Re: [PATCH tip/master v2] kprobes: extable: Identify kprobes' insn-slots as kernel text area

Masami Hiramatsu
2016-12-27T06:24:21Z

Oops, I found I missed an rcu_read_unlock on the fast path...
I'll send v3.

Thanks,

On Tue, 27 Dec 2016 00:34:20 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Make __kernel_text_address()/kernel_text_address() returns
> true if the given address is on a kprobe's instruction slot,
> which is generated by kprobes as a trampoline code.
> This can help stacktraces to determine the address is on a
> text area or not.
>
> To implement this without any sleep in is_kprobe_*_slot(),
> this also modify insn_cache page list as a rcu list. It may
> increase processing deley (not processing time) for garbage
> slot collection, because it requires to wait an additional
> rcu grance period when freeing a page from the list.
> However, since it is not a hot path, we may not take care of it.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
>
> ---
> V2: Fix build error when CONFIG_KPROBES=n
>
> Hi Josh, could check this patch fixes your issue? It will
> enable unwinder code to validate return address by using
> __kernel_text_address() again.
> ---
> include/linux/kprobes.h | 22 ++++++++++++++-
> kernel/extable.c | 9 +++++-
> kernel/kprobes.c | 70 ++++++++++++++++++++++++++++++++++++-----------
> 3 files changed, 82 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 8f68490..f0496b0 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -281,6 +281,9 @@ struct kprobe_insn_cache {
> extern kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c);
> extern void __free_insn_slot(struct kprobe_insn_cache *c,
> kprobe_opcode_t *slot, int dirty);
> +/* sleep-less address checking routine */
> +extern bool __is_insn_slot_addr(struct kprobe_insn_cache *c,
> + unsigned long addr);
>
> #define DEFINE_INSN_CACHE_OPS(__name) \
> extern struct kprobe_insn_cache kprobe_##__name##_slots; \
> @@ -294,6 +297,11 @@ static inline void free_##__name##_slot(kprobe_opcode_t *slot, int dirty)\
> { \
> __free_insn_slot(&kprobe_##__name##_slots, slot, dirty); \
> } \
> + \
> +static inline bool is_kprobe_##__name##_slot(unsigned long addr) \
> +{ \
> + return __is_insn_slot_addr(&kprobe_##__name##_slots, addr); \
> +}
>
> DEFINE_INSN_CACHE_OPS(insn);
>
> @@ -330,7 +338,6 @@ extern int proc_kprobes_optimization_handler(struct ctl_table *table,
> int write, void __user *buffer,
> size_t *length, loff_t *ppos);
> #endif
> -
> #endif /* CONFIG_OPTPROBES */
> #ifdef CONFIG_KPROBES_ON_FTRACE
> extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> @@ -481,6 +488,19 @@ static inline int enable_jprobe(struct jprobe *jp)
> return enable_kprobe(&jp->kp);
> }
>
> +#ifndef CONFIG_KPROBES
> +static inline bool is_kprobe_insn_slot(unsigned long addr)
> +{
> + return false;
> +}
> +#endif
> +#ifndef CONFIG_OPTPROBES
> +static inline bool is_kprobe_optinsn_slot(unsigned long addr)
> +{
> + return false;
> +}
> +#endif
> +
> #ifdef CONFIG_KPROBES
> /*
> * Blacklist ganerating macro. Specify functions which is not probed
> diff --git a/kernel/extable.c b/kernel/extable.c
> index e820cce..81c9633 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -20,6 +20,7 @@
> #include <linux/module.h>
> #include <linux/mutex.h>
> #include <linux/init.h>
> +#include <linux/kprobes.h>
>
> #include <asm/sections.h>
> #include <asm/uaccess.h>
> @@ -104,6 +105,8 @@ int __kernel_text_address(unsigned long addr)
> return 1;
> if (is_ftrace_trampoline(addr))
> return 1;
> + if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
> + return 1;
> /*
> * There might be init symbols in saved stacktraces.
> * Give those symbols a chance to be printed in
> @@ -123,7 +126,11 @@ int kernel_text_address(unsigned long addr)
> return 1;
> if (is_module_text_address(addr))
> return 1;
