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Date: Mon, 9 Nov 2015 10:16:05 -0600
From: Chris J Arges <chris.j.arges@...onical.com>
To: live-patching@...r.kernel.org
Cc: jeyu@...hat.com, Chris J Arges <chris.j.arges@...onical.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Seth Jennings <sjenning@...hat.com>,
Jiri Kosina <jikos@...nel.org>,
Vojtech Pavlik <vojtech@...e.com>, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs directory
In cases of duplicate symbols in vmlinux, old_sympos will be used to
disambiguate instead of old_addr. Normally old_sympos will be 0, and
default to only returning the first found instance of that symbol. If an
incorrect symbol position is specified then livepatching will fail.
Finally, old_addr is now an internal structure element and not to be
specified by the user.
The following directory structure will allow for cases when the same
function name exists in a single object.
/sys/kernel/livepatch/<patch>/<object>/<function.number>
The number corresponds to the nth occurrence of the symbol name in
kallsyms for the patched object.
An example of patching multiple symbols can be found here:
https://github.com/dynup/kpatch/issues/493
Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>
---
Documentation/ABI/testing/sysfs-kernel-livepatch | 6 ++-
include/linux/livepatch.h | 20 ++++---
kernel/livepatch/core.c | 66 ++++++++++++++++--------
3 files changed, 61 insertions(+), 31 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
index 5bf42a8..21b6bc1 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -33,7 +33,7 @@ Description:
The object directory contains subdirectories for each function
that is patched within the object.
-What: /sys/kernel/livepatch/<patch>/<object>/<function>
+What: /sys/kernel/livepatch/<patch>/<object>/<function,number>
Date: Nov 2014
KernelVersion: 3.19.0
Contact: live-patching@...r.kernel.org
@@ -41,4 +41,8 @@ Description:
The function directory contains attributes regarding the
properties and state of the patched function.
+ The directory name contains the patched function name and a
+ number corresponding to the nth occurrence of the symbol name
+ in kallsyms for the patched object.
+
There are currently no such attributes.
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 31db7a0..986e06d 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
+ * @old_sympos: a hint indicating which symbol position the old function
* can be found (optional, vmlinux patches only)
+ * @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
@@ -47,17 +48,20 @@ struct klp_func {
/* external */
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 the vmlinux object. If this information is not
+ * present, the first symbol located with kallsyms is used. This value
+ * corresponds to the nth occurrence of the symbol name in kallsyms for
+ * the patched object. If the name is not unique and old_sympos is not
+ * provided, the patch application fails as there is no way to resolve
+ * the ambiguity.
*/
- 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..1dd0d44 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -142,6 +142,7 @@ struct klp_find_arg {
* name in the same object.
*/
unsigned long count;
+ unsigned long pos;
};
static int klp_find_callback(void *data, const char *name,
@@ -166,28 +167,39 @@ static int klp_find_callback(void *data, const char *name,
args->addr = addr;
args->count++;
+ /*
+ * ensure count matches the symbol position
+ */
+ if (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 *addr, unsigned long sympos)
{
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, then check that 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)
- pr_err("unresolvable ambiguity (%lu matches) on symbol '%s' in object '%s'\n",
- args.count, name, objname);
+ else if (sympos != (args.count - 1))
+ 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;
@@ -239,20 +251,19 @@ static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr)
static int klp_find_verify_func_addr(struct klp_object *obj,
struct klp_func *func)
{
+ int sympos = 0;
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_sympos && !klp_is_module(obj))
+ sympos = func->old_sympos;
- 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);
+ /*
+ * Verify the symbol, find old_addr, and write it to the structure.
+ * By default sympos will be 0 and thus will only look for the first
+ * occurrence. If another value is specified then that will be used.
+ */
+ ret = klp_find_object_symbol(obj->name, func->old_name,
+ &func->old_addr, sympos);
return ret;
}
@@ -277,7 +288,7 @@ 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);
+ return klp_find_object_symbol(pmod->name, name, addr, 0);
}
static int klp_write_object_relocations(struct module *pmod,
@@ -307,7 +318,7 @@ static int klp_write_object_relocations(struct module *pmod,
else
ret = klp_find_object_symbol(obj->mod->name,
reloc->name,
- &reloc->val);
+ &reloc->val, 0);
if (ret)
return ret;
}
@@ -587,7 +598,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
* /sys/kernel/livepatch/<patch>
* /sys/kernel/livepatch/<patch>/enabled
* /sys/kernel/livepatch/<patch>/<object>
- * /sys/kernel/livepatch/<patch>/<object>/<func>
+ * /sys/kernel/livepatch/<patch>/<object>/<func,number>
*/
static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
@@ -732,8 +743,7 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
INIT_LIST_HEAD(&func->stack_node);
func->state = KLP_DISABLED;
- return kobject_init_and_add(&func->kobj, &klp_ktype_func,
- &obj->kobj, "%s", func->old_name);
+ return 0;
}
/* parts of the initialization that is done only when the object is loaded */
@@ -755,6 +765,18 @@ static int klp_init_object_loaded(struct klp_patch *patch,
return ret;
}
+ /*
+ * for each function initialize and add, old_sympos will be already
+ * verified at this point
+ */
+ klp_for_each_func(obj, func) {
+ ret = kobject_init_and_add(&func->kobj, &klp_ktype_func,
+ &obj->kobj, "%s,%lu", func->old_name,
+ func->old_sympos ? func->old_sympos : 0);
+ if (ret)
+ return ret;
+ }
+
return 0;
}
--
1.9.1
--
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