x86: uaccess: introduce try and catch framework

Impact: introduce new uaccess exception handling framework

Introduce {get|put}_user_try and {get|put}_user_catch as new uaccess exception
handling framework.
{get|put}_user_try begins exception block and {get|put}_user_catch(err) ends
the block and gets err if an exception occured in {get|put}_user_ex() in the
block. The exception is stored thread_info->uaccess_err.

The example usage of this framework is below;
int func()
{
	int err = 0;

	get_user_try {
		get_user_ex(...);
		get_user_ex(...);
		:
	} get_user_catch(err);

	return err;
}

Note: get_user_ex() is not clear the value when an exception occurs, it's
different from the behavior of __get_user(), but I think it doesn't matter.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 7e8db53528a7..61b41ca3b5a2 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -23,6 +23,12 @@ int fixup_exception(struct pt_regs *regs)
 
 	fixup = search_exception_tables(regs->ip);
 	if (fixup) {
+		/* If fixup is less than 16, it means uaccess error */
+		if (fixup->fixup < 16) {
+			current_thread_info()->uaccess_err = -EFAULT;
+			regs->ip += fixup->fixup;
+			return 1;
+		}
 		regs->ip = fixup->fixup;
 		return 1;
 	}