[PATCH v10 10/18] x86/insn-eval: Do not BUG on invalid register type

[Ricardo Neri]

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.

Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 arch/x86/lib/insn-eval.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index df9418c..4931d92 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/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) {
-- 
2.7.4