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commit 693455c3c370e535eb6cd065800ff91e147815fa
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Tue Mar 5 11:58:04 2024 +0100
Commit: Jan Beulich <jbeulich@suse.com>
CommitDate: Tue Mar 5 11:58:04 2024 +0100

x86/spec: fix INDIRECT_THUNK option to only be set when build-enabled

Attempt to provide a more helpful error message when the user attempts to set
spec-ctrl=bti-thunk option but the support is build-time disabled.

While there also adjust the command line documentation to mention
CONFIG_INDIRECT_THUNK instead of INDIRECT_THUNK.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 8441fa806a3b778867867cd0159fa1722e90397e
master date: 2024-02-27 14:58:20 +0100
---
docs/misc/xen-command-line.pandoc | 10 +++++-----
xen/arch/x86/spec_ctrl.c | 7 ++++++-
2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 05f613c71c..2006697226 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2378,11 +2378,11 @@ guests to use.
performance reasons dom0 is unprotected by default. If it is necessary to
protect dom0 too, boot with `spec-ctrl=ibpb-entry`.

-If Xen was compiled with INDIRECT_THUNK support, `bti-thunk=` can be used to
-select which of the thunks gets patched into the `__x86_indirect_thunk_%reg`
-locations. The default thunk is `retpoline` (generally preferred), with the
-alternatives being `jmp` (a `jmp *%reg` gadget, minimal overhead), and
-`lfence` (an `lfence; jmp *%reg` gadget).
+If Xen was compiled with `CONFIG_INDIRECT_THUNK` support, `bti-thunk=` can be
+used to select which of the thunks gets patched into the
+`__x86_indirect_thunk_%reg` locations. The default thunk is `retpoline`
+(generally preferred), with the alternatives being `jmp` (a `jmp *%reg` gadget,
+minimal overhead), and `lfence` (an `lfence; jmp *%reg` gadget).

On hardware supporting IBRS (Indirect Branch Restricted Speculation), the
`ibrs=` option can be used to force or prevent Xen using the feature itself.
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 93f1cf3bb5..098fa3184d 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -253,7 +253,12 @@ static int __init cf_check parse_spec_ctrl(const char *s)
{
s += 10;

- if ( !cmdline_strcmp(s, "retpoline") )
+ if ( !IS_ENABLED(CONFIG_INDIRECT_THUNK) )
+ {
+ no_config_param("INDIRECT_THUNK", "spec-ctrl", s - 10, ss);
+ rc = -EINVAL;
+ }
+ else if ( !cmdline_strcmp(s, "retpoline") )
opt_thunk = THUNK_RETPOLINE;
else if ( !cmdline_strcmp(s, "lfence") )
opt_thunk = THUNK_LFENCE;
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.17