Re: [PATCH] misc: enable retpolines across all xfsprogs utilities

[Matthias Schniedermeyer <ms@citd.de>]

On 22.02.2018 09:15, Darrick J. Wong wrote:
> On Thu, Feb 22, 2018 at 09:31:41AM -0600, Eric Sandeen wrote:
> > On 2/22/18 9:09 AM, Christoph Hellwig wrote:
> > > On Wed, Feb 21, 2018 at 06:16:25PM -0800, Darrick J. Wong wrote:
> > >> From: Darrick J. Wong <darrick.wong@oracle.com>
> > >>
> > >> Detect and enable retpolines for all code, to mitigate Spectre v2
> > >> (branch target injection) on x86.
> > > 
> > > The mechanics look ok, but why do we really care for xfsprogs?
> > > fs utilities seem like a lesser target and should just be covered
> 
> They're a smaller target than the kernel, for sure, but the scary part
> about spectre is that unprivileged programs running on the same core as
> a privileged xfs_repair can then use branch predictor poisoning to cause
> problems with the xfs_repair.

Spectre & Meltdown are information disclosure vulnerabilities IOW "Read 
Only".
The other process CAN NOT interfere with xfs_repair.

I would speculate that the most it can get, is information about parts 
of the filesystem that are inaccsessible to an unprivileged process by 
spying on xfs_repair.
I don't know how xfs_repair works, especially how xfs_repair handles 
storing data in memory. But for xfs_repair to be a good target, it 
would have to store relevant data in a deterministic fashion and for 
some length of time. At least enough to justify writing an extraction 
program for it.

I would say the 'good old' xfs_repair case isn't really a good target, 
but the online-scrubbing-case sure sounds to be a different beast.

In the past you couldn't, for a given point in time, really expect a 
xfs_repair process to be running, but with online-scrubbing that game 
changes.





-- 

Matthias