From: Andrew Cooper Date: Wed, 10 Jun 2020 17:57:00 +0000 (+0100) Subject: x86/spec-ctrl: Update docs with SRBDS workaround X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~85 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=7028534d8482d25860c4d1aa8e45f0b911abfc5a;p=xen.git 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 Acked-by: Julien Grall --- diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc index 1a69c60139..fde749c669 100644 --- a/docs/misc/xen-command-line.pandoc +++ b/docs/misc/xen-command-line.pandoc @@ -502,16 +502,21 @@ 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` can be used to override the default disabling of the feature on certain -AMD systems. Its negative form can of course also be used to suppress use and -exposure of the feature. +`rdrand` and `rdseed` can be ignored, as a mitigation to XSA-320 / +CVE-2020-0543. The RDRAND feature is disabled by default on certain AMD +systems, due to possible malfunctions after ACPI S3 suspend/resume. `rdrand` +may be used in its positive form to override Xen's default behaviour on these +systems, and make the feature fully usable. ### cpuid_mask_cpu > `= fam_0f_rev_[cdefg] | fam_10_rev_[bc] | fam_11_rev_b`