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-rw-r--r--system/xen/xsa/xsa320-4.13-3.patch36
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diff --git a/system/xen/xsa/xsa320-4.13-3.patch b/system/xen/xsa/xsa320-4.13-3.patch
new file mode 100644
index 0000000000000..b52eeb338adad
--- /dev/null
+++ b/system/xen/xsa/xsa320-4.13-3.patch
@@ -0,0 +1,36 @@
+From: Andrew Cooper <andrew.cooper3@citrix.com>
+Subject: x86/spec-ctrl: Update docs with SRBDS workaround
+
+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.pandoc b/docs/misc/xen-command-line.pandoc
+index c780312531..81e12d053c 100644
+--- a/docs/misc/xen-command-line.pandoc
++++ b/docs/misc/xen-command-line.pandoc
+@@ -481,12 +481,18 @@ 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
+ > `= fam_0f_rev_[cdefg] | fam_10_rev_[bc] | fam_11_rev_b`