Re: [PATCH qemu] x86: don't let decompressed kernel image clobber setup_data

[Philippe Mathieu-Daudé]

On 29/12/22 03:31, Jason A. Donenfeld wrote:
> Hi,
>
> Read this message in a fixed width text editor with a lot of columns.
>
> On Wed, Dec 28, 2022 at 03:58:12PM -0800, H. Peter Anvin wrote:
> > Glad you asked.
> >
> > So the kernel load addresses are parameterized in the kernel image
> > setup header. One of the things that are so parameterized are the size
> > and possible realignment of the kernel image in memory.
> >
> > I'm very confused where you are getting the 64 MB number from. There
> > should not be any such limitation.

[...]

Thanks for the diagrams. Feel free to include them in the commit
description ;)

> > In general, setup_data should be able to go anywhere the initrd can
> > go, and so is subject to the same address cap (896 MB for old kernels,
> > 4 GB on newer ones; this address too is enumerated in the header.)
>
> It would be theoretically possible to attach it to the initrd image
> instead of to the kernel image. As a last resort, I guess I can look
> into doing that. However, that's going to require some serious rework
> and plumbing of a lot of different components. So if I can make it work
> as is, that'd be ideal. However, I need to figure out this weird 62 meg
> limitation.
>
> Any ideas on that?

Could it be a limitation (internal buffer) of the decompressor?