[PATCH] x86/alternatives: fix .init section reference in _apply_alternatives()

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

The code in _apply_alternatives() will unconditionally attempt to read
__initdata_cf_clobber_{start,end} when called as part of applying alternatives
to a livepatch payload.  That leads to a page-fault as
__initdata_cf_clobber_{start,end} living in .init section will have been
unmapped by the time a livepatch gets loaded.

Fix by adding a check that limits the clobbering of endbr64 instructions to
boot time only.

Fixes: 37ed5da851b8 ('x86/altcall: Optimise away endbr64 instruction where 
possible')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/alternative.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
index 21af0e825822..2e7ba6e0b833 100644
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -326,7 +326,7 @@ static void init_or_livepatch _apply_alternatives(struct 
alt_instr *start,
      * Clobber endbr64 instructions now that altcall has finished optimising
      * all indirect branches to direct ones.
      */
-    if ( force && cpu_has_xen_ibt )
+    if ( force && cpu_has_xen_ibt && system_state < SYS_STATE_active )
     {
         void *const *val;
         unsigned int clobbered = 0;
-- 
2.44.0