Re: [4.19.y PATCH 1/3] efi/x86/Add missing error handling to old_memmap 1:1 mapping code

Greg KH
2019-06-29T06:57:25Z

On Fri, Jun 28, 2019 at 11:42:13AM -0700, Srivatsa S. Bhat wrote:
> From: Gen Zhang <blackgod016574@gmail.com>
>
> commit 4e78921ba4dd0aca1cc89168f45039add4183f8e upstream.
>
> The old_memmap flow in efi_call_phys_prolog() performs numerous memory
> allocations, and either does not check for failure at all, or it does
> but fails to propagate it back to the caller, which may end up calling
> into the firmware with an incomplete 1:1 mapping.
>
> So let's fix this by returning NULL from efi_call_phys_prolog() on
> memory allocation failures only, and by handling this condition in the
> caller. Also, clean up any half baked sets of page tables that we may
> have created before returning with a NULL return value.
>
> Note that any failure at this level will trigger a panic() two levels
> up, so none of this makes a huge difference, but it is a nice cleanup
> nonetheless.

With a description like this, why is this needed in a stable kernel if
it does not really fix anything useful?

thanks,

greg k-h