linux-kernel - Re: [PATCH v3 19/30] liveupdate: luo

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Message-ID: <CA+CK2bBz3NvDmwUjCPiyTPH9yL6YpZ+vX=o2TkC2C7aViXO-pQ@mail.gmail.com>
Date: Thu, 9 Oct 2025 13:04:57 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
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Subject: Re: [PATCH v3 19/30] liveupdate: luo_sysfs: add sysfs state monitoring

On Thu, Oct 9, 2025 at 11:35 AM Zhu Yanjun <yanjun.zhu@...ux.dev> wrote:
>
>
> 在 2025/10/9 5:01, Pasha Tatashin 写道:
> >>> Because the window of kernel live update is short, it is difficult to statistics
> >>> how many times the kernel is live updated.
> >>>
> >>> Is it possible to add a variable to statistics the times that the kernel is live
> >>> updated?
> >> The kernel doesn't do the live update on its own. The process is driven
> >> and sequenced by userspace. So if you want to keep statistics, you
> >> should do it from your userspace (luod maybe?). I don't see any need for
> >> this in the kernel.
> >>
> > One use case I can think of is including information in kdump or the
> > backtrace warning/panic messages about how many times this machine has
> > been live-updated. In the past, I've seen bugs (related to memory
> > corruption) that occurred only after several kexecs, not on the first
> > one. With live updates, especially while the code is being stabilized,
> > I imagine we might have a similar situation. For that reason, it could
> > be useful to have a count in the dmesg logs showing how many times
> > this machine has been live-updated. While this information is also
> > available in userspace, it would be simpler for kernel developers
> > triaging these issues if everything were in one place.
> I’m considering this issue from a system security perspective. After the
> kernel is automatically updated, user-space applications are usually
> unaware of the change. In one possible scenario, an attacker could
> replace the kernel with a compromised version, while user-space
> applications remain unaware of it — which poses a potential security risk.
>
> To mitigate this, it would be useful to expose the number of kernel
> updates through a sysfs interface, so that we can detect whether the
> kernel has been updated and then collect information about the new
> kernel to check for possible security issues.
>
> Of course, there are other ways to detect kernel updates — for example,
> by using ftrace to monitor functions involved in live kernel updates —
> but such approaches tend to have a higher performance overhead. In
> contrast, adding a simple update counter to track live kernel updates
> would provide similar monitoring capability with minimal overhead.

Would a print during boot, i.e. when we print that this kernel is live
updating, we could include the number, work for you? Otherwise, we
could export this number in a debugfs.

Pasha