Hibernation: Arbitrary boot kernel support on x86_64

Make it possible to restore a hibernation image on x86_64 with the help of a
kernel different from the one in the image.

The idea is to split the core restoration code into two separate parts and to
place each of them in a different page.   The first part belongs to the boot
kernel and is executed as the last step of the image kernel's memory
restoration procedure.   Before being executed, it is relocated to a safe page
that won't be overwritten while copying the image kernel pages.

The final operation performed by it is a jump to the second part of the core
restoration code that belongs to the image kernel and has just been restored.
This code makes the CPU switch to the image kernel's page tables and restores
the state of general purpose registers (including the stack pointer) from
before the hibernation.

The main issue with this idea is that in order to jump to the second part of
the core restoration code the boot kernel needs to know its address.
 However, this address may be passed to it in the image header.   Namely, the
part of the image header previously used for checking if the version of the
image kernel is correct can be replaced with some architecture specific data
that will allow the boot kernel to jump to the right address within the image
kernel.   These data should also be used for checking if the image kernel is
compatible with the boot kernel (as far as the memory restroration procedure
is concerned).  It can be done, for example, with the help of a "magic" value
that has to be equal in both kernels, so that they can be regarded as
compatible.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 53 insertions, 1 deletions

diff --git a/arch/x86/kernel/suspend_64.c b/arch/x86/kernel/suspend_64.c
index 573c0a6e0ac6..01fbfb018ca9 100644
--- a/arch/x86/kernel/suspend_64.c
+++ b/arch/x86/kernel/suspend_64.c
@@ -150,8 +150,16 @@ void fix_processor_context(void)
 /* Defined in arch/x86_64/kernel/suspend_asm.S */
 extern int restore_image(void);
 
+/*
+ * Address to jump to in the last phase of restore in order to get to the image
+ * kernel's text (this value is passed in the image header).
+ */
+unsigned long restore_jump_address;
+
 pgd_t *temp_level4_pgt;
 
+void *relocated_restore_code;
+
 static int res_phys_pud_init(pud_t *pud, unsigned long address, unsigned long end)
 {
         long i, j;
@@ -175,7 +183,7 @@ static int res_phys_pud_init(pud_t *pud, unsigned long address, unsigned long en
 
                         if (paddr >= end)
                                 break;
-                        pe = _PAGE_NX | _PAGE_PSE | _KERNPG_TABLE | paddr;
+                        pe = __PAGE_KERNEL_LARGE_EXEC | paddr;
                         pe &= __supported_pte_mask;
                         set_pmd(pmd, __pmd(pe));
                 }
@@ -222,6 +230,13 @@ int swsusp_arch_resume(void)
         /* We have got enough memory and from now on we cannot recover */
         if ((error = set_up_temporary_mappings()))
                 return error;
+
+        relocated_restore_code = (void *)get_safe_page(GFP_ATOMIC);
+        if (!relocated_restore_code)
+                return -ENOMEM;
+        memcpy(relocated_restore_code, &core_restore_code,
+               &restore_registers - &core_restore_code);
+
         restore_image();
         return 0;
 }
@@ -236,4 +251,41 @@ int pfn_is_nosave(unsigned long pfn)
         unsigned long nosave_end_pfn = PAGE_ALIGN(__pa_symbol(&__nosave_end)) >> PAGE_SHIFT;
         return (pfn >= nosave_begin_pfn) && (pfn < nosave_end_pfn);
 }
+
+struct restore_data_record {
+        unsigned long jump_address;
+        unsigned long control;
+};
+
+#define RESTORE_MAGIC   0x0123456789ABCDEFUL
+
+/**
+ *      arch_hibernation_header_save - populate the architecture specific part
+ *              of a hibernation image header
+ *      @addr: address to save the data at
+ */
+int arch_hibernation_header_save(void *addr, unsigned int max_size)
+{
+        struct restore_data_record *rdr = addr;
+
+        if (max_size < sizeof(struct restore_data_record))
+                return -EOVERFLOW;
+        rdr->jump_address = restore_jump_address;
+        rdr->control = (restore_jump_address ^ RESTORE_MAGIC);
+        return 0;
+}
+
+/**
+ *      arch_hibernation_header_restore - read the architecture specific data
+ *              from the hibernation image header
+ *      @addr: address to read the data from
+ */
+int arch_hibernation_header_restore(void *addr)
+{
+        struct restore_data_record *rdr = addr;
+
+        restore_jump_address = rdr->jump_address;
+        return (rdr->control == (restore_jump_address ^ RESTORE_MAGIC)) ?
+                        0 : -EINVAL;
+}
 #endif /* CONFIG_HIBERNATION */