[PATCH] livepatch: account for patch offset when applying NOP patch

[Jan Beulich]

While not triggered by the trivial xen_nop in-tree patch on
staging/master, that patch exposes a problem on the stable trees, where
all functions have ENDBR inserted. When NOP-ing out a range, we need to
account for this. Handle this right in livepatch_insn_len().

Fixes: 6974c75180f1 ("xen/x86: Livepatch: support patching CET-enhanced 
functions")
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
Only build tested, as I don't have a live patching environment available.

For Arm this assumes that the patch_offset field starts out as zero; I
think we can make such an assumption, yet otoh on x86 explicit
initialization was added by the cited commit.

--- a/xen/include/xen/livepatch.h
+++ b/xen/include/xen/livepatch.h
@@ -90,7 +90,7 @@ static inline
 unsigned int livepatch_insn_len(const struct livepatch_func *func)
 {
     if ( !func->new_addr )
-        return func->new_size;
+        return func->new_size - func->patch_offset;
 
     return ARCH_PATCH_INSN_SIZE;
 }