1 files changed, 57 insertions, 0 deletions
diff --git a/main/xen/xsa320-4.11-3.patch b/main/xen/xsa320-4.11-3.patch
new file mode 100644
index 00000000000..ff7990b2027
--- /dev/null
+++ b/main/xen/xsa320-4.11-3.patch
@@ -0,0 +1,57 @@
+From: Andrew Cooper <andrew.cooper3@citrix.com>
+Subject: x86/spec-ctrl: Allow the RDRAND/RDSEED features to be hidden
+
+RDRAND/RDSEED can be hidden using cpuid= to mitigate SRBDS if microcode
+isn't available.
+
+This is part of XSA-320 / CVE-2020-0543.
+
+Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
+Acked-by: Julien Grall <jgrall@amazon.com>
+
+diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
+index 3356e59fee..ac397e7de0 100644
+--- a/docs/misc/xen-command-line.markdown
++++ b/docs/misc/xen-command-line.markdown
+@@ -487,12 +487,18 @@ choice of `dom0-kernel` is deprecated and not supported by all Dom0 kernels.
+ This option allows for fine tuning of the facilities Xen will use, after
+ accounting for hardware capabilities as enumerated via CPUID.
+ 
++Unless otherwise noted, options only have any effect in their negative form,
++to hide the named feature(s).  Ignoring a feature using this mechanism will
++cause Xen not to use the feature, nor offer them as usable to guests.
++
+ Currently accepted:
+ 
+ The Speculation Control hardware features `srbds-ctrl`, `md-clear`, `ibrsb`,
+ `stibp`, `ibpb`, `l1d-flush` and `ssbd` are used by default if available and
+-applicable.  They can be ignored, e.g. `no-ibrsb`, at which point Xen won't
+-use them itself, and won't offer them to guests.
++applicable.  They can all be ignored.
++
++`rdrand` and `rdseed` can be ignored, as a mitigation to XSA-320 /
++CVE-2020-0543.
+ 
+ ### cpuid\_mask\_cpu (AMD only)
+ > `= fam_0f_rev_c | fam_0f_rev_d | fam_0f_rev_e | fam_0f_rev_f | fam_0f_rev_g | fam_10_rev_b | fam_10_rev_c | fam_11_rev_b`
+diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
+index b8e5b6fe67..78d08dbb32 100644
+--- a/xen/arch/x86/cpuid.c
++++ b/xen/arch/x86/cpuid.c
+@@ -63,6 +63,16 @@ static int __init parse_xen_cpuid(const char *s)
+             if ( !val )
+                 setup_clear_cpu_cap(X86_FEATURE_SRBDS_CTRL);
+         }
++        else if ( (val = parse_boolean("rdrand", s, ss)) >= 0 )
++        {
++            if ( !val )
++                setup_clear_cpu_cap(X86_FEATURE_RDRAND);
++        }
++        else if ( (val = parse_boolean("rdseed", s, ss)) >= 0 )
++        {
++            if ( !val )
++                setup_clear_cpu_cap(X86_FEATURE_RDSEED);
++        }
+         else
+             rc = -EINVAL;
+