linux-kernel - Re: [PATCH] x86/tdx: Do not corrupt frame-pointer in __tdx

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Message-ID: <20230131083901.ssg5huno2lhrbmzg@box.shutemov.name>
Date:   Tue, 31 Jan 2023 11:39:01 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] x86/tdx: Do not corrupt frame-pointer in
 __tdx_hypercall()

On Tue, Jan 31, 2023 at 09:34:12AM +0100, Peter Zijlstra wrote:
> On Mon, Jan 30, 2023 at 04:53:54PM +0300, Kirill A. Shutemov wrote:
> > If compiled with CONFIG_FRAME_POINTER=y, objtool in not happy that
> > __tdx_hypercall() messes up RBP.
> > 
> >   objtool: __tdx_hypercall+0x7f: return with modified stack frame
> > 
> > Rework the function to store TDX_HCALL_ flags on stack instead of RBP.
> 
> Also, on IRC you mentioned that per TDX spec, BP is a valid argument
> register too and you were going to raise this and get it fixed, TDX
> hypercalls must not use BP to pass data.

I've raised the question yesterday. No progress so far. It will take time
to get it into the public spec.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov