linux-kernel - Re: [PATCH v2] x86: selective remapping in parse_setup

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Date:	Mon, 12 Aug 2013 16:30:05 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Linn Crosetto <linn@...com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Jacob Shin <jacob.shin@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86: selective remapping in parse_setup_data()

On Mon, Aug 12, 2013 at 4:01 PM, Linn Crosetto <linn@...com> wrote:
> Type SETUP_PCI, added by setup_efi_pci(), may advertise a ROM size
> larger than early_memremap() is able to handle, which is currently
> limited to 256kB. If this occurs it leads to a NULL dereference in
> parse_setup_data().
>
> To avoid this, first remap the setup_data header, and remap the data
> only for types actually parsed in parse_setup_data(). Type SETUP_PCI is
> handled later by pcibios_add_device(), when ioremap() is available.
>
> Signed-off-by: Linn Crosetto <linn@...com>
> ---
> v2: add more detail to the explanation as requested by hpa
> ---
>  arch/x86/kernel/setup.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index f8ec578..2063a49 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -423,6 +423,17 @@ static void __init reserve_initrd(void)
>  }
>  #endif /* CONFIG_BLK_DEV_INITRD */
>
> +static void __init remap_setup_data(u64 pa_data, u32 data_len,
> +                                   struct setup_data **data, u32 *map_len)
> +{
> +       if (data_len <= *map_len)
> +               return;
> +
> +       early_iounmap(*data, *map_len);
> +       *data = early_memremap(pa_data, data_len);
> +       *map_len = data_len;
> +}
> +
>  static void __init parse_setup_data(void)
>  {
>         struct setup_data *data;
> @@ -432,18 +443,16 @@ static void __init parse_setup_data(void)
>         while (pa_data) {
>                 u32 data_len, map_len;
>
> +               /* The data length may be too large for early remapping,
> +                  remap the data only when needed. */
>                 map_len = max(PAGE_SIZE - (pa_data & ~PAGE_MASK),
>                               (u64)sizeof(struct setup_data));
>                 data = early_memremap(pa_data, map_len);
>                 data_len = data->len + sizeof(struct setup_data);
> -               if (data_len > map_len) {
> -                       early_iounmap(data, map_len);
> -                       data = early_memremap(pa_data, data_len);
> -                       map_len = data_len;
> -               }
>
>                 switch (data->type) {
>                 case SETUP_E820_EXT:
> +                       remap_setup_data(pa_data, data_len, &data, &map_len);
>                         parse_e820_ext(data);
>                         break;
>                 case SETUP_DTB:

how about just passing phys_addr and length with parse_e820_ext and parse_dtb?
let them to worry about length and handle oversize case.

Thanks

Yinghai
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