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From 08bfd4d01185e94fda1be9dd79a981d890a9085e Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Tue, 12 Jul 2022 11:26:14 +0200
Subject: [PATCH 10/21] x86/spec-ctrl: Add fine-grained cmdline suboptions for
primitives
Support controling the PV/HVM suboption of msr-sc/rsb/md-clear, which
previously wasn't possible.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 27357c394ba6e1571a89105b840ce1c6f026485c
master date: 2022-07-11 15:21:35 +0100
---
docs/misc/xen-command-line.pandoc | 12 ++++--
xen/arch/x86/spec_ctrl.c | 66 ++++++++++++++++++++++++++-----
2 files changed, 66 insertions(+), 12 deletions(-)
diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 1db3da9ef78e..b06db5f654e5 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2169,7 +2169,8 @@ not be able to control the state of the mitigation.
By default SSBD will be mitigated at runtime (i.e `ssbd=runtime`).
### spec-ctrl (x86)
-> `= List of [ <bool>, xen=<bool>, {pv,hvm,msr-sc,rsb,md-clear}=<bool>,
+> `= List of [ <bool>, xen=<bool>, {pv,hvm}=<bool>,
+> {msr-sc,rsb,md-clear}=<bool>|{pv,hvm}=<bool>,
> bti-thunk=retpoline|lfence|jmp, {ibrs,ibpb,ssbd,psfd,
> eager-fpu,l1d-flush,branch-harden,srb-lock,
> unpriv-mmio}=<bool> ]`
@@ -2194,12 +2195,17 @@ in place for guests to use.
Use of a positive boolean value for either of these options is invalid.
-The booleans `pv=`, `hvm=`, `msr-sc=`, `rsb=` and `md-clear=` offer fine
+The `pv=`, `hvm=`, `msr-sc=`, `rsb=` and `md-clear=` options offer fine
grained control over the primitives by Xen. These impact Xen's ability to
-protect itself, and Xen's ability to virtualise support for guests to use.
+protect itself, and/or Xen's ability to virtualise support for guests to use.
* `pv=` and `hvm=` offer control over all suboptions for PV and HVM guests
respectively.
+* Each other option can be used either as a plain boolean
+ (e.g. `spec-ctrl=rsb` to control both the PV and HVM sub-options), or with
+ `pv=` or `hvm=` subsuboptions (e.g. `spec-ctrl=rsb=no-hvm` to disable HVM
+ RSB only).
+
* `msr-sc=` offers control over Xen's support for manipulating `MSR_SPEC_CTRL`
on entry and exit. These blocks are necessary to virtualise support for
guests and if disabled, guests will be unable to use IBRS/STIBP/SSBD/etc.
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 06790897e496..225fe08259b3 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -147,20 +147,68 @@ static int __init parse_spec_ctrl(const char *s)
opt_rsb_hvm = val;
opt_md_clear_hvm = val;
}
- else if ( (val = parse_boolean("msr-sc", s, ss)) >= 0 )
+ else if ( (val = parse_boolean("msr-sc", s, ss)) != -1 )
{
- opt_msr_sc_pv = val;
- opt_msr_sc_hvm = val;
+ switch ( val )
+ {
+ case 0:
+ case 1:
+ opt_msr_sc_pv = opt_msr_sc_hvm = val;
+ break;
+
+ case -2:
+ s += strlen("msr-sc=");
+ if ( (val = parse_boolean("pv", s, ss)) >= 0 )
+ opt_msr_sc_pv = val;
+ else if ( (val = parse_boolean("hvm", s, ss)) >= 0 )
+ opt_msr_sc_hvm = val;
+ else
+ default:
+ rc = -EINVAL;
+ break;
+ }
}
- else if ( (val = parse_boolean("rsb", s, ss)) >= 0 )
+ else if ( (val = parse_boolean("rsb", s, ss)) != -1 )
{
- opt_rsb_pv = val;
- opt_rsb_hvm = val;
+ switch ( val )
+ {
+ case 0:
+ case 1:
+ opt_rsb_pv = opt_rsb_hvm = val;
+ break;
+
+ case -2:
+ s += strlen("rsb=");
+ if ( (val = parse_boolean("pv", s, ss)) >= 0 )
+ opt_rsb_pv = val;
+ else if ( (val = parse_boolean("hvm", s, ss)) >= 0 )
+ opt_rsb_hvm = val;
+ else
+ default:
+ rc = -EINVAL;
+ break;
+ }
}
- else if ( (val = parse_boolean("md-clear", s, ss)) >= 0 )
+ else if ( (val = parse_boolean("md-clear", s, ss)) != -1 )
{
- opt_md_clear_pv = val;
- opt_md_clear_hvm = val;
+ switch ( val )
+ {
+ case 0:
+ case 1:
+ opt_md_clear_pv = opt_md_clear_hvm = val;
+ break;
+
+ case -2:
+ s += strlen("md-clear=");
+ if ( (val = parse_boolean("pv", s, ss)) >= 0 )
+ opt_md_clear_pv = val;
+ else if ( (val = parse_boolean("hvm", s, ss)) >= 0 )
+ opt_md_clear_hvm = val;
+ else
+ default:
+ rc = -EINVAL;
+ break;
+ }
}
/* Xen's speculative sidechannel mitigation settings. */
--
2.35.1
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