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Date: Wed, 15 May 2024 20:32:22 +0200
From: Borislav Petkov <bp@alien8.de>
To: Axel Rasmussen <axelrasmussen@google.com>
Cc: Oscar Salvador <osalvador@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
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	"H. Peter Anvin" <hpa@zytor.com>, Helge Deller <deller@gmx.de>,
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	Muchun Song <muchun.song@linux.dev>,
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Subject: Re: [PATCH v2 1/1] arch/fault: don't print logs for pte marker
 poison errors
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On Wed, May 15, 2024 at 10:33:03AM -0700, Axel Rasmussen wrote:
> Right, the goal is to still have the process get a SIGBUS, but to
> avoid the "MCE error" log message. The basic issue is, unprivileged
> users can set these markers up, and thereby completely spam up the
> log.

What is the real attack scenario you want to protect against?

Or is this something hypothetical?

> That said, one thing I'm not sure about is whether or not
> VM_FAULT_SIGBUS is a viable alternative (returned for a new PTE marker
> type specific to simulated poison). The goal of the simulated poison
> feature is to "closely simulate" a real hardware poison event. If you
> live migrate a VM from a host with real poisoned memory, to a new
> host: you'd want to keep the same behavior if the guest accessed those
> addresses again, so as not to confuse the guest about why it suddenly
> became "un-poisoned".

Well, the recovery action is to poison the page and the process should
be resilient enough and allocate a new, clean page which doesn't trigger
hw poison hopefully, if possible.

It doesn't make a whole lotta sense if poison "remains". Hardware poison
you don't want to touch a second time either - otherwise you might
consume that poison and die.

-- 
Regards/Gruss,
    Boris.

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