* [PATCH 1/2] kprobes: Remove NMI context check
@ 2020-12-10 15:30 Masami Hiramatsu
2020-12-10 15:31 ` [PATCH 2/2] kprobes: Tell lockdep about kprobe nesting Masami Hiramatsu
2020-12-11 14:47 ` [PATCH 1/2] kprobes: Remove NMI context check Greg KH
0 siblings, 2 replies; 3+ messages in thread
From: Masami Hiramatsu @ 2020-12-10 15:30 UTC (permalink / raw)
To: stable
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H . Peter Anvin, linux-kernel, Naveen N . Rao,
Anil S Keshavamurthy, David S . Miller, Masami Hiramatsu,
Solar Designer, Eddy_Wu, Peter Zijlstra
commit e03b4a084ea6b0a18b0e874baec439e69090c168 upstream.
The in_nmi() check in pre_handler_kretprobe() is meant to avoid
recursion, and blindly assumes that anything NMI is recursive.
However, since commit:
9b38cc704e84 ("kretprobe: Prevent triggering kretprobe from within kprobe_flush_task")
there is a better way to detect and avoid actual recursion.
By setting a dummy kprobe, any actual exceptions will terminate early
(by trying to handle the dummy kprobe), and recursion will not happen.
Employ this to avoid the kretprobe_table_lock() recursion, replacing
the over-eager in_nmi() check.
Cc: stable@vger.kernel.org # 5.9.x
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/159870615628.1229682.6087311596892125907.stgit@devnote2
---
kernel/kprobes.c | 16 ++++------------
1 file changed, 4 insertions(+), 12 deletions(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index e995541d277d..b885d884603d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1359,7 +1359,8 @@ static void cleanup_rp_inst(struct kretprobe *rp)
struct hlist_node *next;
struct hlist_head *head;
- /* No race here */
+ /* To avoid recursive kretprobe by NMI, set kprobe busy here */
+ kprobe_busy_begin();
for (hash = 0; hash < KPROBE_TABLE_SIZE; hash++) {
kretprobe_table_lock(hash, &flags);
head = &kretprobe_inst_table[hash];
@@ -1369,6 +1370,8 @@ static void cleanup_rp_inst(struct kretprobe *rp)
}
kretprobe_table_unlock(hash, &flags);
}
+ kprobe_busy_end();
+
free_rp_inst(rp);
}
NOKPROBE_SYMBOL(cleanup_rp_inst);
@@ -1937,17 +1940,6 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
unsigned long hash, flags = 0;
struct kretprobe_instance *ri;
- /*
- * To avoid deadlocks, prohibit return probing in NMI contexts,
- * just skip the probe and increase the (inexact) 'nmissed'
- * statistical counter, so that the user is informed that
- * something happened:
- */
- if (unlikely(in_nmi())) {
- rp->nmissed++;
- return 0;
- }
-
/* TODO: consider to only swap the RA after the last pre_handler fired */
hash = hash_ptr(current, KPROBE_HASH_BITS);
raw_spin_lock_irqsave(&rp->lock, flags);
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH 2/2] kprobes: Tell lockdep about kprobe nesting
2020-12-10 15:30 [PATCH 1/2] kprobes: Remove NMI context check Masami Hiramatsu
@ 2020-12-10 15:31 ` Masami Hiramatsu
2020-12-11 14:47 ` [PATCH 1/2] kprobes: Remove NMI context check Greg KH
1 sibling, 0 replies; 3+ messages in thread
From: Masami Hiramatsu @ 2020-12-10 15:31 UTC (permalink / raw)
To: stable
Cc: Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H . Peter Anvin, linux-kernel, Naveen N . Rao,
Anil S Keshavamurthy, David S . Miller, Masami Hiramatsu,
Solar Designer, Eddy_Wu, Peter Zijlstra
From: Steven Rostedt (VMware) <rostedt@goodmis.org>
commit 645f224e7ba2f4200bf163153d384ceb0de5462e upstream.
