6.1-stable review patch. If anyone has any objections, please let me know.
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From: Andrey Konovalov andreyknvl@gmail.com
commit 7d4df2dad312f270d62fecb0e5c8b086c6d7dcfc upstream.
When collecting coverage from softirqs, KCOV uses in_serving_softirq() to check whether the code is running in the softirq context. Unfortunately, in_serving_softirq() is > 0 even when the code is running in the hardirq or NMI context for hardirqs and NMIs that happened during a softirq.
As a result, if a softirq handler contains a remote coverage collection section and a hardirq with another remote coverage collection section happens during handling the softirq, KCOV incorrectly detects a nested softirq coverate collection section and prints a WARNING, as reported by syzbot.
This issue was exposed by commit a7f3813e589f ("usb: gadget: dummy_hcd: Switch to hrtimer transfer scheduler"), which switched dummy_hcd to using hrtimer and made the timer's callback be executed in the hardirq context.
Change the related checks in KCOV to account for this behavior of in_serving_softirq() and make KCOV ignore remote coverage collection sections in the hardirq and NMI contexts.
This prevents the WARNING printed by syzbot but does not fix the inability of KCOV to collect coverage from the __usb_hcd_giveback_urb when dummy_hcd is in use (caused by a7f3813e589f); a separate patch is required for that.
Link: https://lkml.kernel.org/r/20240729022158.92059-1-andrey.konovalov@linux.dev Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts") Signed-off-by: Andrey Konovalov andreyknvl@gmail.com Reported-by: syzbot+2388cdaeb6b10f0c13ac@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2388cdaeb6b10f0c13ac Acked-by: Marco Elver elver@google.com Cc: Alan Stern stern@rowland.harvard.edu Cc: Aleksandr Nogikh nogikh@google.com Cc: Alexander Potapenko glider@google.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Marcello Sylvester Bauer sylv@sylv.io Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/kcov.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
--- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -161,6 +161,15 @@ static void kcov_remote_area_put(struct kmsan_unpoison_memory(&area->list, sizeof(area->list)); }
+/* + * Unlike in_serving_softirq(), this function returns false when called during + * a hardirq or an NMI that happened in the softirq context. + */ +static inline bool in_softirq_really(void) +{ + return in_serving_softirq() && !in_hardirq() && !in_nmi(); +} + static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t) { unsigned int mode; @@ -170,7 +179,7 @@ static notrace bool check_kcov_mode(enum * so we ignore code executed in interrupts, unless we are in a remote * coverage collection section in a softirq. */ - if (!in_task() && !(in_serving_softirq() && t->kcov_softirq)) + if (!in_task() && !(in_softirq_really() && t->kcov_softirq)) return false; mode = READ_ONCE(t->kcov_mode); /* @@ -847,7 +856,7 @@ void kcov_remote_start(u64 handle)
if (WARN_ON(!kcov_check_handle(handle, true, true, true))) return; - if (!in_task() && !in_serving_softirq()) + if (!in_task() && !in_softirq_really()) return;
local_lock_irqsave(&kcov_percpu_data.lock, flags); @@ -989,7 +998,7 @@ void kcov_remote_stop(void) int sequence; unsigned long flags;
- if (!in_task() && !in_serving_softirq()) + if (!in_task() && !in_softirq_really()) return;
local_lock_irqsave(&kcov_percpu_data.lock, flags);