Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 17 Jan 2018 20:05:32 +0000
From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Alan Cox <alan@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        kernel-hardening@lists.openwall.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in
 get_user paths
Message-ID: <20180117200532.GX13338@ZenIV.linux.org.uk>
References: <151586744180.5820.13215059696964205856.stgit@dwillia2-desk3.amr.corp.intel.com>
 <151586748981.5820.14559543798744763404.stgit@dwillia2-desk3.amr.corp.intel.com>
 <CA+55aFzoAR+MYX+ub0xZ32OsT7WtD5Kru2t6LhwB1buLWPResQ@mail.gmail.com>
 <CA+55aFxsg5+u7bCHj1N8xyyVf7-RMm-5ACNp=ENNrKL78omaow@mail.gmail.com>
 <CAPcyv4hfUx8gLScuNewY3+BWi4YBS_Z9dhvYf1D+WEWDDCShXA@mail.gmail.com>
 <CA+55aFxAFG5czVmCyhYMyHmXLNJ7pcXxWzusjZvLRh_qTGHj6Q@mail.gmail.com>
 <CA+55aFxB01XEEpdPynwYmzQMfTJdJnUrN+ZLqSV_UdnKLBgAZw@mail.gmail.com>
 <1516198646.4184.13.camel@linux.intel.com>
 <20180117185232.GW13338@ZenIV.linux.org.uk>
 <CAPcyv4iYVcCZxdd5wHDf2av8F=E1F7UGTX9uVzX68KkrJ1ZuQQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAPcyv4iYVcCZxdd5wHDf2av8F=E1F7UGTX9uVzX68KkrJ1ZuQQ@mail.gmail.com>
User-Agent: Mutt/1.9.1 (2017-09-22)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jan 17, 2018 at 11:54:12AM -0800, Dan Williams wrote:
> On Wed, Jan 17, 2018 at 10:52 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > On Wed, Jan 17, 2018 at 02:17:26PM +0000, Alan Cox wrote:
> [..]
> >         Incidentally, what about copy_to_iter() and friends?  They
> > check iov_iter flavour and go either into the "copy to kernel buffer"
> > or "copy to userland" paths.  Do we need to deal with mispredictions
> > there?  We are calling a bunch of those on read()...
> >
> 
> Those should be protected by the conversion of __uaccess_begin to
> __uaccess_begin_nospec that includes the lfence.

Huh?  What the hell does it do to speculative execution of "memcpy those
suckers" branch?