livepatch: account for patch offset when applying NOP patch

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().

This requires livepatch_insn_len() to be called _after_ ->patch_offset
was set.

Fixes: 6974c75180f1 ("xen/x86: Livepatch: support patching CET-enhanced functions")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 8a87b9a0fb0564f9d68f0be0a0d1a17c34117b8b
master date: 2022-03-31 10:45:46 +0200

diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c
index e94ac9b228269bfeaf463b27d5e7b15b7129575e..a3cb63a7eadaf9b73e1297261d14171af3de1449 100644 (file)
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -144,9 +144,6 @@ void noinline arch_livepatch_apply(struct livepatch_func *func)
 
     func->patch_offset = 0;
     old_ptr = func->old_addr;
-    len = livepatch_insn_len(func);
-    if ( !len )
-        return;
 
     /*
      * CET hotpatching support: We may have functions starting with an ENDBR64
@@ -159,6 +156,11 @@ void noinline arch_livepatch_apply(struct livepatch_func *func)
     if ( is_endbr64(old_ptr) )
         func->patch_offset += ENDBR64_LEN;
 
+    /* This call must be done with ->patch_offset already set. */
+    len = livepatch_insn_len(func);
+    if ( !len )
+        return;
+
     memcpy(func->opaque, old_ptr + func->patch_offset, len);
     if ( func->new_addr )
     {

diff --git a/xen/include/xen/livepatch.h b/xen/include/xen/livepatch.h
index f3ae10f007ede935333af14472a24c5be31119ad..9fdb29c382b6ee5dc4643edf12b6dd3e929c848f 100644 (file)
--- 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;
 }