Re: [PATCH] x86/kexec: Push kjump return address even for non-kjump kexec

[Dave Hansen]

On 4/2/26 03:34, David Woodhouse wrote:
> The version of purgatory code shipped by kexec-tools attempts to look
> above the top of its stack to find a return address for a kjump

This is a bug in kexec-tools, right? Has kexec-tools been fixed?

The purgatory code is injected by userspace, so are you kinda asserting
here that the this change in the kernel stack "breaks userspace"?

I guess one little push isn't the end of the world. But, can we please
comment it to this effect:

	/*
	 * Work around a kexec-tools' <version here> purgatory bug that
	 * accesses the stack one long out of bounds. Push a dummy value
	 * to make the access harmless and avoid a fault.
	 */

Without that, we'll be scratching our heads for the next decade about
what this 0 on the stack does. The comment you suggested tells us what
it is doing, but not why.

It all feels kinda icky though. Our stack is an ABI?!?!?!