linux-kernel - Re: [PATCH v1 1/2] x86/power/64: Support unaligned addresses for temporary mapping

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Message-ID: <CAE9FiQXPnXa_Ep2nk+y5boZ9Csdk_yoH5Ws8SaExn0-VHU9bBg@mail.gmail.com>
Date:	Tue, 2 Aug 2016 10:36:27 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v1 1/2] x86/power/64: Support unaligned addresses for
 temporary mapping

On Mon, Aug 1, 2016 at 10:07 AM, Thomas Garnier <thgarnie@...gle.com> wrote:
> Correctly setup the temporary mapping for hibernation. Previous
> implementation assumed the address was aligned on the PGD level. With
> KASLR memory randomization enabled, the address is randomized on the PUD
> level. This change supports unaligned address up to PMD.
>
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> ---
>  arch/x86/mm/ident_map.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
> index ec21796..ea1ebf1 100644
> --- a/arch/x86/mm/ident_map.c
> +++ b/arch/x86/mm/ident_map.c
> @@ -3,15 +3,16 @@
>   * included by both the compressed kernel and the regular kernel.
>   */
>
> -static void ident_pmd_init(unsigned long pmd_flag, pmd_t *pmd_page,
> +static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
>                            unsigned long addr, unsigned long end)
>  {
> -       addr &= PMD_MASK;
> -       for (; addr < end; addr += PMD_SIZE) {
> -               pmd_t *pmd = pmd_page + pmd_index(addr);
> +       int off = info->kernel_mapping ? pmd_index(__PAGE_OFFSET) : 0;
> +
> +       for (addr &= PMD_MASK; addr < end; addr += PMD_SIZE) {
> +               pmd_t *pmd = pmd_page + pmd_index(addr) + off;
>
>                 if (!pmd_present(*pmd))
> -                       set_pmd(pmd, __pmd(addr | pmd_flag));
> +                       set_pmd(pmd, __pmd(addr | info->pmd_flag));
>         }
>  }
>
> @@ -19,9 +20,10 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
>                           unsigned long addr, unsigned long end)
>  {
>         unsigned long next;
> +       int off = info->kernel_mapping ? pud_index(__PAGE_OFFSET) : 0;
>
>         for (; addr < end; addr = next) {
> -               pud_t *pud = pud_page + pud_index(addr);
> +               pud_t *pud = pud_page + pud_index(addr) + off;
>                 pmd_t *pmd;
>
>                 next = (addr & PUD_MASK) + PUD_SIZE;

Is there any chance for (pud_index(addr) + off) or (pmd_index(addr) + off)
bigger than 512?

Looks like we need to change the loop from phys address to virtual
address instead.
to avoid the overflow.

Thanks

Yinghai