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Subject[PATCH 1/3 v7] livepatch: add old_sympos as disambiguator field to klp_func
Date
In cases of duplicate symbols, old_sympos will be used to disambiguate
instead of old_addr. 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 in kallsyms for the patched object
will be used for patching if it is valid.

In addition, make old_addr an internal structure field not to be specified
by the user. Finally, remove klp_find_verify_func_addr as it can be
replaced by klp_find_object_symbol directly.

Support for symbol position disambiguation for relocations is added in the
next patch in this series.

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
---
include/linux/livepatch.h | 19 +++++++------
kernel/livepatch/core.c | 72 ++++++++++++++++++++---------------------------
2 files changed, 41 insertions(+), 50 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 31db7a0..b60e8ab 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -37,8 +37,9 @@ enum klp_state {
* struct klp_func - function structure for live patching
* @old_name: name of the function to be patched
* @new_func: pointer to the patched function code
- * @old_addr: a hint conveying at what address the old function
- * can be found (optional, vmlinux patches only)
+ * @old_sympos: a hint indicating which symbol position the old function
+ * can be found (optional)
+ * @old_addr: the address of the function being patched
* @kobj: kobject for sysfs resources
* @state: tracks function-level patch application state
* @stack_node: list node for klp_ops func_stack list
@@ -48,16 +49,16 @@ struct klp_func {
const char *old_name;
void *new_func;
/*
- * The old_addr field is optional and can be used to resolve
- * duplicate symbol names in the vmlinux object. If this
- * information is not present, the symbol is located by name
- * with kallsyms. If the name is not unique and old_addr is
- * not provided, the patch application fails as there is no
- * way to resolve the ambiguity.
+ * The old_sympos field is optional and can be used to resolve
+ * duplicate symbol names in livepatch objects. If this field is zero,
+ * it is expected the symbol is unique, otherwise patching fails. If
+ * this value is greater than zero then that occurrence of the symbol
+ * in kallsyms for the given object is used.
*/
- unsigned long old_addr;
+ unsigned long old_sympos;

/* internal */
+ unsigned long old_addr;
struct kobject kobj;
enum klp_state state;
struct list_head stack_node;
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6e53441..5a53383 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -135,13 +135,8 @@ struct klp_find_arg {
const char *objname;
const char *name;
unsigned long addr;
- /*
- * If count == 0, the symbol was not found. If count == 1, a unique
- * match was found and addr is set. If count > 1, there is
- * unresolvable ambiguity among "count" number of symbols with the same
- * name in the same object.
- */
unsigned long count;
+ unsigned long pos;
};

static int klp_find_callback(void *data, const char *name,
@@ -158,37 +153,48 @@ static int klp_find_callback(void *data, const char *name,
if (args->objname && strcmp(args->objname, mod->name))
return 0;

- /*
- * args->addr might be overwritten if another match is found
- * but klp_find_object_symbol() handles this and only returns the
- * addr if count == 1.
- */
args->addr = addr;
args->count++;

+ /*
+ * Finish the search when the symbol is found for the desired position
+ * or the position is not defined for a non-unique symbol.
+ */
+ if ((args->pos && (args->count == args->pos)) ||
+ (!args->pos && (args->count > 1)))
+ return 1;
+
return 0;
}

static int klp_find_object_symbol(const char *objname, const char *name,
- unsigned long *addr)
+ unsigned long sympos, unsigned long *addr)
{
struct klp_find_arg args = {
.objname = objname,
.name = name,
.addr = 0,
- .count = 0
+ .count = 0,
+ .pos = sympos,
};

mutex_lock(&module_mutex);
kallsyms_on_each_symbol(klp_find_callback, &args);
mutex_unlock(&module_mutex);

- if (args.count == 0)
+ /*
+ * Ensure an address was found. If sympos is 0, ensure symbol is unique;
+ * otherwise ensure the symbol position count matches sympos.
+ */
+ if (args.addr == 0)
pr_err("symbol '%s' not found in symbol table\n", name);
- else if (args.count > 1)
+ else if (args.count > 1 && sympos == 0) {
pr_err("unresolvable ambiguity (%lu matches) on symbol '%s' in object '%s'\n",
args.count, name, objname);
- else {
+ } else if (sympos != args.count && sympos > 0) {
+ pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
+ sympos, name, objname ? objname : "vmlinux");
+ } else {
*addr = args.addr;
return 0;
}
@@ -236,27 +242,6 @@ static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr)
return 0;
}

-static int klp_find_verify_func_addr(struct klp_object *obj,
- struct klp_func *func)
-{
- int ret;
-
-#if defined(CONFIG_RANDOMIZE_BASE)
- /* If KASLR has been enabled, adjust old_addr accordingly */
- if (kaslr_enabled() && func->old_addr)
- func->old_addr += kaslr_offset();
-#endif
-
- if (!func->old_addr || klp_is_module(obj))
- ret = klp_find_object_symbol(obj->name, func->old_name,
- &func->old_addr);
- else
- ret = klp_verify_vmlinux_symbol(func->old_name,
- func->old_addr);
-
- return ret;
-}
-
/*
* external symbols are located outside the parent object (where the parent
* object is either vmlinux or the kmod being patched).
@@ -276,8 +261,11 @@ 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);
+ /*
+ * Check if it's in another .o within the patch module. This also
+ * checks that the external symbol is unique.
+ */
+ return klp_find_object_symbol(pmod->name, name, 0, addr);
}

static int klp_write_object_relocations(struct module *pmod,
@@ -307,7 +295,7 @@ static int klp_write_object_relocations(struct module *pmod,
else
ret = klp_find_object_symbol(obj->mod->name,
reloc->name,
- &reloc->val);
+ 0, &reloc->val);
if (ret)
return ret;
}
@@ -750,7 +738,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
}

klp_for_each_func(obj, func) {
- ret = klp_find_verify_func_addr(obj, func);
+ ret = klp_find_object_symbol(obj->name, func->old_name,
+ func->old_sympos,
+ &func->old_addr);
if (ret)
return ret;
}
--
1.9.1


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