From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
Tim Deegan <tim@xen.org>,
George Dunlap <george.dunlap@citrix.com>
Subject: Re: [PATCH 02/17] x86: split __{get,put}_user() into "guest" and "unsafe" variants
Date: Fri, 5 Feb 2021 17:18:51 +0100 [thread overview]
Message-ID: <YB1v60CuOdhxFwNy@Air-de-Roger> (raw)
In-Reply-To: <d23dc40c-3b37-ade2-f987-4f79b06901b1@suse.com>
On Fri, Feb 05, 2021 at 05:13:22PM +0100, Jan Beulich wrote:
> On 05.02.2021 16:43, Roger Pau Monné wrote:
> > On Thu, Jan 14, 2021 at 04:04:11PM +0100, Jan Beulich wrote:
> >> The "guest" variants are intended to work with (potentially) fully guest
> >> controlled addresses, while the "unsafe" variants are not.
> >
> > Just to clarify, both work against user addresses, but guest variants
> > need to be more careful because the guest provided address can also be
> > modified?
> >
> > I'm trying to understand the difference between "fully guest
> > controlled" and "guest controlled".
>
> Not exactly, not. "unsafe" means access to anything which may
> fault, guest controlled or not. do_invalid_op()'s reading of
> the insn stream is a good example - the faulting insn there
> isn't guest controlled at all, but we still want to be careful
> when trying to read these bytes, as we don't want to fully
> trust %rip there.
Would it make sense to threat everything as 'guest' accesses for the
sake of not having this difference?
I think having two accessors it's likely to cause confusion and could
possibly lead to the wrong one being used in unexpected contexts. Does
it add a too big performance penalty to always use the most
restrictive one?
Thanks, Roger.
next prev parent reply other threads:[~2021-02-05 16:19 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-14 15:01 [PATCH 00/17] x86/PV: avoid speculation abuse through guest accessors plus Jan Beulich
2021-01-14 15:03 ` [PATCH 01/17] x86/shadow: use __put_user() instead of __copy_to_user() Jan Beulich
2021-01-14 15:04 ` [PATCH 02/17] x86: split __{get,put}_user() into "guest" and "unsafe" variants Jan Beulich
2021-02-05 15:43 ` Roger Pau Monné
2021-02-05 16:13 ` Jan Beulich
2021-02-05 16:18 ` Roger Pau Monné [this message]
2021-02-05 16:26 ` Jan Beulich
2021-02-09 13:07 ` Roger Pau Monné
2021-02-09 13:15 ` Jan Beulich
2021-02-09 14:46 ` Roger Pau Monné
2021-02-09 14:57 ` Jan Beulich
2021-02-09 15:23 ` Roger Pau Monné
2021-02-09 14:55 ` Roger Pau Monné
2021-02-09 15:14 ` Jan Beulich
2021-02-09 15:27 ` Roger Pau Monné
2021-01-14 15:04 ` [PATCH 03/17] x86: split __copy_{from,to}_user() " Jan Beulich
2021-02-09 16:06 ` Roger Pau Monné
2021-02-09 17:03 ` Jan Beulich
2021-01-14 15:04 ` [PATCH 04/17] x86/PV: harden guest memory accesses against speculative abuse Jan Beulich
2021-02-09 16:26 ` Roger Pau Monné
2021-02-10 16:55 ` Jan Beulich
2021-02-11 8:11 ` Roger Pau Monné
2021-02-11 11:28 ` Jan Beulich
2021-02-12 10:41 ` Roger Pau Monné
2021-02-12 12:48 ` Jan Beulich
2021-02-12 13:02 ` Roger Pau Monné
2021-02-12 13:15 ` Jan Beulich
2021-01-14 15:05 ` [PATCH 05/17] x86: rename {get,put}_user() to {get,put}_guest() Jan Beulich
2021-01-14 15:05 ` [PATCH 06/17] x86/gdbsx: convert "user" to "guest" accesses Jan Beulich
2021-01-14 15:06 ` [PATCH 07/17] x86: rename copy_{from,to}_user() to copy_{from,to}_guest_pv() Jan Beulich
2021-01-14 15:07 ` [PATCH 08/17] x86: move stac()/clac() from {get,put}_unsafe_asm() Jan Beulich
2021-01-14 15:07 ` [PATCH 09/17] x86/PV: use get_unsafe() instead of copy_from_unsafe() Jan Beulich
2021-01-14 15:08 ` [PATCH 10/17] x86/shadow: " Jan Beulich
2021-01-14 15:08 ` [PATCH 11/17] x86/shadow: polish shadow_write_entries() Jan Beulich
2021-01-14 15:09 ` [PATCH 12/17] x86/shadow: move shadow_set_l<N>e() to their own source file Jan Beulich
2021-01-14 15:09 ` [PATCH 13/17] x86/shadow: don't open-code SHF_* shorthands Jan Beulich
2021-01-14 15:10 ` [PATCH 14/17] x86/shadow: SH_type_l2h_shadow is PV-only Jan Beulich
2021-01-14 15:10 ` [PATCH 15/17] x86/shadow: drop SH_type_l2h_pae_shadow Jan Beulich
2021-01-22 13:11 ` Tim Deegan
2021-01-22 16:31 ` Jan Beulich
2021-01-22 20:02 ` Tim Deegan
2021-01-25 11:09 ` Jan Beulich
2021-01-25 11:33 ` Jan Beulich
2021-01-14 15:10 ` [PATCH 16/17] x86/shadow: only 4-level guest code needs building when !HVM Jan Beulich
2021-01-14 15:11 ` [PATCH 17/17] x86/shadow: adjust is_pv_*() checks Jan Beulich
2021-01-22 13:18 ` [PATCH 00/17] x86/PV: avoid speculation abuse through guest accessors plus Tim Deegan
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