3 files changed, 51 insertions, 9 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 94caefb550bf..d40d0ef389db 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -753,6 +753,7 @@ ENDPROC(__switch_to)
         .endr
         .endm
 
+#ifdef CONFIG_KUSER_HELPERS
         .align  5
         .globl  __kuser_helper_start
 __kuser_helper_start:
@@ -939,6 +940,8 @@ __kuser_helper_version:				@ 0xffff0ffc
         .globl  __kuser_helper_end
 __kuser_helper_end:
 
+#endif
+
  THUMB( .thumb  )
 
 /*
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 2c8c7fa78b8c..e3ca35ccd38e 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -800,15 +800,26 @@ void __init trap_init(void)
         return;
 }
 
-static void __init kuser_get_tls_init(unsigned long vectors)
+#ifdef CONFIG_KUSER_HELPERS
+static void __init kuser_init(void *vectors)
 {
+        extern char __kuser_helper_start[], __kuser_helper_end[];
+        int kuser_sz = __kuser_helper_end - __kuser_helper_start;
+
+        memcpy(vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
+
         /*
          * vectors + 0xfe0 = __kuser_get_tls
          * vectors + 0xfe8 = hardware TLS instruction at 0xffff0fe8
          */
         if (tls_emu || has_tls_reg)
-                memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfe8, 4);
+                memcpy(vectors + 0xfe0, vectors + 0xfe8, 4);
+}
+#else
+static void __init kuser_init(void *vectors)
+{
 }
+#endif
 
 void __init early_trap_init(void *vectors_base)
 {
@@ -816,8 +827,6 @@ void __init early_trap_init(void *vectors_base)
         unsigned long vectors = (unsigned long)vectors_base;
         extern char __stubs_start[], __stubs_end[];
         extern char __vectors_start[], __vectors_end[];
-        extern char __kuser_helper_start[], __kuser_helper_end[];
-        int kuser_sz = __kuser_helper_end - __kuser_helper_start;
         unsigned i;
 
         vectors_page = vectors_base;
@@ -838,12 +847,8 @@ void __init early_trap_init(void *vectors_base)
          */
         memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);
         memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);
-        memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
 
-        /*
-         * Do processor specific fixups for the kuser helpers
-         */
-        kuser_get_tls_init(vectors);
+        kuser_init(vectors_base);
 
         /*
          * Copy signal return handlers into the vector page, and
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 6cacdc8dd654..db5c2cab8fda 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -421,24 +421,28 @@ config CPU_32v3
         select CPU_USE_DOMAINS if MMU
         select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
         select TLS_REG_EMUL if SMP || !MMU
+        select NEED_KUSER_HELPERS
 
 config CPU_32v4
         bool
         select CPU_USE_DOMAINS if MMU
         select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
         select TLS_REG_EMUL if SMP || !MMU
+        select NEED_KUSER_HELPERS
 
 config CPU_32v4T
         bool
         select CPU_USE_DOMAINS if MMU
         select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
         select TLS_REG_EMUL if SMP || !MMU
+        select NEED_KUSER_HELPERS
 
 config CPU_32v5
         bool
         select CPU_USE_DOMAINS if MMU
         select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
         select TLS_REG_EMUL if SMP || !MMU
+        select NEED_KUSER_HELPERS
 
 config CPU_32v6
         bool
@@ -776,6 +780,7 @@ config CPU_BPREDICT_DISABLE
 
 config TLS_REG_EMUL
         bool
+        select NEED_KUSER_HELPERS
         help
           An SMP system using a pre-ARMv6 processor (there are apparently
           a few prototypes like that in existence) and therefore access to
@@ -783,11 +788,40 @@ config TLS_REG_EMUL
 
 config NEEDS_SYSCALL_FOR_CMPXCHG
         bool
+        select NEED_KUSER_HELPERS
         help
           SMP on a pre-ARMv6 processor?  Well OK then.
           Forget about fast user space cmpxchg support.
           It is just not possible.
 
+config NEED_KUSER_HELPERS
+        bool
+
+config KUSER_HELPERS
+        bool "Enable kuser helpers in vector page" if !NEED_KUSER_HELPERS
+        default y
+        help
+          Warning: disabling this option may break user programs.
+
+          Provide kuser helpers in the vector page.  The kernel provides
+          helper code to userspace in read only form at a fixed location
+          in the high vector page to allow userspace to be independent of
+          the CPU type fitted to the system.  This permits binaries to be
+          run on ARMv4 through to ARMv7 without modification.
+
+          However, the fixed address nature of these helpers can be used
+          by ROP (return orientated programming) authors when creating
+          exploits.
+
+          If all of the binaries and libraries which run on your platform
+          are built specifically for your platform, and make no use of
+          these helpers, then you can turn this option off.  However,
+          when such an binary or library is run, it will receive a SIGILL
+          signal, which will terminate the program.
+
+          Say N here only if you are absolutely certain that you do not
+          need these helpers; otherwise, the safe option is to say Y.
+
 config DMA_CACHE_RWFO
         bool "Enable read/write for ownership DMA cache maintenance"
         depends on CPU_V6K && SMP