linux-hardening - Re: [PATCH] Revert "ACPI, APEI, use raw spinlock in ERST"

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Message-ID: <ZOQodU1CNMRtjYZ6@cork>
Date:   Mon, 21 Aug 2023 20:16:05 -0700
From:   Jörn Engel <joern@...estorage.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Uday Shankar <ushankar@...estorage.com>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, James Morse <james.morse@....com>,
        Borislav Petkov <bp@...en8.de>,
        Len Brown <len.brown@...el.com>,
        linux-hardening@...r.kernel.org, linux-acpi@...r.kernel.org,
        Qiuxu Zhuo <qiuxu.zhuo@...el.com>
Subject: Re: [PATCH] Revert "ACPI, APEI, use raw spinlock in ERST"

On Tue, Aug 22, 2023 at 09:56:38AM +0800, Huang, Ying wrote:
> 
> ERST is mainly used to log the hardware error.  While, hardware error
> may be reported via NMI (e.g., ACPI APEI GHES NMI), so we need to call
> ERST functions in NMI handlers.  Where normal spinlock cannot be used
> because they will be converted to sleepable rt_mutex in RT kernel.

Non-sleeping spinlocks cannot be used in NMI context either.
raw_spin_lock_irqsave() will prevent regular interrupts, but not NMI.
So taking a spinlock inside an NMI can trigger a deadlock.

Am I missing something here?

Jörn

--
All art is but imitation of nature.
-- Lucius Annaeus Seneca