linux-kernel - Re: [PATCH v2] x86/power/64: Support unaligned addresses for temporary mapping

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Message-ID: <CAE9FiQXMJB4rxAanWxAFtXKYUG6WhDbDq+VHQ7eeEuUuy6oD3w@mail.gmail.com>
Date:	Mon, 8 Aug 2016 00:23:33 -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 Mon, Aug 8, 2016 at 12:06 AM, Yinghai Lu <yinghai@...nel.org> wrote:
>>
>>> 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.
>>
>> I see no reason to do that.
>>
>> First, it is not guaranteed that restore_jump_address will always be a KVA for
>> jump_address_phys and second, it really is only necessary to map one PMD in
>> there.
>
> With your v2 version, you could pass difference between restore_jump_address and
> jump_address_phys as info->off ?
> With that, we can kill more lines if replace with
> set_up_temporary_text_mapping with
> kernel_ident_mapping_init() and make code more readable.
>
> But just keep that in separated patch after your v2 patch.

like:

---
 arch/x86/power/hibernate_64.c |   55 ++++++++++++------------------------------
 1 file changed, 17 insertions(+), 38 deletions(-)

Index: linux-2.6/arch/x86/power/hibernate_64.c
===================================================================
--- linux-2.6.orig/arch/x86/power/hibernate_64.c
+++ linux-2.6/arch/x86/power/hibernate_64.c
@@ -41,42 +41,6 @@ unsigned long temp_level4_pgt __visible;

 unsigned long relocated_restore_code __visible;

-static int set_up_temporary_text_mapping(pgd_t *pgd)
-{
-    pmd_t *pmd;
-    pud_t *pud;
-
-    /*
-     * The new mapping only has to cover the page containing the image
-     * kernel's entry point (jump_address_phys), because the switch over to
-     * it is carried out by relocated code running from a page allocated
-     * specifically for this purpose and covered by the identity mapping, so
-     * the temporary kernel text mapping is only needed for the final jump.
-     * Moreover, in that mapping the virtual address of the image kernel's
-     * entry point must be the same as its virtual address in the image
-     * kernel (restore_jump_address), so the image kernel's
-     * restore_registers() code doesn't find itself in a different area of
-     * the virtual address space after switching over to the original page
-     * tables used by the image kernel.
-     */
-    pud = (pud_t *)get_safe_page(GFP_ATOMIC);
-    if (!pud)
-        return -ENOMEM;
-
-    pmd = (pmd_t *)get_safe_page(GFP_ATOMIC);
-    if (!pmd)
-        return -ENOMEM;
-
-    set_pmd(pmd + pmd_index(restore_jump_address),
-        __pmd((jump_address_phys & PMD_MASK) | __PAGE_KERNEL_LARGE_EXEC));
-    set_pud(pud + pud_index(restore_jump_address),
-        __pud(__pa(pmd) | _KERNPG_TABLE));
-    set_pgd(pgd + pgd_index(restore_jump_address),
-        __pgd(__pa(pud) | _KERNPG_TABLE));
-
-    return 0;
-}
-
 static void *alloc_pgt_page(void *context)
 {
     return (void *)get_safe_page(GFP_ATOMIC);
@@ -87,7 +51,6 @@ static int set_up_temporary_mappings(voi
     struct x86_mapping_info info = {
         .alloc_pgt_page    = alloc_pgt_page,
         .pmd_flag    = __PAGE_KERNEL_LARGE_EXEC,
-        .offset        = __PAGE_OFFSET,
     };
     unsigned long mstart, mend;
     pgd_t *pgd;
@@ -99,11 +62,27 @@ static int set_up_temporary_mappings(voi
         return -ENOMEM;

     /* Prepare a temporary mapping for the kernel text */
-    result = set_up_temporary_text_mapping(pgd);
+    /*
+     * The new mapping only has to cover the page containing the image
+     * kernel's entry point (jump_address_phys), because the switch over to
+     * it is carried out by relocated code running from a page allocated
+     * specifically for this purpose and covered by the identity mapping, so
+     * the temporary kernel text mapping is only needed for the final jump.
+     * Moreover, in that mapping the virtual address of the image kernel's
+     * entry point must be the same as its virtual address in the image
+     * kernel (restore_jump_address), so the image kernel's
+     * restore_registers() code doesn't find itself in a different area of
+     * the virtual address space after switching over to the original page
+     * tables used by the image kernel.
+     */
+    info.offset = restore_jump_address - jump_address_phys;
+    result = kernel_ident_mapping_init(&info, pgd, jump_address_phys,
+                       jump_address_phys + PMD_SIZE);
     if (result)
         return result;

     /* Set up the direct mapping from scratch */
+    info.offset = __PAGE_OFFSET;
     for (i = 0; i < nr_pfn_mapped; i++) {
         mstart = pfn_mapped[i].start << PAGE_SHIFT;
         mend   = pfn_mapped[i].end << PAGE_SHIFT;