fb1c25
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Showing 5 changed files with 34 additions and 6 deletions.
diff --git 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
@@ -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
@@ -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
@@ -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
@@ -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