linux-kernel - Re: [PATCH v8 00/23] efi/x86: Avoid bare metal decompressor during EFI boot

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Message-ID: <CAMj1kXHi8=L8e=a5ci4yQFVrc=XqqJaMNvZuPXduwaAVfmm4_Q@mail.gmail.com>
Date:   Sun, 6 Aug 2023 12:05:25 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Evgeniy Baskov <baskov@...ras.ru>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Mario Limonciello <mario.limonciello@....com>,
        Kees Cook <keescook@...omium.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v8 00/23] efi/x86: Avoid bare metal decompressor during
 EFI boot

On Sun, 6 Aug 2023 at 00:19, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Sat, 5 Aug 2023 at 23:07, Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Sat, Aug 05, 2023 at 07:37:17PM +0200, Ard Biesheuvel wrote:
> > > So this is the host booting, right?
> >
> > Yes.
> >
> > > So is the position of the C bit perhaps getting detect incorrectly?
> >
> > I don't know yet. But the evildoer is someone else:
> >
> > 02d47ce2ae02 ("x86/head_64: Store boot_params pointer in callee save register")
> >
> > after bisection. More staring later as to why...
> >
>
> How bizarre.
>
> But that was a bonus patch anyway, so we could just drop it for now.

I suspect this should fix the issue:

--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -110,6 +110,7 @@ SYM_CODE_START_NOALIGN(startup_64)
         * programmed into CR3.
         */
        leaq    _text(%rip), %rdi
+       movq    %r15, %rsi
        call    __startup_64

        /* Form the CR3 value being sure to include the CR3 modifier */