[tip:x86/pti] x86/pti: Don't report XenPV as vulnerable

[tip-bot for Jiri Kosina]

Commit-ID:  66aa6b5cbc359331fc054e96bb49e9502bc0b1d9
Gitweb:     https://git.kernel.org/tip/66aa6b5cbc359331fc054e96bb49e9502bc0b1d9
Author:     Jiri Kosina <jkosina@xxxxxxx>
AuthorDate: Mon, 18 Jun 2018 09:59:54 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 19 Jun 2018 09:58:22 +0200

x86/pti: Don't report XenPV as vulnerable

Xen PV domain kernel is not by design affected by meltdown as it's
enforcing split CR3 itself. Let's not report such systems as "Vulnerable"
in sysfs (we're also already forcing PTI to off in X86_HYPER_XEN_PV cases);
the security of the system ultimately depends on presence of mitigation in
the Hypervisor, which can't be easily detected from DomU; let's report
that.

Reported-and-tested-by: Mike Latimer <mlatimer@xxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Juergen Gross <jgross@xxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1806180959080.6203@xxxxxxxxxxxxx

---
 arch/x86/kernel/cpu/bugs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index cd0fda1fff6d..57638396a254 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -27,6 +27,7 @@
 #include <asm/pgtable.h>
 #include <asm/set_memory.h>
 #include <asm/intel-family.h>
+#include <asm/hypervisor.h>
 
 static void __init spectre_v2_select_mitigation(void);
 static void __init ssb_select_mitigation(void);
@@ -664,6 +665,10 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 		if (boot_cpu_has(X86_FEATURE_PTI))
 			return sprintf(buf, "Mitigation: PTI\n");
 
+		if (hypervisor_is_type(X86_HYPER_XEN_PV))
+			return sprintf(buf, "Unknown (XEN PV detected, hypervisor "
+					    "mitigation required)\n");
+
 		break;
 
 	case X86_BUG_SPECTRE_V1: