Mailing List Archive

commit a482be921144493a344d9ec0a904ccb71657506f
Author: Roger Pau Monné <roger.pau@citrix.com>
AuthorDate: Tue Apr 9 14:50:46 2024 +0200
Commit: Andrew Cooper <andrew.cooper3@citrix.com>
CommitDate: Tue Apr 9 16:45:01 2024 +0100

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

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 when Xen is using IBT.

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@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
(cherry picked from commit 4be1fef1e6572c2be0bd378902ffb62a6e73faeb)
---
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 21af0e8258..2e7ba6e0b8 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;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18