linux-kernel - Re: [PATCH V4 1/7] x86/traps: Move pt_regs only in fixup_bad

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Message-ID: <CAJhGHyByXaeaYqq54EY6YoNwf4DrupCXeZmtdi9ViYwmDx2ffQ@mail.gmail.com>
Date:   Fri, 8 Apr 2022 09:56:26 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Tai <thomas.tai@...cle.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH V4 1/7] x86/traps: Move pt_regs only in fixup_bad_iret()

On Thu, Apr 7, 2022 at 9:19 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Apr 07, 2022 at 10:22:25AM +0200, Borislav Petkov wrote:
> > Maybe there was a reason it was done this way:
>
> Ok, I went and singlestepped this code so that I can see what's going
> on.

[....]

>
> So your commit message should have been as simple as:
>
> "Always stash the address error_entry() is going to return to, in %r12
> and get rid of the void *error_entry_ret; slot in struct bad_iret_stack
> which was supposed to account for it and pt_regs pushed on the stack.
>
> After this, both functions can work on a struct pt_regs pointer
> directly."

Thank you for elaborating on the details and I will use this changelog.

Thanks
Lai

>
> In any case, I don't see why amluto would do this so this looks like a
> sensible cleanup to do.
>