linux-kernel - Re: [PATCH 1/3] x86, ras: Add new infrastructure for machine check fixup tables

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Date:	Thu, 12 Nov 2015 13:17:41 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-edac <linux-edac@...r.kernel.org>, X86 ML <x86@...nel.org>,
	DanWilliamsdan.j.williams@...el.com
Subject: Re: [PATCH 1/3] x86, ras: Add new infrastructure for machine check
 fixup tables

On Thu, Nov 12, 2015 at 12:04:36PM -0800, Andy Lutomirski wrote:
> > We already have code to recover from machine checks encountered
> > while the processor is executing ring3 code.
> 
> I meant failures during copy_from_user, copy_to_user, etc.

Yes.  copy_from_user() will be pretty interesting from a coverage point
of view.  We can recover by sending a SIGBUS to the process just like
we would have if the process had accessed the data directly rather than
passing the address to the kernel to acccess it.

copy_to_user() is a lot harder. The machine check is on the kernel side
of the copy. If we are copying from page cache as part of a read(2)
syscall from a regular file we can probably nuke the page from the cache
and return -EIO to the user.  Other cases may be possible, but I don't
immediately see any way to do it as a general case.

-Tony
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