1 files changed, 58 insertions, 4 deletions

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 1f1f2d54dab5..dabbac30acdf 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -82,6 +82,57 @@
 #define UMIP_INST_SLDT  3       /* 0F 00 /0 */
 #define UMIP_INST_STR   4       /* 0F 00 /1 */
 
+const char * const umip_insns[5] = {
+        [UMIP_INST_SGDT] = "SGDT",
+        [UMIP_INST_SIDT] = "SIDT",
+        [UMIP_INST_SMSW] = "SMSW",
+        [UMIP_INST_SLDT] = "SLDT",
+        [UMIP_INST_STR] = "STR",
+};
+
+#define umip_pr_err(regs, fmt, ...) \
+        umip_printk(regs, KERN_ERR, fmt, ##__VA_ARGS__)
+#define umip_pr_warning(regs, fmt, ...) \
+        umip_printk(regs, KERN_WARNING, fmt,  ##__VA_ARGS__)
+
+/**
+ * umip_printk() - Print a rate-limited message
+ * @regs:       Register set with the context in which the warning is printed
+ * @log_level:  Kernel log level to print the message
+ * @fmt:        The text string to print
+ *
+ * Print the text contained in @fmt. The print rate is limited to bursts of 5
+ * messages every two minutes. The purpose of this customized version of
+ * printk() is to print messages when user space processes use any of the
+ * UMIP-protected instructions. Thus, the printed text is prepended with the
+ * task name and process ID number of the current task as well as the
+ * instruction and stack pointers in @regs as seen when entering kernel mode.
+ *
+ * Returns:
+ *
+ * None.
+ */
+static __printf(3, 4)
+void umip_printk(const struct pt_regs *regs, const char *log_level,
+                 const char *fmt, ...)
+{
+        /* Bursts of 5 messages every two minutes */
+        static DEFINE_RATELIMIT_STATE(ratelimit, 2 * 60 * HZ, 5);
+        struct task_struct *tsk = current;
+        struct va_format vaf;
+        va_list args;
+
+        if (!__ratelimit(&ratelimit))
+                return;
+
+        va_start(args, fmt);
+        vaf.fmt = fmt;
+        vaf.va = &args;
+        printk("%s" pr_fmt("%s[%d] ip:%lx sp:%lx: %pV"), log_level, tsk->comm,
+               task_pid_nr(tsk), regs->ip, regs->sp, &vaf);
+        va_end(args);
+}
+
 /**
  * identify_insn() - Identify a UMIP-protected instruction
  * @insn:       Instruction structure with opcode and ModRM byte.
@@ -236,10 +287,8 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
         if (!(show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)))
                 return;
 
-        pr_err_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%x in %lx\n",
-                           tsk->comm, task_pid_nr(tsk), regs->ip,
-                           regs->sp, X86_PF_USER | X86_PF_WRITE,
-                           regs->ip);
+        umip_pr_err(regs, "segfault in emulation. error%x\n",
+                    X86_PF_USER | X86_PF_WRITE);
 }
 
 /**
@@ -326,10 +375,15 @@ bool fixup_umip_exception(struct pt_regs *regs)
         if (umip_inst < 0)
                 return false;
 
+        umip_pr_warning(regs, "%s instruction cannot be used by applications.\n",
+                        umip_insns[umip_inst]);
+
         /* Do not emulate SLDT, STR or user long mode processes. */
         if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
                 return false;
 
+        umip_pr_warning(regs, "For now, expensive software emulation returns the result.\n");
+
         if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
                 return false;