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Message-ID: <CAE9FiQW5tSXPZLKB_3xh4TNVgU=vHiMOeUmN9h+nzkg3VTqDXw@mail.gmail.com>
Date: Sat, 6 Aug 2016 21:53:50 -0700
From: Yinghai Lu <yinghai@...nel.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Thomas Garnier <thgarnie@...gle.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Kees Cook <keescook@...omium.org>, 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 v2] x86/power/64: Support unaligned addresses for
temporary mapping
On Sat, Aug 6, 2016 at 6:03 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, August 03, 2016 11:28:48 PM Rafael J. Wysocki wrote:
>
> On a second thought, it seems to be better to follow your suggestion to simply
> provide a special version of kernel_ident_mapping_init() for hibernation,
> because it is sufficiently distinct from the other users of the code in
> ident_map.c.
>
> The patch below does just that (lightly tested).
>
>
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Subject: [PATCH] x86/power/64: Always create temporary identity mapping correctly
>
> The low-level resume-from-hibernation code on x86-64 uses
> kernel_ident_mapping_init() to create the temoprary identity mapping,
> but that function assumes that the offset between kernel virtual
> addresses and physical addresses is aligned on the PGD level.
>
> However, with a randomized identity mapping base, it may be aligned
> on the PUD level and if that happens, the temporary identity mapping
> created by set_up_temporary_mappings() will not reflect the actual
> kernel identity mapping and the image restoration will fail as a
> result (leading to a kernel panic most of the time).
>
> To fix this problem, provide simplified routines for creating the
> temporary identity mapping during resume from hibernation on x86-64
> that support unaligned offsets between KVA and PA up to the PMD
> level.
>
> Although kernel_ident_mapping_init() might be made work in that
> case too, using hibernation-specific code for that is way simpler.
>
> Reported-by: Thomas Garnier <thgarnie@...gle.com>
> Suggested-by: Yinghai Lu <yinghai@...nel.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> arch/x86/power/hibernate_64.c | 61 ++++++++++++++++++++++++++++++++++++------
> 1 file changed, 53 insertions(+), 8 deletions(-)
>
> Index: linux-pm/arch/x86/power/hibernate_64.c
> ===================================================================
> --- linux-pm.orig/arch/x86/power/hibernate_64.c
> +++ linux-pm/arch/x86/power/hibernate_64.c
> @@ -77,18 +77,63 @@ static int set_up_temporary_text_mapping
> return 0;
> }
>
> -static void *alloc_pgt_page(void *context)
> +static void ident_pmd_init(pmd_t *pmd, unsigned long addr, unsigned long end)
> {
> - return (void *)get_safe_page(GFP_ATOMIC);
> + for (; addr < end; addr += PMD_SIZE)
> + set_pmd(pmd + pmd_index(addr),
> + __pmd((addr - __PAGE_OFFSET) | __PAGE_KERNEL_LARGE_EXEC));
> +}
> +
> +static int ident_pud_init(pud_t *pud, unsigned long addr, unsigned long end)
> +{
> + unsigned long next;
> +
> + for (; addr < end; addr = next) {
> + pmd_t *pmd;
> +
> + pmd = (pmd_t *)get_safe_page(GFP_ATOMIC);
> + if (!pmd)
> + return -ENOMEM;
> +
> + next = (addr & PUD_MASK) + PUD_SIZE;
> + if (next > end)
> + next = end;
> +
> + ident_pmd_init(pmd, addr & PMD_MASK, next);
> + set_pud(pud + pud_index(addr), __pud(__pa(pmd) | _KERNPG_TABLE));
> + }
> + return 0;
> +}
> +
> +static int ident_mapping_init(pgd_t *pgd, unsigned long mstart, unsigned long mend)
> +{
> + unsigned long addr = mstart + __PAGE_OFFSET;
> + unsigned long end = mend + __PAGE_OFFSET;
> + unsigned long next;
> +
> + for (; addr < end; addr = next) {
> + pud_t *pud;
> + int result;
> +
> + pud = (pud_t *)get_safe_page(GFP_ATOMIC);
> + if (!pud)
> + return -ENOMEM;
> +
> + next = (addr & PGDIR_MASK) + PGDIR_SIZE;
> + if (next > end)
> + next = end;
> +
> + result = ident_pud_init(pud, addr, next);
> + if (result)
> + return result;
> +
> + set_pgd(pgd + pgd_index(addr), __pgd(__pa(pud) | _KERNPG_TABLE));
> + }
> + return 0;
> }
>
> static int set_up_temporary_mappings(void)
> {
> - struct x86_mapping_info info = {
> - .alloc_pgt_page = alloc_pgt_page,
> - .pmd_flag = __PAGE_KERNEL_LARGE_EXEC,
> - .kernel_mapping = true,
> - };
> unsigned long mstart, mend;
> pgd_t *pgd;
> int result;
> @@ -108,7 +153,7 @@ static int set_up_temporary_mappings(voi
> mstart = pfn_mapped[i].start << PAGE_SHIFT;
> mend = pfn_mapped[i].end << PAGE_SHIFT;
>
> - result = kernel_ident_mapping_init(&info, pgd, mstart, mend);
> + result = ident_mapping_init(pgd, mstart, mend);
> if (result)
> return result;
> }
>
Hi Rafael,
Your version seems not considering different pfn_mapped range could
share same PGD (512G) or even PUD(1G), or even same PMD (2M) range.
so just keep on using kernel_ident_mapping_init() for that.
At the same time, set_up_temporary_text_mapping could be replaced with
kernel_ident_mapping_init() too if restore_jump_address is KVA for
jump_address_phys.
Thanks
Yinghai
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