linux-kernel - Re: [PATCH] x86/sev: Add ENCODE_FRAME_POINTER after stack changed for #VC

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Message-ID: <CAJhGHyC1qPee2QOpgR8B+2Sd+XzfoJD3NL9biFZ5gKE-B9r_rQ@mail.gmail.com>
Date:   Fri, 18 Mar 2022 09:14:09 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Joerg Roedel <jroedel@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/sev: Add ENCODE_FRAME_POINTER after stack changed for #VC

On Fri, Mar 18, 2022 at 6:19 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Wed, Mar 16, 2022 at 12:16:12PM +0800, Lai Jiangshan wrote:
> > From: Lai Jiangshan <jiangshan.ljs@...group.com>
> >
> > In idtentry_vc(), the real frame is changed after it switches to new
> > stack, ENCODE_FRAME_POINTER should be called in case for unwinder.
> >
> > Cc: Joerg Roedel <jroedel@...e.de>
> > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> > ---
> >  arch/x86/entry/entry_64.S | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index e20eabaa56b8..f99f2881ed83 100644
> > --- a/arch/x86/entry/entry_64.S
> > +++ b/arch/x86/entry/entry_64.S
> > @@ -540,6 +540,7 @@ SYM_CODE_START(\asmsym)
> >       call    vc_switch_off_ist
> >       movq    %rax, %rsp              /* Switch to new stack */
> >
> > +     ENCODE_FRAME_POINTER
> >       UNWIND_HINT_REGS
> >
> >       /* Update pt_regs */
>
> Looks right to me.  Any chance you have the ability to test this
> scenario by unwinding from #VC with CONFIG_FRAME_POINTER?
>

I don't have the hardware to test it.  Actually, it was you to
inspire me to find this in the conversation of my patchset when
I tried to search all the code of switching of %rsp to see how
ENCODE_FRAME_POINTER and UNWIND_HINT_REGS are used once more.

> --
> Josh
>