[PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field to klp_reloc

[Chris J Arges <chris.j.arges@canonical.com>]

In cases of duplicate symbols, sympos will be used to disambiguate instead
of val. By default old_sympos will be 0, and patching will only succeed if
the symbol is unique. Specifying a positive value will ensure that
occurrence of the symbol will be used for patching if it is valid.

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
---
 include/linux/livepatch.h |  5 ++--
 kernel/livepatch/core.c   | 74 ++++++++++-------------------------------------
 2 files changed, 18 insertions(+), 61 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index df7b752..fb968a2 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -68,8 +68,8 @@ struct klp_func {
 /**
  * struct klp_reloc - relocation structure for live patching
  * @loc:	address where the relocation will be written
- * @val:	address of the referenced symbol (optional,
- *		vmlinux	patches only)
+ * @val:	address of the referenced symbol
+ * @sympos:     position in kallsyms to disambiguate symbols (optional)
  * @type:	ELF relocation type
  * @name:	name of the referenced symbol (for lookup/verification)
  * @addend:	offset from the referenced symbol
@@ -78,6 +78,7 @@ struct klp_func {
 struct klp_reloc {
 	unsigned long loc;
 	unsigned long val;
+	unsigned long sympos;
 	unsigned long type;
 	const char *name;
 	int addend;
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 26f9778..4eb8691 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -207,45 +207,6 @@ static int klp_find_object_symbol(const char *objname, const char *name,
 	return -EINVAL;
 }
 
-struct klp_verify_args {
-	const char *name;
-	const unsigned long addr;
-};
-
-static int klp_verify_callback(void *data, const char *name,
-			       struct module *mod, unsigned long addr)
-{
-	struct klp_verify_args *args = data;
-
-	if (!mod &&
-	    !strcmp(args->name, name) &&
-	    args->addr == addr)
-		return 1;
-
-	return 0;
-}
-
-static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr)
-{
-	struct klp_verify_args args = {
-		.name = name,
-		.addr = addr,
-	};
-	int ret;
-
-	mutex_lock(&module_mutex);
-	ret = kallsyms_on_each_symbol(klp_verify_callback, &args);
-	mutex_unlock(&module_mutex);
-
-	if (!ret) {
-		pr_err("symbol '%s' not found at specified address 0x%016lx, kernel mismatch?\n",
-			name, addr);
-		return -EINVAL;
-	}
-
-	return 0;
-}
-
 static int klp_find_verify_func_addr(struct klp_object *obj,
 				     struct klp_func *func)
 {
@@ -261,7 +222,7 @@ static int klp_find_verify_func_addr(struct klp_object *obj,
  * object is either vmlinux or the kmod being patched).
  */
 static int klp_find_external_symbol(struct module *pmod, const char *name,
-				    unsigned long *addr)
+				    unsigned long *addr, unsigned long sympos)
 {
 	const struct kernel_symbol *sym;
 
@@ -276,7 +237,7 @@ static int klp_find_external_symbol(struct module *pmod, const char *name,
 	preempt_enable();
 
 	/* otherwise check if it's in another .o within the patch module */
-	return klp_find_object_symbol(pmod->name, name, addr, 0);
+	return klp_find_object_symbol(pmod->name, name, addr, sympos);
 }
 
 static int klp_write_object_relocations(struct module *pmod,
@@ -292,24 +253,19 @@ static int klp_write_object_relocations(struct module *pmod,
 		return -EINVAL;
 
 	for (reloc = obj->relocs; reloc->name; reloc++) {
-		if (!klp_is_module(obj)) {
-			ret = klp_verify_vmlinux_symbol(reloc->name,
-							reloc->val);
-			if (ret)
-				return ret;
-		} else {
-			/* module, reloc->val needs to be discovered */
-			if (reloc->external)
-				ret = klp_find_external_symbol(pmod,
-							       reloc->name,
-							       &reloc->val);
-			else
-				ret = klp_find_object_symbol(obj->mod->name,
-							     reloc->name,
-							     &reloc->val, 0);
-			if (ret)
-				return ret;
-		}
+		/* reloc->val needs to be discovered */
+		if (reloc->external)
+			ret = klp_find_external_symbol(pmod,
+						       reloc->name,
+						       &reloc->val,
+						       reloc->sympos);
+		else
+			ret = klp_find_object_symbol(obj->mod->name,
+						     reloc->name,
+						     &reloc->val,
+						     reloc->sympos);
+		if (ret)
+			return ret;
 		ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
 					     reloc->val + reloc->addend);
 		if (ret) {
-- 
1.9.1