[IA64] sysctl option to silence unaligned trap warnings

Allow sysadmin to disable all warnings about userland apps
making unaligned accesses by using:
 # echo 1 > /proc/sys/kernel/ignore-unaligned-usertrap
Rather than having to use prctl on a process by process basis.

Default behaivour leaves the warnings enabled.
Signed-off-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/unaligned.c

@@ -52,6 +52,15 @@ dump (const char *str, void *vp, size_t len)
 #define IA64_FIRST_ROTATING_FR	32
 #define SIGN_EXT9		0xffffffffffffff00ul
 
+/*
+ *  sysctl settable hook which tells the kernel whether to honor the
+ *  IA64_THREAD_UAC_NOPRINT prctl.  Because this is user settable, we want
+ *  to allow the super user to enable/disable this for security reasons
+ *  (i.e. don't allow attacker to fill up logs with unaligned accesses).
+ */
+int no_unaligned_warning;
+static int noprint_warning;
+
 /*
  * For M-unit:
  *
@@ -1324,8 +1333,9 @@ ia64_handle_unaligned (unsigned long ifa, struct pt_regs *regs)
 		if ((current->thread.flags & IA64_THREAD_UAC_SIGBUS) != 0)
 			goto force_sigbus;
 
-		if (!(current->thread.flags & IA64_THREAD_UAC_NOPRINT)
-		    && within_logging_rate_limit())
+		if (!no_unaligned_warning &&
+		    !(current->thread.flags & IA64_THREAD_UAC_NOPRINT) &&
+		    within_logging_rate_limit())
 		{
 			char buf[200];	/* comm[] is at most 16 bytes... */
 			size_t len;
@@ -1340,7 +1350,22 @@ ia64_handle_unaligned (unsigned long ifa, struct pt_regs *regs)
 			if (user_mode(regs))
 				tty_write_message(current->signal->tty, buf);
 			buf[len-1] = '\0';	/* drop '\r' */
-			printk(KERN_WARNING "%s", buf);	/* watch for command names containing %s */
+			/* watch for command names containing %s */
+			printk(KERN_WARNING "%s", buf);
+		} else {
+			if (no_unaligned_warning && !noprint_warning) {
+				noprint_warning = 1;
+				printk(KERN_WARNING "%s(%d) encountered an "
+				       "unaligned exception which required\n"
+				       "kernel assistance, which degrades "
+				       "the performance of the application.\n"
+				       "Unaligned exception warnings have "
+				       "been disabled by the system "
+				       "administrator\n"
+				       "echo 0 > /proc/sys/kernel/ignore-"
+				       "unaligned-usertrap to re-enable\n",
+				       current->comm, current->pid);
+			}
 		}
 	} else {
 		if (within_logging_rate_limit())

include/linux/sysctl.h

@@ -147,6 +147,7 @@ enum
 	KERN_SETUID_DUMPABLE=69, /* int: behaviour of dumps for setuid core */
 	KERN_SPIN_RETRY=70,	/* int: number of spinlock retries */
 	KERN_ACPI_VIDEO_FLAGS=71, /* int: flags for setting up video after ACPI sleep */
+	KERN_IA64_UNALIGNED=72, /* int: ia64 unaligned userland trap enable */
 };
 
 

kernel/sysctl.c

@@ -124,6 +124,10 @@ extern int sysctl_hz_timer;
 extern int acct_parm[];
 #endif
 
+#ifdef CONFIG_IA64
+extern int no_unaligned_warning;
+#endif
+
 static int parse_table(int __user *, int, void __user *, size_t __user *, void __user *, size_t,
 		       ctl_table *, void **);
 static int proc_doutsstring(ctl_table *table, int write, struct file *filp,
@@ -665,6 +669,16 @@ static ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+#endif
+#ifdef CONFIG_IA64
+	{
+		.ctl_name	= KERN_IA64_UNALIGNED,
+		.procname	= "ignore-unaligned-usertrap",
+		.data		= &no_unaligned_warning,
+		.maxlen		= sizeof (int),
+	 	.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 #endif
 	{ .ctl_name = 0 }
 };