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Message-ID: <1771166.6Dy2cXd33p@vostro.rjw.lan>
Date: Tue, 02 Aug 2016 02:38:21 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>, Yinghai Lu <yinghai@...nel.org>, Pavel Machek <pavel@....cz>, x86@...nel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v1 2/2] x86/power/64: Fix __PAGE_OFFSET usage on restore
On Monday, August 01, 2016 10:08:00 AM Thomas Garnier wrote:
> When KASLR memory randomization is used, __PAGE_OFFSET is a global
> variable changed during boot. The assembly code was using the variable
> as an immediate value to calculate the cr3 physical address. The
> physical address was incorrect resulting to a GP fault.
>
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> ---
> arch/x86/power/hibernate_asm_64.S | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/power/hibernate_asm_64.S b/arch/x86/power/hibernate_asm_64.S
> index 8eee0e9..8db4905 100644
> --- a/arch/x86/power/hibernate_asm_64.S
> +++ b/arch/x86/power/hibernate_asm_64.S
> @@ -23,6 +23,16 @@
> #include <asm/processor-flags.h>
> #include <asm/frame.h>
>
> +/*
> + * A global variable holds the page_offset when KASLR memory randomization
> + * is enabled.
> + */
> +#ifdef CONFIG_RANDOMIZE_MEMORY
> +#define __PAGE_OFFSET_REF __PAGE_OFFSET
> +#else
> +#define __PAGE_OFFSET_REF $__PAGE_OFFSET
> +#endif
> +
> ENTRY(swsusp_arch_suspend)
> movq $saved_context, %rax
> movq %rsp, pt_regs_sp(%rax)
> @@ -72,7 +82,7 @@ ENTRY(restore_image)
> /* code below has been relocated to a safe page */
> ENTRY(core_restore_code)
> /* switch to temporary page tables */
> - movq $__PAGE_OFFSET, %rcx
> + movq __PAGE_OFFSET_REF, %rcx
> subq %rcx, %rax
> movq %rax, %cr3
> /* flush TLB */
>
I'm not particularly liking the #ifdefs and they won't be really
necessary if the subtraction is carried out by the C code IMO.
What about the patch below instead?
---
arch/x86/power/hibernate_64.c | 18 +++++++++---------
arch/x86/power/hibernate_asm_64.S | 2 --
2 files changed, 9 insertions(+), 11 deletions(-)
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
@@ -72,8 +72,6 @@ ENTRY(restore_image)
/* 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
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
@@ -37,11 +37,11 @@ unsigned long jump_address_phys;
*/
unsigned long restore_cr3 __visible;
-pgd_t *temp_level4_pgt __visible;
+unsigned long temp_level4_pgt __visible;
unsigned long relocated_restore_code __visible;
-static int set_up_temporary_text_mapping(void)
+static int set_up_temporary_text_mapping(pgd_t *pgd)
{
pmd_t *pmd;
pud_t *pud;
@@ -71,7 +71,7 @@ static int set_up_temporary_text_mapping
__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),
+ set_pgd(pgd + pgd_index(restore_jump_address),
__pgd(__pa(pud) | _KERNPG_TABLE));
return 0;
@@ -90,15 +90,16 @@ static int set_up_temporary_mappings(voi
.kernel_mapping = true,
};
unsigned long mstart, mend;
+ pgd_t *pgd;
int result;
int i;
- temp_level4_pgt = (pgd_t *)get_safe_page(GFP_ATOMIC);
- if (!temp_level4_pgt)
+ pgd = (pgd_t *)get_safe_page(GFP_ATOMIC);
+ if (!pgd)
return -ENOMEM;
/* Prepare a temporary mapping for the kernel text */
- result = set_up_temporary_text_mapping();
+ result = set_up_temporary_text_mapping(pgd);
if (result)
return result;
@@ -107,13 +108,12 @@ static int set_up_temporary_mappings(voi
mstart = pfn_mapped[i].start << PAGE_SHIFT;
mend = pfn_mapped[i].end << PAGE_SHIFT;
- result = kernel_ident_mapping_init(&info, temp_level4_pgt,
- mstart, mend);
-
+ result = kernel_ident_mapping_init(&info, pgd, mstart, mend);
if (result)
return result;
}
+ temp_level4_pgt = (unsigned long)pgd - __PAGE_OFFSET;
return 0;
}
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