> - return is_ftrace_trampoline(addr);
> + if (is_ftrace_trampoline(addr))
> + return 1;
> + if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
> + return 1;
> + return 0;
> }
>
> /*
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index d630954..1bd1c17 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -149,9 +149,11 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
> struct kprobe_insn_page *kip;
> kprobe_opcode_t *slot = NULL;
>
> + /* Since the slot array is not protected by rcu, we need a mutex */
> mutex_lock(&c->mutex);
> retry:
> - list_for_each_entry(kip, &c->pages, list) {
> + rcu_read_lock();
> + list_for_each_entry_rcu(kip, &c->pages, list) {
> if (kip->nused < slots_per_page(c)) {
> int i;
> for (i = 0; i < slots_per_page(c); i++) {
> @@ -167,6 +169,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
> WARN_ON(1);
> }
> }
> + rcu_read_unlock();
>
> /* If there are any garbage slots, collect it and try again. */
> if (c->nr_garbage && collect_garbage_slots(c) == 0)
> @@ -193,13 +196,15 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
> kip->nused = 1;
> kip->ngarbage = 0;
> kip->cache = c;
> - list_add(&kip->list, &c->pages);
> + list_add_rcu(&kip->list, &c->pages);
> slot = kip->insns;
> out:
> mutex_unlock(&c->mutex);
> return slot;
> }
>
> +
> +
> /* Return 1 if all garbages are collected, otherwise 0. */
> static int collect_one_slot(struct kprobe_insn_page *kip, int idx)
> {
> @@ -213,7 +218,8 @@ static int collect_one_slot(struct kprobe_insn_page *kip, int idx)
> * next time somebody inserts a probe.
> */
> if (!list_is_singular(&kip->list)) {
> - list_del(&kip->list);
> + list_del_rcu(&kip->list);
> + synchronize_rcu();
> kip->cache->free(kip->insns);
> kfree(kip);
> }
> @@ -248,29 +254,59 @@ void __free_insn_slot(struct kprobe_insn_cache *c,
> kprobe_opcode_t *slot, int dirty)
> {
> struct kprobe_insn_page *kip;
> + long idx;
>
> mutex_lock(&c->mutex);
> - list_for_each_entry(kip, &c->pages, list) {
> - long idx = ((long)slot - (long)kip->insns) /
> - (c->insn_size * sizeof(kprobe_opcode_t));
> - if (idx >= 0 && idx < slots_per_page(c)) {
> - WARN_ON(kip->slot_used[idx] != SLOT_USED);
> - if (dirty) {
> - kip->slot_used[idx] = SLOT_DIRTY;
> - kip->ngarbage++;
> - if (++c->nr_garbage > slots_per_page(c))
> - collect_garbage_slots(c);
> - } else
> - collect_one_slot(kip, idx);
> + rcu_read_lock();
> + list_for_each_entry_rcu(kip, &c->pages, list) {
> + idx = ((long)slot - (long)kip->insns) /
> + (c->insn_size * sizeof(kprobe_opcode_t));
> + if (idx >= 0 && idx < slots_per_page(c))
> goto out;
> - }
> }
> - /* Could not free this slot. */
> + /* Could not find this slot. */
> WARN_ON(1);
> + kip = NULL;
> out:
> + rcu_read_unlock();
> + /* Mark and sweep: this may sleep */
> + if (kip) {
> + /* Check double free */
> + WARN_ON(kip->slot_used[idx] != SLOT_USED);
> + if (dirty) {
> + kip->slot_used[idx] = SLOT_DIRTY;
> + kip->ngarbage++;
> + if (++c->nr_garbage > slots_per_page(c))
> + collect_garbage_slots(c);
> + } else
> + collect_one_slot(kip, idx);
> + }
> mutex_unlock(&c->mutex);
> }
>
> +/*
> + * Check given address is on the page of kprobe instruction slots.
> + * This will be used for checking whether the address on a stack
> + * is on a text area or not.
> + */
> +bool __is_insn_slot_addr(struct kprobe_insn_cache *c, unsigned long addr)
> +{
> + struct kprobe_insn_page *kip;
> + bool ret = false;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(kip, &c->pages, list) {
> + if (addr >= (unsigned long)kip->insns &&
> + addr < (unsigned long)kip->insns + PAGE_SIZE) {
> + ret = true;
> + break;
> + }
> + }
> + rcu_read_unlock();
> +
> + return ret;
> +}
> +
> #ifdef CONFIG_OPTPROBES
> /* For optimized_kprobe buffer */
> struct kprobe_insn_cache kprobe_optinsn_slots = {
>

--
Masami Hiramatsu <mhiramat@kernel.org>