[PATCH v3 4/4] ARM: Implement PAN for LPAE by TTBR0 page table walks disablement

[Geert Uytterhoeven]

Hi Ard,

On Tue, May 14, 2024 at 9:59 AM Ard Biesheuvel <ardb at kernel.org> wrote:
> On Tue, 14 May 2024 at 09:46, Linus Walleij <linus.walleij at linaro.org> wrote:
> > On Tue, May 14, 2024 at 8:41 AM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> >
> > > I sent you a small initramfs by PM.
> >
> > Booted this just fine on Vexpress QEMU:
> >
> > Run /init as init process
> > sysctl: error: 'kernel.hotplug' is an unknown key
> >
> >
> > boot (Linux 6.9.0-rc1+, BusyBox v1.16.0.git, kexec-tools 2.0.1-git)
> > / # mount -t debugfs none /sys/kernel/debug
> > / # echo "ACCESS_USERSPACE" | cat >/sys/kernel/debug/provoke-crash/DIRECT
> > lkdtm: Performing direct entry ACCESS_USERSPACE
> > lkdtm: attempting bad read at 76fea000
> > 8<--- cut here ---
> > Unable to handle kernel paging request at virtual address 76fea000 when read
> > [76fea000] *pgd=82c93003, *pmd=82c94003, *pte=a00000811e2f5f
> > Internal error: Oops: 206 [#1] SMP ARM
> > CPU: 1 PID: 86 Comm: cat Not tainted 6.9.0-rc1+ #46
> > Hardware name: ARM-Versatile Express
> > PC is at lkdtm_ACCESS_USERSPACE+0xc0/0x138
> > LR is at lkdtm_ACCESS_USERSPACE+0xc0/0x138
> >
> > I'm starting to think it is something about different LPAE implementations here.
> >
>
> I have built multi_v7_defconfig with the following enabled
>
> CONFIG_ARM_LPAE=y
> CONFIG_CPU_TTBR0_PAN=y
> CONFIG_LKDTM=y
>
> and the resulting kernel boots happily as a 32-bit VM running under a
> Rpi4 KVM host.
>
> Could someone post an actual .config that reproduces this? Rpi4 is
> A72, which both works and doesn't work in Florian's testing, so I'd be
> highly surprised if this is not a config issue.

shmobile_defconfig with CONFIG_LPAE=y added failed for me before.

Building multi_v7_defconfig with the above enabled...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds