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SubjectRe: [RFC PATCH] kexec, x86/boot: map systab region in identity mapping before accessing it
On 04/22/19 at 05:17pm, Borislav Petkov wrote:
> + 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.

Yes, agree. Time has proved we don't need a separate ID, just 0x0D is
fine for both kexec/kdump. We can clear it away now.

I can make a patch to add a bit into xloadflags, to indicate that this
is kexec-ed kernel. It can help to differentiate kexec-ed kernel from
kdump kernel. As we know, kdump kernel is recognized with /proc/vmcore
existence. While during kernel initialization stage, or /proc/vmcore is
not validated in some cases, the adding bit may help.

Thoughts?

Thanks
Baoquan

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