[PATCH v2 2/3] x86/spec: fix BRANCH_HARDEN option to only be set when build-enabled

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

The current logic to handle the BRANCH_HARDEN option will report it as enabled
even when build-time disabled. Fix this by only allowing the option to be set
when support for it is built into Xen.

Fixes: 2d6f36daa086 ('x86/nospec: Introduce CONFIG_SPECULATIVE_HARDEN_BRANCH')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v1:
 - Use no_config_param().
---
 xen/arch/x86/spec_ctrl.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 421fe3f640df..4ce8a7a0b8ef 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -50,7 +50,8 @@ static int8_t __initdata opt_psfd = -1;
 int8_t __ro_after_init opt_ibpb_ctxt_switch = -1;
 int8_t __read_mostly opt_eager_fpu = -1;
 int8_t __read_mostly opt_l1d_flush = -1;
-static bool __initdata opt_branch_harden = true;
+static bool __initdata opt_branch_harden =
+    IS_ENABLED(CONFIG_SPECULATIVE_HARDEN_BRANCH);
 
 bool __initdata bsp_delay_spec_ctrl;
 uint8_t __read_mostly default_xen_spec_ctrl;
@@ -268,7 +269,14 @@ static int __init cf_check parse_spec_ctrl(const char *s)
         else if ( (val = parse_boolean("l1d-flush", s, ss)) >= 0 )
             opt_l1d_flush = val;
         else if ( (val = parse_boolean("branch-harden", s, ss)) >= 0 )
+        {
+#ifdef CONFIG_SPECULATIVE_HARDEN_BRANCH
             opt_branch_harden = val;
+#else
+            no_config_param("SPECULATIVE_HARDEN_BRANCH", "spec-ctrl", s, ss);
+            rc = -EINVAL;
+#endif
+        }
         else if ( (val = parse_boolean("srb-lock", s, ss)) >= 0 )
             opt_srb_lock = val;
         else if ( (val = parse_boolean("unpriv-mmio", s, ss)) >= 0 )
-- 
2.43.0