Message-ID: <3006711.q9ei2E2zzf@vostro.rjw.lan>
Date:	Mon, 13 Jun 2016 15:42:26 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Ingo Molnar <mingo@...nel.org>,
	Logan Gunthorpe <logang@...tatee.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: [PATCH] x86 / hibernate: Fix 64-bit code passing control to image kernel

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Logan Gunthorpe reports that hibernation stopped working reliably for
him after commit ab76f7b4ab23 (x86/mm: Set NX on gap between __ex_table
and rodata).  Most likely, what happens is that the page containing
the image kernel's entry point is sometimes marked as non-executable
in the page tables used at the time of the final jump to the image
kernel.  That at least is why commit ab76f7b4ab23 may matter.

However, there is one more long-standing issue with the code in
question, which is that the temporary page tables set up by it
to avoid page tables corruption when the last bits of the image
kernel's memory contents are copied into their original page frames
re-use the boot kernel's text mapping, but that mapping may very
well get corrupted just like any other part of the page tables.
Of course, if that happens, the final jump to the image kernel's
entry point will go to nowhere.

As it turns out, those two issues may be addressed simultaneously.

To that end, note that the code copying the last bits of the image
kernel's memory contents to the page frames occupied by them
previoulsy doesn't use the kernel text mapping, because it runs from
a special page covered by the identity mapping set up for that code
from scratch.  Hence, the kernel text mapping is only needed before
that code starts to run and then it will only be used just for the
final jump to the image kernel's entry point.

Accordingly, the temporary page tables set up in swsusp_arch_resume()
on x86-64 can re-use the boot kernel's text mapping to start with,
but after all of the image kernel's memory contents are in place,
that mapping has to be replaced with a new one that will allow the
final jump to the image kernel's entry point to succeed.  Of course,
since the first thing the image kernel does after getting control back
is to switch over to its own original page tables, the new kernel text
mapping only has to cover the image kernel's entry point (along with
some following bytes).  Moreover, it has to do that so the virtual
address of the image kernel's entry point before the jump is the same
as the one mapped by the image kernel's page tables.

With that in mind, modify the x86-64's arch_hibernation_header_save()
and arch_hibernation_header_restore() routines to pass the physical
address of the image kernel's entry point (in addition to its virtual
address) to the boot kernel (a small piece of assembly code involved
in passing the entry point's virtual address to the image kernel is
not necessary any more after that, so drop it).  Update RESTORE_MAGIC
too to reflect the image header format change.

Next, in set_up_temporary_mappings(), use the physical and virtual
addresses of the image kernel's entry point passed in the image
header to set up a minimum kernel text mapping (using memory pages
that won't be overwritten by the image kernel's memory contents) that
will map those addresses to each other as appropriate.  Do not use
that mapping immediately, though.  Instead, use the original boot
kernel text mapping to start with and switch over to the new one
after all of the image kernel's memory has been restored, right
before the final jump to the image kernel's entry point.

This makes the concern about the possible corruption of the original
boot kernel text mapping go away and if the the minimum kernel text
mapping used for the final jump marks the image kernel's entry point
memory as executable, the jump to it is guaraneed to succeed.

Fixes: ab76f7b4ab23 (x86/mm: Set NX on gap between __ex_table and rodata)
Link: http://marc.info/?l=linux-pm&m=146372852823760&w=2
Reported-by: Logan Gunthorpe <logang@...tatee.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 arch/x86/power/hibernate_64.c     |   66 +++++++++++++++++++++++++++++++++++---
 arch/x86/power/hibernate_asm_64.S |   31 +++++++++--------
 2 files changed, 77 insertions(+), 20 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
@@ -27,7 +27,8 @@ extern asmlinkage __visible int restore_
  * 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 __visible;
+void *restore_jump_address __visible;
+unsigned long jump_address_phys;
 
 /*
  * Value of the cr3 register from before the hibernation (this value is passed
@@ -37,8 +38,51 @@ unsigned long restore_cr3 __visible;
 
 pgd_t *temp_level4_pgt __visible;
 
+void *restore_pgd_addr __visible;
+pgd_t restore_pgd __visible;
+
 void *relocated_restore_code __visible;
 
+static int prepare_temporary_text_mapping(void)
+{
+	unsigned long vaddr = (unsigned long)restore_jump_address;
+	unsigned long paddr = jump_address_phys & PMD_MASK;
+	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.
+	 * However, 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;
+
+	restore_pgd = __pgd(__pa(pud) | _KERNPG_TABLE);
+
+	pud += pud_index(vaddr);
+	pmd = (pmd_t *)get_safe_page(GFP_ATOMIC);
+	if (!pmd)
+		return -ENOMEM;
+
+	set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
+
+	pmd += pmd_index(vaddr);
+	set_pmd(pmd, __pmd(paddr | __PAGE_KERNEL_LARGE_EXEC));
+
+	restore_pgd_addr = temp_level4_pgt + pgd_index(vaddr);
+	return 0;
+}
+
 static void *alloc_pgt_page(void *context)
 {
 	return (void *)get_safe_page(GFP_ATOMIC);
@@ -59,10 +103,19 @@ static int set_up_temporary_mappings(voi
 	if (!temp_level4_pgt)
 		return -ENOMEM;
 
