From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Mark Rutland <mark.rutland@arm.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 09:21:58 -0500 [thread overview]
Message-ID: <20200901142158.fo7tecobgki5hffa@treble> (raw)
In-Reply-To: <20200901140208.GA95447@C02TD0UTHF1T.local>
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.
--
Josh
next prev parent reply other threads:[~2020-09-01 14:24 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 [this message]
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
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