From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
"Andy Lutomirski" <luto@kernel.org>
Subject: Re: [PATCH 2/3] x86/pv: Don't clobber NT on return-to-guest
Date: Thu, 24 Sep 2020 15:57:06 +0200 [thread overview]
Message-ID: <339f0abd-65ad-7be0-a3f0-149fcac9a0a3@suse.com> (raw)
In-Reply-To: <20200923101848.29049-3-andrew.cooper3@citrix.com>
On 23.09.2020 12:18, Andrew Cooper wrote:
> A 64bit IRET can restore NT - the faulting case is when NT is set in the live
> flags. This change had an unintended consequence of causing the NT flag to
> spontaneously disappear from guest context whenever a interrupt/exception
> occurred.
>
> In combination with a SYSENTER which sets both TF and NT, Xen's handling of
> the #DB exceptions clears NT before it is even recorded suitably in the guest
> kernel's view of what userspace was doing.
>
> Reported-by: Andy Lutomirski <luto@kernel.org>
> Fixes: 0e47f92b0 ("x86: force EFLAGS.IF on when exiting to PV guests")
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
next prev parent reply other threads:[~2020-09-24 13:57 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 10:18 [PATCH 0/3] x86/pv: Multiple fixes to SYSCALL/SYSENTER handling (XSA-339 followup) Andrew Cooper
2020-09-23 10:18 ` [PATCH 1/3] x86/pv: Don't deliver #GP for a SYSENTER with NT set Andrew Cooper
2020-09-24 13:55 ` Jan Beulich
2020-09-23 10:18 ` [PATCH 2/3] x86/pv: Don't clobber NT on return-to-guest Andrew Cooper
2020-09-24 13:57 ` Jan Beulich [this message]
2020-09-23 10:18 ` [PATCH 3/3] x86/pv: Inject #UD for missing SYSCALL callbacks Andrew Cooper
2020-09-24 14:56 ` Jan Beulich
2020-09-28 13:05 ` Andrew Cooper
2020-09-28 15:35 ` Jan Beulich
2020-10-09 11:53 ` [PATCH v2] " Andrew Cooper
2020-10-09 12:40 ` Manuel Bouyer
2020-10-09 12:50 ` Andrew Cooper
2020-10-14 14:16 ` Roger Pau Monné
2020-10-14 14:20 ` Manuel Bouyer
2020-10-14 14:26 ` Andrew Cooper
2020-10-14 15:17 ` Andrew Cooper
2020-10-14 16:28 ` Roger Pau Monné
2020-10-14 17:41 ` Andrew Cooper
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