-	/* It is safe to reuse the original kernel mapping */
+	/* Re-use the original kernel text mapping for now */
 	set_pgd(temp_level4_pgt + pgd_index(__START_KERNEL_map),
 		init_level4_pgt[pgd_index(__START_KERNEL_map)]);
 
+	/*
+	 * Prepare a temporary mapping for the kernel text, but don't use it
+	 * just yet, we'll switch over to it later.  It only has to cover one
+	 * piece of code: the page containing the image kernel's entry point.
+	 */
+	result = prepare_temporary_text_mapping();
+	if (result)
+		return result;
+
 	/* Set up the direct mapping from scratch */
 	for (i = 0; i < nr_pfn_mapped; i++) {
 		mstart = pfn_mapped[i].start << PAGE_SHIFT;
@@ -108,12 +161,13 @@ int pfn_is_nosave(unsigned long pfn)
 }
 
 struct restore_data_record {
-	unsigned long jump_address;
+	void *jump_address;
+	unsigned long jump_address_phys;
 	unsigned long cr3;
 	unsigned long magic;
 };
 
-#define RESTORE_MAGIC	0x0123456789ABCDEFUL
+#define RESTORE_MAGIC	0x123456789ABCDEF0UL
 
 /**
  *	arch_hibernation_header_save - populate the architecture specific part
@@ -126,7 +180,8 @@ int arch_hibernation_header_save(void *a
 
 	if (max_size < sizeof(struct restore_data_record))
 		return -EOVERFLOW;
-	rdr->jump_address = restore_jump_address;
+	rdr->jump_address = &restore_registers;
+	rdr->jump_address_phys = __pa_symbol(&restore_registers);
 	rdr->cr3 = restore_cr3;
 	rdr->magic = RESTORE_MAGIC;
 	return 0;
@@ -142,6 +197,7 @@ int arch_hibernation_header_restore(void
 	struct restore_data_record *rdr = addr;
 
 	restore_jump_address = rdr->jump_address;
+	jump_address_phys = rdr->jump_address_phys;
 	restore_cr3 = rdr->cr3;
 	return (rdr->magic == RESTORE_MAGIC) ? 0 : -EINVAL;
 }
Index: linux-pm/arch/x86/power/hibernate_asm_64.S
===================================================================
--- linux-pm.orig/arch/x86/power/hibernate_asm_64.S
+++ linux-pm/arch/x86/power/hibernate_asm_64.S
@@ -44,9 +44,6 @@ ENTRY(swsusp_arch_suspend)
 	pushfq
 	popq	pt_regs_flags(%rax)
 
-	/* save the address of restore_registers */
-	movq	$restore_registers, %rax
-	movq	%rax, restore_jump_address(%rip)
 	/* save cr3 */
 	movq	%cr3, %rax
 	movq	%rax, restore_cr3(%rip)
@@ -72,8 +69,10 @@ ENTRY(restore_image)
 	movq	%rax, %cr4;  # turn PGE back on
 
 	/* prepare to jump to the image kernel */
-	movq	restore_jump_address(%rip), %rax
 	movq	restore_cr3(%rip), %rbx
+	movq	restore_jump_address(%rip), %r10
+	movq	restore_pgd(%rip), %r8
+	movq	restore_pgd_addr(%rip), %r9
 
 	/* prepare to copy image data to their original locations */
 	movq	restore_pblist(%rip), %rdx
@@ -96,20 +95,22 @@ ENTRY(core_restore_code)
 	/* progress to the next pbe */
 	movq	pbe_next(%rdx), %rdx
 	jmp	.Lloop
+
 .Ldone:
+	/* switch over to the temporary kernel text mapping */
+	movq	%r8, (%r9)
+	/* flush TLB */
+	movq	%rax, %rdx
+	andq	$~(X86_CR4_PGE), %rdx
+	movq	%rdx, %cr4;  # turn off PGE
+	movq	%cr3, %rcx;  # flush TLB
+	movq	%rcx, %cr3;
+	movq	%rax, %cr4;  # turn PGE back on
 	/* jump to the restore_registers address from the image header */
-	jmpq	*%rax
-	/*
-	 * NOTE: This assumes that the boot kernel's text mapping covers the
-	 * image kernel's page containing restore_registers and the address of
-	 * this page is the same as in the image kernel's text mapping (it
-	 * should always be true, because the text mapping is linear, starting
-	 * from 0, and is supposed to cover the entire kernel text for every
-	 * kernel).
-	 *
-	 * code below belongs to the image kernel
-	 */
+	jmpq	*%r10
 
+	 /* code below belongs to the image kernel */
+	.align PAGE_SIZE
 ENTRY(restore_registers)
 	FRAME_BEGIN
 	/* go back to the original page tables */

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