linux-kernel - Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on kexec-ed kernel

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Date:   Fri, 12 Apr 2019 15:35:29 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     Dave Young <dyoung@...hat.com>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Baoquan He <bhe@...hat.com>, Kairui Song <kasong@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on
 kexec-ed kernel

On Fri, Apr 12, 2019 at 10:49:56AM +0200, Borislav Petkov wrote:
> Now I need to go figure out whether there's a reliable way to know in
> the kexec kernel that it *is* a kexec kernel.

Actually, thinking about this more, we don't need to know whether the
kernel was kexeced or not. Why?

Because if it is kexec'ed, kexec(1) passes the required info in
setup_data. Now, if for whatever reason the kexec'ed kernel fails to
parse that EFI info and get the systab to figure out the RDSP, then it
doesn't have any other choice but fail booting.

Because there's no way it can figure out where the EFI runtime has been
mapped and recover by finding the RDSP from there.

So I think we're perfectly fine with the old approach:

        if (!pa)
                pa = kexec_get_rsdp_addr();

        if (!pa)
                pa = efi_get_rsdp_addr();

-- 
Regards/Gruss,
    Boris.

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