x86/power/64: Fix kernel text mapping corruption during image restoration

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

BugLink: https://bugs.launchpad.net/bugs/1616781

Logan Gunthorpe reports that hibernation stopped working reliably for
him after commit ab76f7b4ab23 (x86/mm: Set NX on gap between __ex_table
and rodata).

That turns out to be a consequence of a long-standing issue with the
64-bit image restoration code on x86, 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.

The exact reason why commit ab76f7b4ab23 matters here is that it
sometimes causes a PMD of a large page to be split into PTEs
that are allocated dynamically and get corrupted during image
restoration as described above.

To fix that issue 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 need to contain the kernel text mapping too.  That mapping
is only going to be used for the final jump to the image kernel, so
it only needs to cover the image kernel's entry point, because the
first thing the image kernel does after getting control back is to
switch over to its own original page tables.  Moreover, the virtual
address of the image kernel's entry point in that mapping has to be
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.

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@deltatee.com>
Reported-and-tested-by: Borislav Petkov <bp@suse.de>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit 65c0554b73c920023cc8998802e508b798113b46)
Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
---
 arch/x86/power/hibernate_64.c     | 97 ++++++++++++++++++++++++++++++++++-----
 arch/x86/power/hibernate_asm_64.S | 55 ++++++++++------------
 2 files changed, 109 insertions(+), 43 deletions(-)

On 25/08/16 09:44, AceLan Kao wrote:
> From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1616781
> 
> Logan Gunthorpe reports that hibernation stopped working reliably for
> him after commit ab76f7b4ab23 (x86/mm: Set NX on gap between __ex_table
> and rodata).
> 
> That turns out to be a consequence of a long-standing issue with the
> 64-bit image restoration code on x86, 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.
> 
> The exact reason why commit ab76f7b4ab23 matters here is that it
> sometimes causes a PMD of a large page to be split into PTEs
> that are allocated dynamically and get corrupted during image
> restoration as described above.
> 
> To fix that issue 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 need to contain the kernel text mapping too.  That mapping
> is only going to be used for the final jump to the image kernel, so
> it only needs to cover the image kernel's entry point, because the
> first thing the image kernel does after getting control back is to
> switch over to its own original page tables.  Moreover, the virtual
> address of the image kernel's entry point in that mapping has to be
> 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.
> 
> 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@deltatee.com>
> Reported-and-tested-by: Borislav Petkov <bp@suse.de>
> Tested-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> (cherry picked from commit 65c0554b73c920023cc8998802e508b798113b46)
> Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
> ---
>  arch/x86/power/hibernate_64.c     | 97 ++++++++++++++++++++++++++++++++++-----
>  arch/x86/power/hibernate_asm_64.S | 55 ++++++++++------------
>  2 files changed, 109 insertions(+), 43 deletions(-)
> 
> diff --git a/arch/x86/power/hibernate_64.c b/arch/x86/power/hibernate_64.c
> index 009947d..f2b5e6a 100644
> --- a/arch/x86/power/hibernate_64.c
> +++ b/arch/x86/power/hibernate_64.c
> @@ -19,6 +19,7 @@
>  #include <asm/mtrr.h>
>  #include <asm/sections.h>
>  #include <asm/suspend.h>
> +#include <asm/tlbflush.h>
>  
>  /* Defined in hibernate_asm_64.S */
>  extern asmlinkage __visible int restore_image(void);
> @@ -28,6 +29,7 @@ extern asmlinkage __visible int restore_image(void);
>   * kernel's text (this value is passed in the image header).
>   */
>  unsigned long restore_jump_address __visible;
> +unsigned long jump_address_phys;
>  
>  /*
>   * Value of the cr3 register from before the hibernation (this value is passed
> @@ -37,7 +39,43 @@ unsigned long restore_cr3 __visible;
>  
>  pgd_t *temp_level4_pgt __visible;
>  
> -void *relocated_restore_code __visible;
> +unsigned long relocated_restore_code __visible;
> +
> +static int set_up_temporary_text_mapping(void)
> +{
> +	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(temp_level4_pgt + pgd_index(restore_jump_address),
> +		__pgd(__pa(pud) | _KERNPG_TABLE));
> +
> +	return 0;
> +}
>  
>  static void *alloc_pgt_page(void *context)
>  {
> @@ -59,9 +97,10 @@ static int set_up_temporary_mappings(void)
>  	if (!temp_level4_pgt)
>  		return -ENOMEM;
>  
> -	/* It is safe to reuse the original kernel mapping */
> -	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 */
> +	result = set_up_temporary_text_mapping();
> +	if (result)
> +		return result;
>  
>  	/* Set up the direct mapping from scratch */
>  	for (i = 0; i < nr_pfn_mapped; i++) {
> @@ -78,19 +117,50 @@ static int set_up_temporary_mappings(void)
>  	return 0;
>  }
>  
> +static int relocate_restore_code(void)
> +{
> +	pgd_t *pgd;
> +	pud_t *pud;
> +
> +	relocated_restore_code = get_safe_page(GFP_ATOMIC);
> +	if (!relocated_restore_code)
> +		return -ENOMEM;
> +
> +	memcpy((void *)relocated_restore_code, &core_restore_code, PAGE_SIZE);
> +
> +	/* Make the page containing the relocated code executable */
> +	pgd = (pgd_t *)__va(read_cr3()) + pgd_index(relocated_restore_code);
> +	pud = pud_offset(pgd, relocated_restore_code);
> +	if (pud_large(*pud)) {
> +		set_pud(pud, __pud(pud_val(*pud) & ~_PAGE_NX));
> +	} else {
> +		pmd_t *pmd = pmd_offset(pud, relocated_restore_code);
> +
> +		if (pmd_large(*pmd)) {
> +			set_pmd(pmd, __pmd(pmd_val(*pmd) & ~_PAGE_NX));
> +		} else {
> +			pte_t *pte = pte_offset_kernel(pmd, relocated_restore_code);
> +
> +			set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_NX));
> +		}
> +	}
> +	__flush_tlb_all();
> +
> +	return 0;
> +}
> +
>  int swsusp_arch_resume(void)
>  {
>  	int error;
>  
>  	/* We have got enough memory and from now on we cannot recover */
> -	if ((error = set_up_temporary_mappings()))
> +	error = set_up_temporary_mappings();
> +	if (error)
>  		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);
> +	error = relocate_restore_code();
> +	if (error)
> +		return error;
>  
>  	restore_image();
>  	return 0;
> @@ -109,11 +179,12 @@ int pfn_is_nosave(unsigned long pfn)
>  
>  struct restore_data_record {
>  	unsigned long 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 +197,8 @@ int arch_hibernation_header_save(void *addr, unsigned int max_size)
>  
>  	if (max_size < sizeof(struct restore_data_record))
>  		return -EOVERFLOW;
> -	rdr->jump_address = restore_jump_address;
> +	rdr->jump_address = (unsigned long)&restore_registers;
> +	rdr->jump_address_phys = __pa_symbol(&restore_registers);
>  	rdr->cr3 = restore_cr3;
>  	rdr->magic = RESTORE_MAGIC;
>  	return 0;
> @@ -142,6 +214,7 @@ int arch_hibernation_header_restore(void *addr)
>  	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;
>  }
> diff --git a/arch/x86/power/hibernate_asm_64.S b/arch/x86/power/hibernate_asm_64.S
> index e2386cb..7ffbb18 100644
> --- a/arch/x86/power/hibernate_asm_64.S
> +++ b/arch/x86/power/hibernate_asm_64.S
> @@ -42,9 +42,6 @@ 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)
> @@ -53,31 +50,34 @@ ENTRY(swsusp_arch_suspend)
>  	ret
>  
>  ENTRY(restore_image)
> -	/* switch to temporary page tables */
> -	movq	$__PAGE_OFFSET, %rdx
> -	movq	temp_level4_pgt(%rip), %rax
> -	subq	%rdx, %rax
> -	movq	%rax, %cr3
> -	/* Flush TLB */
> -	movq	mmu_cr4_features(%rip), %rax
> -	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
> -
>  	/* prepare to jump to the image kernel */
> -	movq	restore_jump_address(%rip), %rax
> -	movq	restore_cr3(%rip), %rbx
> +	movq	restore_jump_address(%rip), %r8
> +	movq	restore_cr3(%rip), %r9
> +
> +	/* prepare to switch to temporary page tables */
> +	movq	temp_level4_pgt(%rip), %rax
> +	movq	mmu_cr4_features(%rip), %rbx
>  
>  	/* prepare to copy image data to their original locations */
>  	movq	restore_pblist(%rip), %rdx
> +
> +	/* jump to relocated restore code */
>  	movq	relocated_restore_code(%rip), %rcx
>  	jmpq	*%rcx
>  
>  	/* code below has been relocated to a safe page */
>  ENTRY(core_restore_code)
> +	/* switch to temporary page tables */
> +	movq	$__PAGE_OFFSET, %rcx
> +	subq	%rcx, %rax
> +	movq	%rax, %cr3
> +	/* flush TLB */
> +	movq	%rbx, %rcx
> +	andq	$~(X86_CR4_PGE), %rcx
> +	movq	%rcx, %cr4;  # turn off PGE
> +	movq	%cr3, %rcx;  # flush TLB
> +	movq	%rcx, %cr3;
> +	movq	%rbx, %cr4;  # turn PGE back on
>  .Lloop:
>  	testq	%rdx, %rdx
>  	jz	.Ldone
> @@ -92,23 +92,16 @@ ENTRY(core_restore_code)
>  	/* progress to the next pbe */
>  	movq	pbe_next(%rdx), %rdx
>  	jmp	.Lloop
> +
>  .Ldone:
>  	/* 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	*%r8
>  
> +	 /* code below belongs to the image kernel */
> +	.align PAGE_SIZE
>  ENTRY(restore_registers)
>  	/* go back to the original page tables */
> -	movq    %rbx, %cr3
> +	movq    %r9, %cr3
>  
>  	/* Flush TLB, including "global" things (vmalloc) */
>  	movq	mmu_cr4_features(%rip), %rax
> 

Although this is quite a scary looking change, it has been tested by
several trusted upstream folk and it's an upstream cherry pick that
seems to fix a long standing issue, so I'm happy to ack it.

Acked-by: Colin Ian King <colin.king@canonical.com>

A hairy looking patch, but authored and tested by well known devs. Not
much for test results though. I am also wondering why this isn't Cc stable.