Re: [PATCH v4 3/4] x86/uaccess: Use pointer masking to limit uaccess speculation

[Linus Torvalds]

On Wed, May 5, 2021 at 1:48 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> This would error requests for address 0 earlier - but I don't
> believe they are ever valid in Linux.
> (Some historic x86 a.out formats did load to address 0.)

Not only loading at address 0 - there are various real reason s why
address 0 might actually be needed.

Anybody who still runs a 32-bit kernel and wants to use vm86 mode, for
example, requires address 0 because that's simply how the hardware
works.

So no. "mask to zero and make zero invalid" is not a proper model.

            Linus