x86/insn-eval: Do not BUG on invalid register type

We are not in a critical failure path. The invalid register type is caused
when trying to decode invalid instruction bytes from a user-space program.
Thus, simply print an error message. To prevent this warning from being
abused from user space programs, use the rate-limited variant of pr_err().
along with a descriptive prefix.

Signed-off-by: Ricardo Neri <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Borislav Petkov <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: [email protected]
Cc: Adrian Hunter <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: "Ravi V. Shankar" <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Chen Yucong <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Thomas Garnier <[email protected]>
Link: https://lkml.kernel.org/r/1509135945-13762-11-git-send-email-ricardo.neri-calderon@linux.intel.com

arch/x86/lib/insn-eval.c

@@ -5,10 +5,14 @@
  */
 #include <linux/kernel.h>
 #include <linux/string.h>
+#include <linux/ratelimit.h>
 #include <asm/inat.h>
 #include <asm/insn.h>
 #include <asm/insn-eval.h>
 
+#undef pr_fmt
+#define pr_fmt(fmt) "insn: " fmt
+
 enum reg_type {
 	REG_TYPE_RM = 0,
 	REG_TYPE_INDEX,
@@ -85,9 +89,8 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 		break;
 
 	default:
-		pr_err("invalid register type");
-		BUG();
-		break;
+		pr_err_ratelimited("invalid register type: %d\n", type);
+		return -EINVAL;
 	}
 
 	if (regno >= nr_registers) {