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SubjectRe: [PATCH 10/11] kexec: Support for loading ELF x86_64 images
On Fri, Mar 07, 2014 at 06:12:33PM +0100, Borislav Petkov wrote:
> > > > +/* Fill in fields which are usually present in bzImage */
> > > > +static int init_linux_parameters(struct boot_params *params)
> > > > +{
> > > > + /*
> > > > + * FIXME: It is odd that the information which comes from kernel
> > > > + * has to be faked by loading kernel. I guess it is limitation of
> > > > + * ELF format. Right now keeping it same as kexec-tools
> > > > + * implementation. But this most likely needs fixing.
> > > > + */
> > > > + memcpy(&params->hdr.header, "HdrS", 4);
> > > > + params->hdr.version = 0x0206;
> > > > + params->hdr.initrd_addr_max = 0x37FFFFFF;
> > > > + params->hdr.cmdline_size = 2048;
> > > > + return 0;
> > > > +}

...

> Well, this is mandated by the boot protocol, no?
>
> "If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
> the boot protocol version is "old". Loading an old kernel, the
> following parameters should be assumed:
>
> Image type = zImage
> initrd not supported
> Real-mode kernel must be located at 0x90000."
>
> About version 0x0206:
>
> Field name: cmdline_size
> Type: read
> Offset/size: 0x238/4
> Protocol: 2.06+
>
> The maximum size of the command line without the terminating
> zero. This means that the command line can contain at most
> cmdline_size characters. With protocol version 2.05 and earlier, the
> maximum size was 255.
>
> So according to the protocol, cmdline_size should be set by
> kexec_file_load and not hardcoded to 2K, if we're mandating protocol
> version 2.06.

Btw, all those fields above are of type "read", which means,

"For each field, some are information from the kernel to the bootloader
("read"),... "

Now, if we assume that the first kernel is the bootloader and it loads
the second kernel, then the first kernel shouldn't be setting all those
fields *at* *all* because it violates the boot protocol. And that's a
no-no.

Generally, how important is that use case for loading ELF images? If no
one is actually using it, why even bother?

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--


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