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From: Mark Rutland <mark.rutland@arm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>, Will Deacon <will@kernel.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Waiman Long <longman@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH] x86/uaccess: Use pointer masking to limit uaccess speculation
Date: Fri, 4 Sep 2020 17:00:06 +0100	[thread overview]
Message-ID: <20200904160006.GA21956@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20200903065613.GA18731@lst.de>

On Thu, Sep 03, 2020 at 08:56:13AM +0200, Christoph Hellwig wrote:
> On Wed, Sep 02, 2020 at 06:23:30PM +0100, Mark Rutland wrote:
> > I've pushed an initial/incomplete/WIP stab (just the kernel accessors)
> > to:
> > 
> > https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/set_fs-removal
> 
> Thanks!
> 
> > ... and doing that made it clear that the necessary arm64 rework is a
> > bit more fractal than I thought (e.g. SDEI bits), so it might be a short
> > while before I post a series.
> 
> SDEI is just forcing back a KERNEL_DS to a normal USER_DS, isn't it?
 
It's a bit more involved -- we also need to fiddle with some HW state
(PSTATE.PAN, PSTATE.UAO, and TTBR0 for SW_PAN) because SDEI isn't a real
exception, so we have to simulate what HW (or the usual exception code)
does for exception entry/return.

It's simple enough to handle, but requires some refactoring as we now
rely on force_uaccess_{begin,end}() having those HW side-effects. I'll
probably factor that out into new arm64-specific helpers for simulating
exception entry/return (which we used to open-code) since it's the only
special case and that'll be clearer than repurposing generic helpers to
do so.

> > It might be handy to have a stable branch with the common bits so that
> > the arm64 rework could go via the arm64 tree in case there's any
> > fallout.
> 
> The series will need at least one more repost, but hopefully I'll have
> s stable branch soon.

I'll keep an eye out!

Mark.

      reply	other threads:[~2020-09-04 16:00 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19 14:50 [PATCH] x86/uaccess: Use pointer masking to limit uaccess speculation Josh Poimboeuf
2020-08-19 16:39 ` Andy Lutomirski
2020-08-19 17:02   ` Josh Poimboeuf
2020-08-19 21:30     ` David Laight
2020-08-20  0:18     ` Andy Lutomirski
2020-08-28 19:29 ` Josh Poimboeuf
2020-08-29 13:21   ` David Laight
2020-08-29 19:31     ` David Laight
2020-08-31 17:31       ` Josh Poimboeuf
2020-09-01  8:32         ` David Laight
2020-09-01 14:26           ` Josh Poimboeuf
2020-09-01 15:00             ` David Laight
2020-09-01 15:24               ` Josh Poimboeuf
2020-09-01 14:02 ` Mark Rutland
2020-09-01 14:21   ` Josh Poimboeuf
2020-09-01 14:52     ` Mark Rutland
2020-09-01 14:46   ` Christoph Hellwig
2020-09-01 14:54     ` Mark Rutland
2020-09-01 15:05       ` Christoph Hellwig
2020-09-01 15:46         ` Christoph Hellwig
2020-09-02 11:43           ` Mark Rutland
2020-09-02 13:32             ` Christoph Hellwig
2020-09-02 17:23               ` Mark Rutland
2020-09-03  6:56                 ` Christoph Hellwig
2020-09-04 16:00                   ` Mark Rutland [this message]

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