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

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Message-ID: <CAJcbSZE1kPpL_hWLK70fGhgjP3xRBaZ=r32E9q1SBwhCbqOp5Q@mail.gmail.com>
Date:	Tue, 2 Aug 2016 10:48:01 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
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 Tue, Aug 2, 2016 at 10:36 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> 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.
>

That's a good point. I will take a look at it.

> Thanks
>
> Yinghai