linux-kernel - Re: [PATCH v2 1/1] arch/fault: don't print logs for pte marker poison errors

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Message-ID: <20240515183222.GCZkT_tvEffgYtah4T@fat_crate.local>
Date: Wed, 15 May 2024 20:32:22 +0200
From: Borislav Petkov <bp@...en8.de>
To: Axel Rasmussen <axelrasmussen@...gle.com>
Cc: Oscar Salvador <osalvador@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Helge Deller <deller@....de>,
	Ingo Molnar <mingo@...hat.com>,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	John Hubbard <jhubbard@...dia.com>,
	Liu Shixin <liushixin2@...wei.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Muchun Song <muchun.song@...ux.dev>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>, Peter Xu <peterx@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v2 1/1] arch/fault: don't print logs for pte marker
 poison errors

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