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From: Mark Rutland <mark.rutland@arm.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: 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>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] x86/uaccess: Use pointer masking to limit uaccess speculation
Date: Tue, 1 Sep 2020 15:52:03 +0100	[thread overview]
Message-ID: <20200901145203.GB95447@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20200901142158.fo7tecobgki5hffa@treble>

On Tue, Sep 01, 2020 at 09:21:58AM -0500, Josh Poimboeuf wrote:
> On Tue, Sep 01, 2020 at 03:02:08PM +0100, Mark Rutland wrote:
> > d instead do user pointer
> > > masking, throughout the x86 uaccess code.  This is similar to what arm64
> > > is already doing.
> > > 
> > > barrier_nospec() is now unused, and can be removed.
> > 
> > One thing to consider is whether you need a speculation barrier after
> > set_fs(). Otherwise for code like:
> > 
> > | fs = get_fs();
> > | if (cond)
> > |	set_fs(KERNEL_DS);
> > | copy_to_user(...)
> > | set_fs(fs)
> > 
> > ... the set_fs() can occur speculatively, and may be able to satisfy
> > the masking logic if forwarded within the cpu.
> > 
> > See arm64 commit:
> > 
> >   c2f0ad4fc089cff8 ("arm64: uaccess: Prevent speculative use of the current addr_limit")
> 
> Do you have any examples of that conditional set_fs(KERNEL_DS) pattern?
> I wasn't able to find any.

I'm afraid not -- we used to in arm64 in some memory dump code, but that
is now gone. It might be that this is no longer necessary.

If set_fs() goes entirely, that's even better...

Thanks,
Mark.

  reply	other threads:[~2020-09-01 14:52 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 [this message]
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

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