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Date: Wed, 10 Aug 2016 02:21:18 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Jiri Kosina <jikos@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Thomas Garnier <thgarnie@...gle.com>, Linux PM list <linux-pm@...r.kernel.org>, the arch/x86 maintainers <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Yinghai Lu <yinghai@...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>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Borislav Petkov <bpetkov@...e.de>
Subject: Re: [Resend][PATCH] x86/power/64: Always create temporary identity mapping correctly
On Tuesday, August 09, 2016 11:23:31 PM Rafael J. Wysocki wrote:
> On Tue, Aug 9, 2016 at 10:02 PM, Jiri Kosina <jikos@...nel.org> wrote:
> > On Tue, 9 Aug 2016, Rafael J. Wysocki wrote:
> >
> >> I have a murky suspicion, but it is really weird. Namely, what if
> >> restore_jump_address in set_up_temporary_text_mapping() happens to be
> >> covered by the restore kernel's identity mapping? Then, the image
> >> kernel's entry point may get overwritten by something else in
> >> core_restore_code().
> >
> > So this made me to actually test a scenario where I'd suspend a kernel
> > that's known-broken (i.e. contains 021182e52fe), and then have it resumed
> > by a kernel that has 021182e52fe reverted. It resumed successfully.
> >
> > Just a datapoint.
>
> That indicates the problem is somewhere in the restore kernel and no
> surprises there.
>
> I am able to reproduce the original problem (a triple fault on resume
> with CONFIG_RANDOMIZE_MEMORY set) without the $subject patch, but the
> patch fixes it for me.
>
> Question is why it is not sufficient for you and Boris and the above
> theory is about the only one I can come up with ATM.
>
> I'm going to compare the configs etc, but I guess I just end up
> writing a patch to test that theory unless someone has any other idea
> in the meantime.
For the lack of better ideas, below is a patch to try.
It avoids the possible issue with the restore kernel's identity mapping overlap
with restore_jump_address by creating special super-simple page tables just
for the final jump to the image kernel.
It is on top of the $subject patch. My test box still works with this applied,
but then it worked without it as well.
If it doesn't help, the identity mapping created by set_up_temporary_mappings()
is still not adequate for some reason most likely and we'll need to find out
why.
Thanks,
Rafael
---
arch/x86/power/hibernate_64.c | 40 +++++++++++++++++++++++++++++++-------
arch/x86/power/hibernate_asm_64.S | 10 +++++++++
2 files changed, 43 insertions(+), 7 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
@@ -38,14 +38,20 @@ unsigned long jump_address_phys;
unsigned long restore_cr3 __visible;
unsigned long temp_level4_pgt __visible;
+unsigned long jump_level4_pgt __visible;
unsigned long relocated_restore_code __visible;
-static int set_up_temporary_text_mapping(pgd_t *pgd)
+static int set_up_temporary_text_mapping(void)
{
+ pgd_t *pgd;
pmd_t *pmd;
pud_t *pud;
+ pgd = (pgd_t *)get_safe_page(GFP_ATOMIC);
+ if (!pgd)
+ return -ENOMEM;
+
/*
* The new mapping only has to cover the page containing the image
* kernel's entry point (jump_address_phys), because the switch over to
@@ -74,6 +80,23 @@ static int set_up_temporary_text_mapping
set_pgd(pgd + pgd_index(restore_jump_address),
__pgd(__pa(pud) | _KERNPG_TABLE));
+ 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(relocated_restore_code),
+ __pmd((__pa(relocated_restore_code) & PMD_MASK) | __PAGE_KERNEL_LARGE_EXEC));
+ set_pud(pud + pud_index(relocated_restore_code),
+ __pud(__pa(pmd) | _KERNPG_TABLE));
+ set_pgd(pgd + pgd_index(relocated_restore_code),
+ __pgd(__pa(pud) | _KERNPG_TABLE));
+
+ jump_level4_pgt = __pa(pgd);
+
return 0;
}
@@ -98,11 +121,6 @@ static int set_up_temporary_mappings(voi
if (!pgd)
return -ENOMEM;
- /* Prepare a temporary mapping for the kernel text */
- result = set_up_temporary_text_mapping(pgd);
- 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;
@@ -122,7 +140,10 @@ static int relocate_restore_code(void)
pgd_t *pgd;
pud_t *pud;
- relocated_restore_code = get_safe_page(GFP_ATOMIC);
+ do
+ relocated_restore_code = get_safe_page(GFP_ATOMIC);
+ while ((relocated_restore_code & PMD_MASK) == (restore_jump_address & PMD_MASK));
+
if (!relocated_restore_code)
return -ENOMEM;
@@ -162,6 +183,11 @@ int swsusp_arch_resume(void)
if (error)
return error;
+ /* Prepare a temporary mapping for the jump to the image kernel */
+ error = set_up_temporary_text_mapping();
+ if (error)
+ return error;
+
restore_image();
return 0;
}
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
@@ -57,6 +57,7 @@ ENTRY(restore_image)
/* prepare to jump to the image kernel */
movq restore_jump_address(%rip), %r8
movq restore_cr3(%rip), %r9
+ movq jump_level4_pgt(%rip), %r10
/* prepare to switch to temporary page tables */
movq temp_level4_pgt(%rip), %rax
@@ -96,6 +97,15 @@ ENTRY(core_restore_code)
jmp .Lloop
.Ldone:
+ /* switch to jump page tables */
+ movq %r10, %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
/* jump to the restore_registers address from the image header */
jmpq *%r8
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