parisc: add strict copy size checks (v2)

Add CONFIG_DEBUG_STRICT_USER_COPY_CHECKS, copied from the x86
implementation. Tested with 32 and 64bit kernel.

Signed-off-by: Helge Deller <[e-mail]>
Signed-off-by: Kyle McMartin <[e-mail]>

arch/parisc/Kconfig.debug

···
          portion of the kernel code won't be covered by a TLB anymore.
          If in doubt, say "N".
 
+config DEBUG_STRICT_USER_COPY_CHECKS
+	bool "Strict copy size checks"
+	depends on DEBUG_KERNEL && !TRACE_BRANCH_PROFILING
+	---help---
+	  Enabling this option turns a certain set of sanity checks for user
+	  copy operations into compile time failures.
+
+	  The copy_from_user() etc checks are there to help test if there
+	  are sufficient security checks on the length argument of
+	  the copy operation, by having gcc prove that the argument is
+	  within bounds.
+
+	  If unsure, or if you run an older (pre 4.4) gcc, say N.
+
 endmenu

arch/parisc/include/asm/uaccess.h

···
 #include <asm/page.h>
 #include <asm/system.h>
 #include <asm/cache.h>
+#include <asm/errno.h>
 #include <asm-generic/uaccess-unaligned.h>
 
 #define VERIFY_READ 0
···
 
 unsigned long copy_to_user(void __user *dst, const void *src, unsigned long len);
 #define __copy_to_user copy_to_user
-unsigned long copy_from_user(void *dst, const void __user *src, unsigned long len);
-#define __copy_from_user copy_from_user
+unsigned long __copy_from_user(void *dst, const void __user *src, unsigned long len);
 unsigned long copy_in_user(void __user *dst, const void __user *src, unsigned long len);
 #define __copy_in_user copy_in_user
 #define __copy_to_user_inatomic __copy_to_user
 #define __copy_from_user_inatomic __copy_from_user
+
+extern void copy_from_user_overflow(void)
+#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS
+        __compiletime_error("copy_from_user() buffer size is not provably correct")
+#else
+        __compiletime_warning("copy_from_user() buffer size is not provably correct")
+#endif
+;
+
+static inline unsigned long __must_check copy_from_user(void *to,
+                                          const void __user *from,
+                                          unsigned long n)
+{
+        int sz = __compiletime_object_size(to);
+        int ret = -EFAULT;
+
+        if (likely(sz == -1 || !__builtin_constant_p(n) || sz >= n))
+                ret = __copy_from_user(to, from, n);
+        else
+                copy_from_user_overflow();
+
+        return ret;
+}
 
 struct pt_regs;
 int fixup_exception(struct pt_regs *regs);

arch/parisc/lib/memcpy.c

···
 	return pa_memcpy((void __force *)dst, src, len);
 }
 
-unsigned long copy_from_user(void *dst, const void __user *src, unsigned long len)
+EXPORT_SYMBOL(__copy_from_user);
+unsigned long __copy_from_user(void *dst, const void __user *src, unsigned long len)
 {
 	mtsp(get_user_space(), 1);
 	mtsp(get_kernel_space(), 2);