linux-kernel - Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine

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Date:   Wed, 26 Feb 2020 12:18:27 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [patch 02/10] x86/mce: Disable tracing and kprobes on
 do_machine_check()

On Tue, Feb 25, 2020 at 10:36:38PM +0100, Thomas Gleixner wrote:
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -1213,8 +1213,14 @@ static void __mc_scan_banks(struct mce *
>   * On Intel systems this is entered on all CPUs in parallel through
>   * MCE broadcast. However some CPUs might be broken beyond repair,
>   * so be always careful when synchronizing with others.
> + *
> + * Tracing and kprobes are disabled: if we interrupted a kernel context
> + * with IF=1, we need to minimize stack usage.  There are also recursion
> + * issues: if the machine check was due to a failure of the memory
> + * backing the user stack, tracing that reads the user stack will cause
			      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Had to read this a couple of times to parse that formulation properly.
Make that

"... backing the user stack, tracing code which accesses same user stack
will potentially cause an infinite recursion."

With that:

Reviewed-by: Borislav Petkov <bp@...e.de>

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette