From: Josh Poimboeuf <jpoimboe@redhat.com>
To: David Laight <David.Laight@aculab.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.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>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH v2] x86/uaccess: Use pointer masking to limit uaccess speculation
Date: Wed, 9 Sep 2020 07:46:44 -0500 [thread overview]
Message-ID: <20200909124644.dndmfnoob5qzd7xi@treble> (raw)
In-Reply-To: <01b027d0d46d4572b3b16e2b49f0f2b3@AcuMS.aculab.com>
On Wed, Sep 09, 2020 at 08:20:07AM +0000, David Laight wrote:
> From: Josh Poimboeuf <jpoimboe@redhat.com>
> > Sent: 08 September 2020 18:43
> > Hi x86 maintainers,
> ...
> > > --- a/arch/x86/lib/putuser.S
> > > +++ b/arch/x86/lib/putuser.S
> > > @@ -38,6 +38,8 @@ SYM_FUNC_START(__put_user_1)
> > > ENTER
> > > cmp TASK_addr_limit(%_ASM_BX),%_ASM_CX
> > > jae .Lbad_put_user
> > > + sbb %_ASM_BX, %_ASM_BX /* uaccess_mask_ptr() */
> > > + and %_ASM_BX, %_ASM_CX
> > > ASM_STAC
> > > 1: movb %al,(%_ASM_CX)
> > > xor %eax,%eax
>
> For 64bit the sbb+and pattern can be replaced by an instruction
> that clears the high bit (eg btr $63, %rcx).
> This isn't dependant on the earlier instructions so can execute
> in parallel with them.
Wouldn't that break with KERNEL_DS?
> I still think that doing the same comparisons in access_ok()
> and for the pointer masking is silly - and they should get merged.
I agree, but as I said multiple times already, that will be a much
bigger change (tree-wide and multi-arch) which comes later.
--
Josh
next prev parent reply other threads:[~2020-09-09 14:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-01 15:30 Josh Poimboeuf
2020-09-08 17:43 ` Josh Poimboeuf
2020-09-09 8:20 ` David Laight
2020-09-09 12:46 ` Josh Poimboeuf [this message]
2020-09-09 13:00 ` Josh Poimboeuf
2020-09-09 13:46 ` David Laight
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