On Wed, Dec 22, 2021 at 10:30 AM Ard Biesheuvel [off-list ref] wrote:

On Wed, 22 Dec 2021 at 03:31, Linus Walleij [off-list ref] wrote:

quoted

On Tue, Dec 21, 2021 at 10:16 AM Arnd Bergmann [off-list ref] wrote:

quoted

I think for CPUs that can use LPAE, we want to eventually move to the 4G:4G
memory model, which in turn depends on having the kernel in vmalloc space, as
implemented by Linus Walleij in
https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git/log/?h=kernel-in-vmalloc-v5.14-rc1

Yeah I'm still working on this series. The 4/4 split works pretty well,

Actually it's just kernel-in-vmalloc, 4/4 comes after that.

quoted

but it breaks KASan and I was in the process of fixing that when I left
for parental leave.

The reason it breaks would be related to KASan not expecting
executable code in the vmalloc area, and since the shadowing
algorithm is a simple pointer offset, and since we go to lengths
to chisel shadow memory out of lowmem at a fixed offset from
TEXT_OFFSET, we have a problem.

Vmap'ed stacks actually has a similar problem, which is why it is
disabled when KAsan is enabled. But this can be fixed by enabling arch
support for KASAN_VMALLOC, and I suspect it may address the vmap'ed
kernel as well.

Yep after seeing the other convo on the topic I realized that this
is indeed the same as I'm seeing. I can't disable KASAN just
because the kernel is in VMALLOC though, so I suppose when
I finally get back to this I have to fix KASAN_VMALLOC too
if noone beats me to it.

(It'd be great if someone could beat me to it...)

Yours,
Linus Walleij

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