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

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Message-ID: <20190422151723.GD21457@zn.tnic>
Date:   Mon, 22 Apr 2019 17:17:23 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Baoquan He <bhe@...hat.com>, "H. Peter Anvin" <hpa@...or.com>
Cc:     Junichi Nomura <j-nomura@...jp.nec.com>, dyoung@...hat.com,
        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

+ hpa

On Mon, Apr 22, 2019 at 10:33:46PM +0800, Baoquan He wrote:
> 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;

That's already documented in Documentation/x86/boot.txt

Field name:     type_of_loader
Type:           write (obligatory)
Offset/size:    0x210/1
Protocol:       2.00+

	...

        D  kexec-tools

And yes, the question in the code is still valid: do we need a separate ID.

I'd say no and we'll simply call 0xD all kernels loaded using a
kexec-type syscall.

IMO.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.