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authorMasami Hiramatsu <mhiramat@kernel.org>2017-01-08 23:58:09 +0900
committerIngo Molnar <mingo@kernel.org>2017-01-14 08:38:05 +0100
commit5b485629ba0d5d027880769ff467c587b24b4bde (patch)
tree395ec5583989fd297007dfd2c7d04292ed273242 /kernel/kprobes.c
parentf913f3a655cb4c37129bb36c9f175071e1fbdc29 (diff)
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kprobes, extable: Identify kprobes trampolines as kernel text area
Improve __kernel_text_address()/kernel_text_address() to return true if the given address is on a kprobe's instruction slot trampoline. This can help stacktraces to determine the address is on a text area or not. To implement this atomically in is_kprobe_*_slot(), also change the insn_cache page list to an RCU list. This changes timings a bit (it delays page freeing to the RCU garbage collection phase), but none of that is in the hot path. Note: this change can add small overhead to stack unwinders because it adds 2 additional checks to __kernel_text_address(). However, the impact should be very small, because kprobe_insn_pages list has 1 entry per 256 probes(on x86, on arm/arm64 it will be 1024 probes), and kprobe_optinsn_pages has 1 entry per 32 probes(on x86). In most use cases, the number of kprobe events may be less than 20, which means that is_kprobe_*_slot() will check just one entry. Tested-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrey Konovalov <andreyknvl@google.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/148388747896.6869.6354262871751682264.stgit@devbox [ Improved the changelog and coding style. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/kprobes.c')
-rw-r--r--kernel/kprobes.c73
1 files changed, 54 insertions, 19 deletions
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 43460104f119..ebb4dadca66b 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++) {
@@ -159,6 +161,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
kip->slot_used[i] = SLOT_USED;
kip->nused++;
slot = kip->insns + (i * c->insn_size);
+ rcu_read_unlock();
goto out;
}
}
@@ -167,6 +170,7 @@ 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)
@@ -193,7 +197,7 @@ 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);
@@ -213,7 +217,8 @@ 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);
}
@@ -235,8 +240,7 @@ static int collect_garbage_slots(struct kprobe_insn_cache *c)
continue;
kip->ngarbage = 0; /* we will collect all garbages */
for (i = 0; i < slots_per_page(c); i++) {
- if (kip->slot_used[i] == SLOT_DIRTY &&
- collect_one_slot(kip, i))
+ if (kip->slot_used[i] == SLOT_DIRTY && collect_one_slot(kip, i))
break;
}
}
@@ -248,29 +252,60 @@ 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 = {