When converting indirect to direct calls, there is no need to execute endbr64
instructions. Detect and optimise this case, leaving a warning in the case
that no endbr64 was found, as it likely indicates a build error.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
Reviewed-by: Jan Beulich <jbeul...@suse.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>
---
xen/arch/x86/alternative.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
index ec24692e9595..65537fe1f0bd 100644
--- a/xen/arch/x86/alternative.c
+++ b/xen/arch/x86/alternative.c
@@ -18,6 +18,7 @@
#include <xen/delay.h>
#include <xen/types.h>
#include <asm/apic.h>
+#include <asm/endbr.h>
#include <asm/processor.h>
#include <asm/alternative.h>
#include <xen/init.h>
@@ -279,6 +280,28 @@ static void init_or_livepatch _apply_alternatives(struct
alt_instr *start,
if ( dest )
{
+ /*
+ * When building for CET-IBT, all function pointer targets
+ * should have an endbr64 instruction.
+ *
+ * If this is not the case, leave a warning because
+ * something is probably wrong with the build. A CET-IBT
+ * enabled system might have exploded already.
+ *
+ * Otherwise, skip the endbr64 instruction. This is a
+ * marginal perf improvement which saves on instruction
+ * decode bandwidth.
+ */
+ if ( IS_ENABLED(CONFIG_HAS_CC_CET_IBT) )
+ {
+ if ( is_endbr64(dest) )
+ dest += 4;
+ else
+ printk(XENLOG_WARNING
+ "altcall %ps dest %ps has no endbr64\n",
+ orig, dest);
+ }
+
disp = dest - (orig + 5);
ASSERT(disp == (int32_t)disp);
*(int32_t *)(buf + 1) = disp;
--
2.11.0
