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Date: Wed, 29 Jun 2016 07:48:03 -0700
From: Kees Cook <keescook@...omium.org>
To: Logan Gunthorpe <logang@...tatee.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Borislav Petkov <bp@...en8.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
lkml <linux-kernel@...r.kernel.org>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Andy Lutomirski <luto@...nel.org>,
Brian Gerst <brgerst@...il.com>,
Denys Vlasenko <dvlasenk@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
Linux PM list <linux-pm@...r.kernel.org>,
Stephen Smalley <sds@...ho.nsa.gov>
Subject: Re: [PATCH v3] x86/power/64: Fix kernel text mapping corruption
during image restoration
On Mon, Jun 27, 2016 at 4:33 PM, Logan Gunthorpe <logang@...tatee.com> wrote:
> Hey,
>
> This version is working for me as well. Thanks.
>
> Logan
>
> On 27/06/16 08:24 AM, Rafael J. Wysocki wrote:
>>
>> On Tuesday, June 21, 2016 11:04:41 AM Kees Cook wrote:
>>>
>>> On Mon, Jun 20, 2016 at 9:35 PM, Logan Gunthorpe <logang@...tatee.com>
>>> wrote:
>>>>
>>>> Hey Rafael,
>>>>
>>>> This patch appears to be working on my laptop. Thanks.
>>>
>>>
>>> Same for me: resume still works with KASLR in my tests too.
>>
>>
>> Unfortunately, Boris still sees post-resume memory corruption with the
>> patch
>> you have tested, but that turns out to be a result of some super-weird
>> corruption of a pointer on the stack which leads to a store at a wrong
>> address
>> (and there's no way it can be related to the rest of the patch).
>>
>> We have verified that it can be avoided by rearranging
>> set_up_temporary_text_mapping()
>> to use fewer local variables and the appended patch contains this
>> modification.
>>
>> I also went on and changed relocate_restore_code() slightly in a similar
>> fashion,
>> but all of those changes should not affect the behavior (unless there's
>> something
>> insane going on behind the curtains, that is).
>>
>> Kees, Logan, Boris, please try this one and let me know if it works for
>> you.
Tested-by: Kees Cook <keescook@...omium.org>
I've done a few KASLR boots, and everything continues to look good to
me. Thanks!
-Kees
>>
>> Thanks,
>> Rafael
>>
>>
>> ---
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> Subject: [PATCH v2] x86/power/64: Fix kernel text mapping corruption
>> during image restoration
>>
>> 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@...tatee.com>
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> ---
>> arch/x86/power/hibernate_64.c | 90
>> ++++++++++++++++++++++++++++++++------
>> arch/x86/power/hibernate_asm_64.S | 55 ++++++++++-------------
>> 2 files changed, 102 insertions(+), 43 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
>> @@ -28,6 +28,7 @@ extern asmlinkage __visible int restore_
>> * 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 +38,43 @@ 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 +96,10 @@ static int set_up_temporary_mappings(voi
>> 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 +116,44 @@ static int set_up_temporary_mappings(voi
>> return 0;
>> }
>>
>> +static int relocate_restore_code(void)
>> +{
>> + pgd_t *pgd;
>> + pmd_t *pmd;
>> +
>> + 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);
>> + pmd = pmd_offset(pud_offset(pgd, relocated_restore_code),
>> + 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));
>> + }
>> +
>> + 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 +172,12 @@ 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 +190,8 @@ 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 = (unsigned long)&restore_registers;
>> + rdr->jump_address_phys = __pa_symbol(&restore_registers);
>> rdr->cr3 = restore_cr3;
>> rdr->magic = RESTORE_MAGIC;
>> return 0;
>> @@ -142,6 +207,7 @@ 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)
>> @@ -57,31 +54,34 @@ ENTRY(swsusp_arch_suspend)
>> ENDPROC(swsusp_arch_suspend)
>>
>> 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
>> @@ -96,24 +96,17 @@ 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)
>> FRAME_BEGIN
>> /* 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
>>
>
--
Kees Cook
Chrome OS & Brillo Security
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