[Xen-changelog] [xen-unstable] x86-64: detect processors subject to AMD erratum #121 and refuse to boot

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <JBeulich@xxxxxxxx>
# Date 1339497222 -3600
# Node ID bc2f3a848f9a7c23b4a3736d0215732b1f039219
# Parent  76eaf5966c05a4a10fd29eee6968977fd9d4ce6d
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@xxxxxxxx>
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r 76eaf5966c05 -r bc2f3a848f9a docs/misc/xen-command-line.markdown
--- a/docs/misc/xen-command-line.markdown       Tue Jun 12 11:33:40 2012 +0100
+++ b/docs/misc/xen-command-line.markdown       Tue Jun 12 11:33:42 2012 +0100
@@ -126,6 +126,16 @@ Override Xen's logic for choosing the AP
 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 -r 76eaf5966c05 -r bc2f3a848f9a xen/arch/x86/cpu/amd.c
--- a/xen/arch/x86/cpu/amd.c    Tue Jun 12 11:33:40 2012 +0100
+++ b/xen/arch/x86/cpu/amd.c    Tue Jun 12 11:33:42 2012 +0100
@@ -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 cp
                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 -r 76eaf5966c05 -r bc2f3a848f9a xen/include/asm-x86/amd.h
--- a/xen/include/asm-x86/amd.h Tue Jun 12 11:33:40 2012 +0100
+++ b/xen/include/asm-x86/amd.h Tue Jun 12 11:33:42 2012 +0100
@@ -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))
 

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