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From:   Mathieu Malaterre <malat@debian.org>
Date:   Wed, 5 Jun 2019 13:32:39 +0200
Message-ID: <CA+7wUswvw3JJ2dLCn877tNbTd==O5c9LxHGezOm+y5otQZnS2w@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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Sender: linux-kernel-owner@vger.kernel.org
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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>

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
>