From: Brian Gerst <brgerst@gmail.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH] x86: Remove force_iret()
Date: Thu, 19 Dec 2019 22:48:13 -0500 [thread overview]
Message-ID: <CAMzpN2if2m4McWpL49U4QAEM1MJ+qgTe-emN8vKcjVc1H+84vA@mail.gmail.com> (raw)
In-Reply-To: <CALCETrW1zE0Uufrg_UG4JNQKMy3UFxnd+XmZye2gdTV36C-yTw@mail.gmail.com>
On Thu, Dec 19, 2019 at 8:50 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Thu, Dec 19, 2019 at 3:58 AM Brian Gerst <brgerst@gmail.com> wrote:
> >
> > force_iret() was originally intended to prevent the return to user mode with
> > the SYSRET or SYSEXIT instructions, in cases where the register state could
> > have been changed to be incompatible with those instructions.
>
> It's more than that. Before the big syscall rework, we didn't restore
> the caller-saved regs. See:
>
> commit 21d375b6b34ff511a507de27bf316b3dde6938d9
> Author: Andy Lutomirski <luto@kernel.org>
> Date: Sun Jan 28 10:38:49 2018 -0800
>
> x86/entry/64: Remove the SYSCALL64 fast path
>
> So if you changed r12, for example, the change would get lost.
force_iret() specifically dealt with changes to CS, SS and EFLAGS.
Saving and restoring the extra registers was a different problem
although it affected the same functions like ptrace, signals, and
exec.
--
Brian Gerst
next prev parent reply other threads:[~2019-12-20 3:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-19 11:58 [PATCH] x86: Remove force_iret() Brian Gerst
2019-12-20 1:49 ` Andy Lutomirski
2019-12-20 3:48 ` Brian Gerst [this message]
2019-12-20 10:10 ` David Laight
2019-12-20 10:30 ` Andy Lutomirski
2019-12-20 10:59 ` David Laight
2019-12-20 21:20 ` Andy Lutomirski
2019-12-20 12:18 ` Brian Gerst
2019-12-20 12:35 ` David Laight
2019-12-20 19:35 ` Oleg Nesterov
2020-01-08 20:30 ` [tip: x86/asm] " tip-bot2 for Brian Gerst
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