linux-kernel - Re: [PATCH 1/2] x86/sysfb: add support for 64bit EFI lfb

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Date:   Tue, 15 Nov 2016 13:08:42 +0100
From:   Tom Gundersen <teg@...m.no>
To:     David Herrmann <dh.herrmann@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Matt Fleming <matt.fleming@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] x86/sysfb: add support for 64bit EFI lfb_base

On Tue, Nov 15, 2016 at 1:01 PM, David Herrmann <dh.herrmann@...il.com> wrote:
> The screen_info object was extended to support 64bit lfb_base addresses
> in:
>
>     commit ae2ee627dc87a70910de91b791b3cd0e9c6facdd
>     Author: Matt Fleming <matt.fleming@...el.com>
>     Date:   Tue Aug 25 16:32:55 2015 +0100
>
>         efifb: Add support for 64-bit frame buffer addresses
>
> However, the x86 simple-framebuffer setup code never made use of it. Fix
> it to properly assemble and verify the lfb_base before advertising
> simple-framebuffer devices.
>
> In particular, this means if VIDEO_CAPABILITY_64BIT_BASE is set, the
> screen_info->ext_lfb_base field will contain the upper 32bit of the
> actual lfb_base. Make sure the address is not 0 (i.e., unset), as well as
> does not overflow the physical address type.
>
> Signed-off-by: David Herrmann <dh.herrmann@...il.com>

Reviewed-by: Tom Gundersen <teg@...m.no>

> ---
>  arch/x86/kernel/sysfb_simplefb.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/sysfb_simplefb.c b/arch/x86/kernel/sysfb_simplefb.c
> index 764a29f..35b8641 100644
> --- a/arch/x86/kernel/sysfb_simplefb.c
> +++ b/arch/x86/kernel/sysfb_simplefb.c
> @@ -67,6 +67,20 @@ __init int create_simplefb(const struct screen_info *si,
>         struct platform_device *pd;
>         struct resource res;
>         unsigned long len;
> +       u64 base;
> +
> +       /*
> +        * If the 64BIT_BASE capability is set, ext_lfb_base will contain the
> +        * upper half of the base address. Assemble the address, then make sure
> +        * it is valid and we can actually access it.
> +        */
> +       base = si->lfb_base;
> +       if (si->capabilities & VIDEO_CAPABILITY_64BIT_BASE)
> +               base |= (u64)si->ext_lfb_base << 32;
> +       if (!base || (u64)(resource_size_t)base != base) {
> +               printk(KERN_DEBUG "sysfb: inaccessible VRAM base\n");
> +               return -EINVAL;
> +       }
>
>         /* don't use lfb_size as it may contain the whole VMEM instead of only
>          * the part that is occupied by the framebuffer */
> @@ -81,8 +95,8 @@ __init int create_simplefb(const struct screen_info *si,
>         memset(&res, 0, sizeof(res));
>         res.flags = IORESOURCE_MEM | IORESOURCE_BUSY;
>         res.name = simplefb_resname;
> -       res.start = si->lfb_base;
> -       res.end = si->lfb_base + len - 1;
> +       res.start = base;
> +       res.end = res.start + len - 1;
>         if (res.end <= res.start)
>                 return -EINVAL;
>
> --
> 2.10.2
>