From: Jan Beulich <JBeulich@suse.com>
Date: Tue, 12 Jun 2012 10:33:42 +0000 (+0100)
Subject: x86-64: detect processors subject to AMD erratum #121 and refuse to boot
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~8321
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=3a07eef100625b43bf2b63c34a1c32d823f7764b;p=xen.git

x86-64: detect processors subject to AMD erratum #121 and refuse to boot

Processors with this erratum are subject to a DoS attack by unprivileged
guest users.

This is XSA-9 / CVE-2012-2934.

Signed-off-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>
---

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index 1f3faaa6de..7ceaa3b555 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -126,6 +126,16 @@ Override Xen's logic for choosing the APIC driver.  By default, if
 there are more than 8 CPUs, Xen will switch to `bigsmp` over
 `default`.
 
+### allow\_unsafe
+> `= <boolean>`
+
+Force boot on potentially unsafe systems. By default Xen will refuse to boot on
+systems with the following errata:
+
+* AMD Erratum 121. Processors with this erratum are subject to a guest
+  triggerable Denial of Service. Override only if you trust all of your PV
+  guests.
+
 ### apic\_verbosity
 > `= verbose | debug`
 
diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index b8c3a32480..81f7196827 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -32,6 +32,9 @@
 static char opt_famrev[14];
 string_param("cpuid_mask_cpu", opt_famrev);
 
+static bool_t opt_allow_unsafe;
+boolean_param("allow_unsafe", opt_allow_unsafe);
+
 static inline void wrmsr_amd(unsigned int index, unsigned int lo, 
 		unsigned int hi)
 {
@@ -493,6 +496,11 @@ static void __devinit init_amd(struct cpuinfo_x86 *c)
 		clear_bit(X86_FEATURE_MWAIT, c->x86_capability);
 
 #ifdef __x86_64__
+	if (cpu_has_amd_erratum(c, AMD_ERRATUM_121) && !opt_allow_unsafe)
+		panic("Xen will not boot on this CPU for security reasons.\n"
+		      "Pass \"allow_unsafe\" if you're trusting all your"
+		      " (PV) guest kernels.\n");
+
 	/* AMD CPUs do not support SYSENTER outside of legacy mode. */
 	clear_bit(X86_FEATURE_SEP, c->x86_capability);
 
diff --git a/xen/include/asm-x86/amd.h b/xen/include/asm-x86/amd.h
index 9a7fa3be65..94bd9cce09 100644
--- a/xen/include/asm-x86/amd.h
+++ b/xen/include/asm-x86/amd.h
@@ -127,6 +127,9 @@
 #define AMD_MODEL_RANGE_START(range)    (((range) >> 12) & 0xfff)
 #define AMD_MODEL_RANGE_END(range)      ((range) & 0xfff)
 
+#define AMD_ERRATUM_121                                                 \
+    AMD_LEGACY_ERRATUM(AMD_MODEL_RANGE(0x0f, 0x0, 0x0, 0x3f, 0xf))
+
 #define AMD_ERRATUM_170                                                 \
     AMD_LEGACY_ERRATUM(AMD_MODEL_RANGE(0x0f, 0x0, 0x0, 0x67, 0xf))