Since the kprobe handlers have protection that prohibits other handlers from
executing in other contexts (like if an NMI comes in while processing a
kprobe, and executes the same kprobe, it will get fail with a "busy"
return). Lockdep is unaware of this protection. Use lockdep's nesting api to
differentiate between locks taken in INT3 context and other context to
suppress the false warnings.
Link: https://lore.kernel.org/r/20201102160234.fa0ae70915ad9e2b21c08b85@kernel.org
Cc: stable@vger.kernel.org # 5.9.x
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/kprobes.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index b885d884603d..1b7fd1ab8ddc 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1250,7 +1250,13 @@ __acquires(hlist_lock)
*head = &kretprobe_inst_table[hash];
hlist_lock = kretprobe_table_lock_ptr(hash);
- raw_spin_lock_irqsave(hlist_lock, *flags);
+ /*
+ * Nested is a workaround that will soon not be needed.
+ * There's other protections that make sure the same lock
+ * is not taken on the same CPU that lockdep is unaware of.
+ * Differentiate when it is taken in NMI context.
+ */
+ raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi());
}
NOKPROBE_SYMBOL(kretprobe_hash_lock);
@@ -1259,7 +1265,13 @@ static void kretprobe_table_lock(unsigned long hash,
__acquires(hlist_lock)
{
raw_spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
- raw_spin_lock_irqsave(hlist_lock, *flags);
+ /*
+ * Nested is a workaround that will soon not be needed.
+ * There's other protections that make sure the same lock
+ * is not taken on the same CPU that lockdep is unaware of.
+ * Differentiate when it is taken in NMI context.
+ */
+ raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi());
}
NOKPROBE_SYMBOL(kretprobe_table_lock);
@@ -1942,7 +1954,12 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
/* TODO: consider to only swap the RA after the last pre_handler fired */
hash = hash_ptr(current, KPROBE_HASH_BITS);
- raw_spin_lock_irqsave(&rp->lock, flags);
+ /*
+ * Nested is a workaround that will soon not be needed.
+ * There's other protections that make sure the same lock
+ * is not taken on the same CPU that lockdep is unaware of.
+ */
+ raw_spin_lock_irqsave_nested(&rp->lock, flags, 1);
if (!hlist_empty(&rp->free_instances)) {
ri = hlist_entry(rp->free_instances.first,
struct kretprobe_instance, hlist);
@@ -1953,7 +1970,7 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
ri->task = current;
if (rp->entry_handler && rp->entry_handler(ri, regs)) {
- raw_spin_lock_irqsave(&rp->lock, flags);
+ raw_spin_lock_irqsave_nested(&rp->lock, flags, 1);
hlist_add_head(&ri->hlist, &rp->free_instances);
raw_spin_unlock_irqrestore(&rp->lock, flags);
return 0;
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH 1/2] kprobes: Remove NMI context check
2020-12-10 15:30 [PATCH 1/2] kprobes: Remove NMI context check Masami Hiramatsu
2020-12-10 15:31 ` [PATCH 2/2] kprobes: Tell lockdep about kprobe nesting Masami Hiramatsu
@ 2020-12-11 14:47 ` Greg KH
1 sibling, 0 replies; 3+ messages in thread
From: Greg KH @ 2020-12-11 14:47 UTC (permalink / raw)
To: Masami Hiramatsu
Cc: stable, Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H . Peter Anvin, linux-kernel, Naveen N . Rao,
Anil S Keshavamurthy, David S . Miller, Solar Designer, Eddy_Wu,
Peter Zijlstra
On Fri, Dec 11, 2020 at 12:30:58AM +0900, Masami Hiramatsu wrote:
> commit e03b4a084ea6b0a18b0e874baec439e69090c168 upstream.
Both patches now queued up, thanks.
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-12-11 15:17 UTC | newest]
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2020-12-10 15:30 [PATCH 1/2] kprobes: Remove NMI context check Masami Hiramatsu
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2020-12-11 14:47 ` [PATCH 1/2] kprobes: Remove NMI context check Greg KH
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