linux-kernel - Re: [PATCH 1/2] x86/Xen/32: make xen_iret_crit

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Date:   Tue, 19 Nov 2019 14:17:42 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH 1/2] x86/Xen/32: make xen_iret_crit_fixup independent of
 frame layout

On 11.11.19 15:32, Jan Beulich wrote:
> Now that SS:ESP always get saved by SAVE_ALL, this also needs to be
> accounted for in xen_iret_crit_fixup. Otherwise the old_ax value gets
> interpreted as EFLAGS, and hence VM86 mode appears to be active all
> the time, leading to random "vm86_32: no user_vm86: BAD" log messages
> alongside processes randomly crashing.
> 
> Since following the previous model (sitting after SAVE_ALL) would
> further complicate the code _and_ retain the dependency of
> xen_iret_crit_fixup on frame manipulations done by entry_32.S, switch
> things around and do the adjustment ahead of SAVE_ALL.
> 
> Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs")
> Signed-off-by: Jan Beulich <jbeulich@...e.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen