x86/spectre: Report get_user mitigation for spectre_v1

BugLink: https://bugs.launchpad.net/bugs/1774181

(cherry picked from commit edfbae53)

Reflect the presence of get_user(), __get_user(), and 'syscall' protections
in sysfs. The expectation is that new and better tooling will allow the
kernel to grow more usages of array_index_nospec(), for now, only claim
mitigation for __user pointer de-references.
Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: torvalds@linux-foundation.org
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727420158.33451.11658324346540434635.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: David Woodhouse <dwmw@amazon.co.uk>
[jwang: cherry pick to 4.4]
Signed-off-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(backported from commit b9c288b6 linux-4.4.y)
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/kernel/cpu/bugs.c

@@ -702,8 +702,8 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 		break;
 
 	case X86_BUG_SPECTRE_V1:
-		if (osb_is_enabled)
-			return sprintf(buf, "Mitigation: OSB (observable speculation barrier, Intel v6)\n");
+		return sprintf(buf, "Mitigation: __user pointer sanitization%s%s\n",
+			       osb_is_enabled ? ", OSB (observable speculation barrier, Intel v6)" : "");
 
 		break;