Messages in this thread | | | From | Masami Hiramatsu <> | Subject | [BUGFIX PATCH tip/master 0/3] kprobes: Fix a possible deadlock in kretprobe | Date | Wed, 8 Feb 2017 00:10:52 +0900 |
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Hi,
This series will fix a possible deadlock case in kretprobe on x86, arm, arm64. Since kretprobe has been optimized on those arch, they have similar possible deadlock issue.
Problem =====
The deadlock senario is when a user puts 2 kretprobes, one on normal function and one on a function which can be called from NMI or FIQ where normal interrupt disabled. (we don't recommend it, but possible.) In this case, if the kernel hits the 1st kretprobe on a normal function return which calls trampoline_handler(), acquire a spinlock on the hash table in kretprobe_hash_lock() and disable irqs. After that, if NMI(or FIQ on arm/arm64) is occurred and the 2nd kretprobe is kicked, it also calls trampoline_handler() and tries to acquire the same spinlock (since the hash is based on current task, same as the 1st kretprobe), it causes a deadlock on the spinlock. Note that this is very rare case, but theoretically happens.
Reason and Affected Arch =====
Actually, this bug has been introduced by kretprobe-booster, which removes a kprobe from return trampoline code, but also resets current kprobe, which can be a stopper for the nested k(ret)probes. So, currently only x86, arm, and arm64 are affected, because other arch have not implemented the kretprobe-booster.
Solution =====
To fix this issue, I introduced a dummy kprobe which is set as a current kprobe while holding the kretprobe-hash lock. With that, if an NMI/FIQ occurred and 2nd kretprobe's kprobe is kicked (to modify the return address, a kprobe is kicked when the target function is called), the kprobe (and the 2nd kretprobe also) is skipped because it detects there is another kprobe is running. This reentrance detection and nested kprobe blocker had existed when the original kretprobe was implemented by using kprobe on trampoline code. This fix just revived it.
Thank you,
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Masami Hiramatsu (3): kprobes/x86: Fix a possible deadlock case in kretprobe kprobes/arm64: Fix a possible deadlock case in kretprobe kprobes/arm: Fix a possible deadlock case in kretprobe
arch/arm/probes/kprobes/core.c | 12 ++++++++++-- arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++-- arch/x86/kernel/kprobes/core.c | 13 ++++++++++--- 3 files changed, 30 insertions(+), 7 deletions(-)
-- Masami Hiramatsu
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