linux/kernel/livepatch/patch.c at multikernel-riscv · multikernel/linux · GitHub

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// SPDX-License-Identifier: GPL-2.0-or-later

* patch.c - livepatch patching functions

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/livepatch.h>

#include <linux/list.h>

#include <linux/ftrace.h>

#include <linux/rculist.h>

#include <linux/slab.h>

#include <linux/bug.h>

#include <linux/printk.h>

#include "core.h"

#include "patch.h"

#include "transition.h"

static LIST_HEAD(klp_ops);

struct klp_ops *klp_find_ops(void *old_func)

{

struct klp_ops *ops;

struct klp_func *func;

list_for_each_entry(ops, &klp_ops, node) {

func = list_first_entry(&ops->func_stack, struct klp_func,

stack_node);

if (func->old_func == old_func)

return ops;

}

return NULL;

}

static void notrace klp_ftrace_handler(unsigned long ip,

unsigned long parent_ip,

struct ftrace_ops *fops,

struct ftrace_regs *fregs)

{

struct klp_ops *ops;

struct klp_func *func;

int patch_state;

int bit;

ops = container_of(fops, struct klp_ops, fops);

* The ftrace_test_recursion_trylock() will disable preemption,

* which is required for the variant of synchronize_rcu() that is

* used to allow patching functions where RCU is not watching.

* See klp_synchronize_transition() for more details.

bit = ftrace_test_recursion_trylock(ip, parent_ip);

if (WARN_ON_ONCE(bit < 0))

return;

func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,

stack_node);

* func should never be NULL because preemption should be disabled here

* and unregister_ftrace_function() does the equivalent of a

* synchronize_rcu() before the func_stack removal.

if (WARN_ON_ONCE(!func))

goto unlock;

* In the enable path, enforce the order of the ops->func_stack and

* func->transition reads. The corresponding write barrier is in

* __klp_enable_patch().

* (Note that this barrier technically isn't needed in the disable

* path. In the rare case where klp_update_patch_state() runs before

* this handler, its TIF_PATCH_PENDING read and this func->transition

* read need to be ordered. But klp_update_patch_state() already

* enforces that.)

smp_rmb();

if (unlikely(func->transition)) {

* Enforce the order of the func->transition and

* current->patch_state reads. Otherwise we could read an

* out-of-date task state and pick the wrong function. The

* corresponding write barrier is in klp_init_transition().

smp_rmb();

patch_state = current->patch_state;

WARN_ON_ONCE(patch_state == KLP_TRANSITION_IDLE);

if (patch_state == KLP_TRANSITION_UNPATCHED) {

* Use the previously patched version of the function.

* If no previous patches exist, continue with the

* original function.

func = list_entry_rcu(func->stack_node.next,

struct klp_func, stack_node);

if (&func->stack_node == &ops->func_stack)

goto unlock;

}

* NOPs are used to replace existing patches with original code.

* Do nothing! Setting pc would cause an infinite loop.

if (func->nop)

goto unlock;

ftrace_regs_set_instruction_pointer(fregs, (unsigned long)func->new_func);

unlock:

ftrace_test_recursion_unlock(bit);

}

static void klp_unpatch_func(struct klp_func *func)

{

struct klp_ops *ops;

if (WARN_ON(!func->patched))

return;

if (WARN_ON(!func->old_func))

return;

ops = klp_find_ops(func->old_func);

if (WARN_ON(!ops))

return;

if (list_is_singular(&ops->func_stack)) {

unsigned long ftrace_loc;

ftrace_loc = ftrace_location((unsigned long)func->old_func);

if (WARN_ON(!ftrace_loc))

return;

WARN_ON(unregister_ftrace_function(&ops->fops));

WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));

list_del_rcu(&func->stack_node);

list_del(&ops->node);

kfree(ops);

} else {

list_del_rcu(&func->stack_node);

}

func->patched = false;

}

static int klp_patch_func(struct klp_func *func)

{

struct klp_ops *ops;

int ret;

if (WARN_ON(!func->old_func))

return -EINVAL;

if (WARN_ON(func->patched))

return -EINVAL;

ops = klp_find_ops(func->old_func);

if (!ops) {

unsigned long ftrace_loc;

ftrace_loc = ftrace_location((unsigned long)func->old_func);

if (!ftrace_loc) {

pr_err("failed to find location for function '%s'\n",

func->old_name);

return -EINVAL;

}

ops = kzalloc_obj(*ops);

if (!ops)

return -ENOMEM;

ops->fops.func = klp_ftrace_handler;

ops->fops.flags = FTRACE_OPS_FL_DYNAMIC |

#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS

FTRACE_OPS_FL_SAVE_REGS |

#endif

FTRACE_OPS_FL_IPMODIFY |

FTRACE_OPS_FL_PERMANENT;

list_add(&ops->node, &klp_ops);

INIT_LIST_HEAD(&ops->func_stack);

list_add_rcu(&func->stack_node, &ops->func_stack);

ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);

if (ret) {

pr_err("failed to set ftrace filter for function '%s' (%d)\n",

func->old_name, ret);

goto err;

}

ret = register_ftrace_function(&ops->fops);

if (ret) {

pr_err("failed to register ftrace handler for function '%s' (%d)\n",

func->old_name, ret);

ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);

goto err;

}

} else {

list_add_rcu(&func->stack_node, &ops->func_stack);

}

func->patched = true;

return 0;

err:

list_del_rcu(&func->stack_node);

list_del(&ops->node);

kfree(ops);

return ret;

}

static void __klp_unpatch_object(struct klp_object *obj, bool nops_only)

{

struct klp_func *func;

klp_for_each_func(obj, func) {

if (nops_only && !func->nop)

continue;

if (func->patched)

klp_unpatch_func(func);

}

if (obj->dynamic || !nops_only)

obj->patched = false;

}

void klp_unpatch_object(struct klp_object *obj)

{

__klp_unpatch_object(obj, false);

}

int klp_patch_object(struct klp_object *obj)

{

struct klp_func *func;

int ret;

if (WARN_ON(obj->patched))

return -EINVAL;

klp_for_each_func(obj, func) {

ret = klp_patch_func(func);

if (ret) {

klp_unpatch_object(obj);

return ret;

}

obj->patched = true;

return 0;

}

static void __klp_unpatch_objects(struct klp_patch *patch, bool nops_only)

{

struct klp_object *obj;

klp_for_each_object(patch, obj)

if (obj->patched)

__klp_unpatch_object(obj, nops_only);

}

void klp_unpatch_objects(struct klp_patch *patch)

{

__klp_unpatch_objects(patch, false);

}

void klp_unpatch_objects_dynamic(struct klp_patch *patch)

{

__klp_unpatch_objects(patch, true);

}

linux/kernel/livepatch/patch.c at multikernel-riscv · multikernel/linux · GitHub

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