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From:   Mathieu Malaterre <malat@debian.org>
Date:   Fri, 7 Jun 2019 08:16:01 +0200
Message-ID: <CA+7wUsx+SfuFJRjm5vByL++7TMr+F3OE_ZT0rNKOf1dMzuJAHg@mail.gmail.com>
Subject: Re: [PATCH] powerpc/32s: fix booting with CONFIG_PPC_EARLY_DEBUG_BOOTX
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        LKML <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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On Wed, Jun 5, 2019 at 1:32 PM Mathieu Malaterre <malat@debian.org> wrote:
>
> On Mon, Jun 3, 2019 at 3:00 PM Christophe Leroy <christophe.leroy@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 <malat@debian.org>
> > Fixes: 215b823707ce ("powerpc/32s: set up an early static hash table for KASAN.")
> > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>
> The patch below does fix the symptoms I reported. Tested with CONFIG_KASAN=n :
>
> Tested-by: Mathieu Malaterre <malat@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
> >