On Wed, Jun 5, 2019 at 1:32 PM Mathieu Malaterre <ma...@debian.org> wrote:
>
> On Mon, Jun 3, 2019 at 3:00 PM Christophe Leroy <christophe.le...@c-s.fr>
> wrote:
> >
> > When booting through OF, setup_disp_bat() does nothing because
> > disp_BAT are not set. By change, it used to work because BOOTX
> > buffer is mapped 1:1 at address 0x81000000 by the bootloader, and
> > btext_setup_display() sets virt addr same as phys addr.
> >
> > But since commit 215b823707ce ("powerpc/32s: set up an early static
> > hash table for KASAN."), a temporary page table overrides the
> > bootloader mapping.
> >
> > This 0x81000000 is also problematic with the newly implemented
> > Kernel Userspace Access Protection (KUAP) because it is within user
> > address space.
> >
> > This patch fixes those issues by properly setting disp_BAT through
> > a call to btext_prepare_BAT(), allowing setup_disp_bat() to
> > properly setup BAT3 for early bootx screen buffer access.
> >
> > Reported-by: Mathieu Malaterre <ma...@debian.org>
> > Fixes: 215b823707ce ("powerpc/32s: set up an early static hash table for
> > KASAN.")
> > Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
>
> The patch below does fix the symptoms I reported. Tested with CONFIG_KASAN=n :
>
> Tested-by: Mathieu Malaterre <ma...@debian.org>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=203699
>
> Thanks !
>
> > ---
> > arch/powerpc/include/asm/btext.h | 4 ++++
> > arch/powerpc/kernel/prom_init.c | 1 +
> > arch/powerpc/kernel/prom_init_check.sh | 2 +-
> > 3 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/include/asm/btext.h
> > b/arch/powerpc/include/asm/btext.h
> > index 3ffad030393c..461b0f193864 100644
> > --- a/arch/powerpc/include/asm/btext.h
> > +++ b/arch/powerpc/include/asm/btext.h
> > @@ -13,7 +13,11 @@ extern void btext_update_display(unsigned long phys, int
> > width, int height,
> > int depth, int pitch);
> > extern void btext_setup_display(int width, int height, int depth, int
> > pitch,
> > unsigned long address);
> > +#ifdef CONFIG_PPC32
> > extern void btext_prepare_BAT(void);
> > +#else
> > +static inline void btext_prepare_BAT(void) { }
> > +#endif
> > extern void btext_map(void);
> > extern void btext_unmap(void);
> >
> > diff --git a/arch/powerpc/kernel/prom_init.c
> > b/arch/powerpc/kernel/prom_init.c
> > index 3555cad7bdde..ed446b7ea164 100644
> > --- a/arch/powerpc/kernel/prom_init.c
> > +++ b/arch/powerpc/kernel/prom_init.c
> > @@ -2336,6 +2336,7 @@ static void __init prom_check_displays(void)
> > prom_printf("W=%d H=%d LB=%d addr=0x%x\n",
> > width, height, pitch, addr);
> > btext_setup_display(width, height, 8, pitch, addr);
> > + btext_prepare_BAT();
> > }
> > #endif /* CONFIG_PPC_EARLY_DEBUG_BOOTX */
> > }
> > diff --git a/arch/powerpc/kernel/prom_init_check.sh
> > b/arch/powerpc/kernel/prom_init_check.sh
> > index 518d416971c1..160bef0d553d 100644
> > --- a/arch/powerpc/kernel/prom_init_check.sh
> > +++ b/arch/powerpc/kernel/prom_init_check.sh
> > @@ -24,7 +24,7 @@ fi
> > WHITELIST="add_reloc_offset __bss_start __bss_stop copy_and_flush
> > _end enter_prom $MEM_FUNCS reloc_offset __secondary_hold
> > __secondary_hold_acknowledge __secondary_hold_spinloop __start
> > -logo_linux_clut224
> > +logo_linux_clut224 btext_prepare_BAT
> > reloc_got2 kernstart_addr memstart_addr linux_banner _stext
> > __prom_init_toc_start __prom_init_toc_end btext_setup_display TOC."
> >
> > --
> > 2.13.3
> >
