linux-kernel - Re: [RFC PATCH] kexec, x86/boot: map systab region in identity mapping before accessing it

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Message-ID: <20190422143346.GD3584@localhost.localdomain>
Date:   Mon, 22 Apr 2019 22:33:46 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Junichi Nomura <j-nomura@...jp.nec.com>,
        Borislav Petkov <bp@...en8.de>, dyoung@...hat.com
Cc:     Kairui Song <kasong@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Chao Fan <fanc.fnst@...fujitsu.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>
Subject: Re: [RFC PATCH] kexec, x86/boot: map systab region in identity
 mapping before accessing it

On 04/19/19 at 01:36pm, Borislav Petkov wrote:
> On Fri, Apr 19, 2019 at 01:28:01PM +0200, Borislav Petkov wrote:
> > Read again what I said: "should all be passed through boot_params".
> > Which means, boot_params should be extended with a field of a flag to
> > say: "this is a kexec'ed kernel".
> 
> And by that I mean similar to the XLF_EFI_KEXEC mechanism. The first
> kernel or kexec(1) should prepare the info needed by the kexec'ed
> kernel.

We have set the loader type to '0x0D << 4' for kexec specifically, in both
kexec_load and kexec_file_load. We can check this to identify if it's
kexec-ed kernel or not.

Update patch with it?

static void *bzImage64_load(struct kimage *image, char *kernel,
                            unsigned long kernel_len, char *initrd,
                            unsigned long initrd_len, char *cmdline,
                            unsigned long cmdline_len)
{

	...
	/* bootloader info. Do we need a separate ID for kexec kernel loader? */
        params->hdr.type_of_loader = 0x0D << 4;
	...

}