Re: [PATCH] efi_loader: Get rid of kaslr-seed

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hi Heinrich, 
On Thu, Dec 16, 2021 at 04:59:02PM +0100, Heinrich Schuchardt wrote:
> On 12/16/21 16:48, Mark Kettenis wrote:
> > > From: Ard Biesheuvel <ardb@kernel.org>
> > > Date: Thu, 16 Dec 2021 16:28:06 +0100
> > > 
> > > On Thu, 16 Dec 2021 at 16:25, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> > > > 
> > > > > From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> > > > > Date: Thu, 16 Dec 2021 16:52:08 +0200
> > > > > 
> > > > > Right now we unconditionally pass a 'kaslr-seed' property to the kernel
> > > > > if the DTB we ended up in EFI includes the entry.  However the kernel
> > > > > EFI stub completely ignores it and only relies on EFI_RNG_PROTOCOL.
> > > > > So let's get rid of it unconditionally since it would mess up the
> > > > > (upcoming) DTB TPM measuring as well.
> > > > 
> > > > NAK
> > > > 
> > > > OpenBSD uses the kaslr-seed property in the bootloader to mix in some
> > > > additional entropy.  (It will also use EFI_RNG_PROTOCOL if it is
> > > > avilable, but most U-Boot boards don't provide that, or at least not
> > > > yet).
> > > > 
> > > 
> > > What is the point of using both the DT property and the protocol if
> > > both are available?
> > 
> > Unless kaslr-seed is coming from a different entropy source, there
> > probably isn't a point.  But it doesn't hurt and it made the
> > bootloader code simpler.
> > 
> > It does mean there is some room for compromise though.  If U-Boot
> > would only remove kaslr-seed if it implements EFI_RNG_PROTOCOL it
> > wouldn't be a problem.
> 

I can limit the stripping if EFI_RNG_PROTOCOL is installed or a specific
Kconfig option is selected and hopefully we can get rid of the Kconfig in
the future. 

> Only QEMU's ARM virt machine fills kaslr-seed in the device-tree.
> 

U-Boot injects it as well in some cases e,g sec_firmware_get_random()

[...]

Regards
/Ilias