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* [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section
@ 2019-05-08  8:04 Baoquan He
  2019-05-08  8:24 ` Baoquan He
  0 siblings, 1 reply; 6+ messages in thread
From: Baoquan He @ 2019-05-08  8:04 UTC (permalink / raw)
  To: linux-kernel
  Cc: x86, tglx, mingo, bp, hpa, kirill.shutemov, keescook, Baoquan He

kernel_randomize_memory() hardcodes the size of vmemmap section as 1 TB,
to support the maximum amount of system RAM in 4-level paging mode, 64 TB.

However, 1 TB is not enough for vmemmap in 5-level paging mode. Assuming
the size of struct page is 64 Bytes, to support 4 PB system RAM in 5-level,
64 TB of vmemmap area is needed. The wrong hardcoding may cause vmemmap
stamping into the following cpu_entry_area section, if KASLR puts vmemmap
very close to cpu_entry_area , and the actual area of vmemmap is much
bigger than 1 TB.

So here calculate the actual size of vmemmap region, then align up to 1 TB
boundary. In 4-level it's always 1 TB. In 5-level it's adjusted on demand.
The current code reserves 0.5 PB for vmemmap in 5-level. In this new way,
the left space can be saved to join randomization to increase the entropy.

Signed-off-by: Baoquan He <bhe@redhat.com>
Acked-by: Kirill A. Shutemov <kirill@linux.intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v3->v4:
  Fix the incorrect style of code comment;
  Add ack tags from Kirill and Kees.
v3 discussion is here:
  http://lkml.kernel.org/r/20190422091045.GB3584@localhost.localdomain

 arch/x86/mm/kaslr.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index dc3f058bdf9b..c0eedb85a92f 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_region {
 } kaslr_regions[] = {
 	{ &page_offset_base, 0 },
 	{ &vmalloc_base, 0 },
-	{ &vmemmap_base, 1 },
+	{ &vmemmap_base, 0 },
 };
 
 /* Get size in bytes used by the memory region */
@@ -78,6 +78,7 @@ void __init kernel_randomize_memory(void)
 	unsigned long rand, memory_tb;
 	struct rnd_state rand_state;
 	unsigned long remain_entropy;
+	unsigned long vmemmap_size;
 
 	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
 	vaddr = vaddr_start;
@@ -109,6 +110,14 @@ void __init kernel_randomize_memory(void)
 	if (memory_tb < kaslr_regions[0].size_tb)
 		kaslr_regions[0].size_tb = memory_tb;
 
+	/*
+	 * Calculate how many TB vmemmap region needs, and aligned to
+	 * 1TB boundary.
+	 */
+	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
+		sizeof(struct page);
+	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
+
 	/* Calculate entropy available between regions */
 	remain_entropy = vaddr_end - vaddr_start;
 	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
-- 
2.17.2


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section
  2019-05-08  8:04 [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section Baoquan He
@ 2019-05-08  8:24 ` Baoquan He
  2019-05-08  9:04   ` Borislav Petkov
  0 siblings, 1 reply; 6+ messages in thread
From: Baoquan He @ 2019-05-08  8:24 UTC (permalink / raw)
  To: linux-kernel, stable; +Cc: x86, tglx, mingo, bp, hpa, kirill.shutemov, keescook

On 05/08/19 at 04:04pm, Baoquan He wrote:
> kernel_randomize_memory() hardcodes the size of vmemmap section as 1 TB,
> to support the maximum amount of system RAM in 4-level paging mode, 64 TB.
> 
> However, 1 TB is not enough for vmemmap in 5-level paging mode. Assuming
> the size of struct page is 64 Bytes, to support 4 PB system RAM in 5-level,
> 64 TB of vmemmap area is needed. The wrong hardcoding may cause vmemmap
> stamping into the following cpu_entry_area section, if KASLR puts vmemmap
> very close to cpu_entry_area , and the actual area of vmemmap is much
> bigger than 1 TB.
> 
> So here calculate the actual size of vmemmap region, then align up to 1 TB
> boundary. In 4-level it's always 1 TB. In 5-level it's adjusted on demand.
> The current code reserves 0.5 PB for vmemmap in 5-level. In this new way,
> the left space can be saved to join randomization to increase the entropy.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> Acked-by: Kirill A. Shutemov <kirill@linux.intel.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>

I think this's worth noticing stable tree:

Cc: stable@vger.kernel.org

> ---
> v3->v4:
>   Fix the incorrect style of code comment;
>   Add ack tags from Kirill and Kees.
> v3 discussion is here:
>   http://lkml.kernel.org/r/20190422091045.GB3584@localhost.localdomain
> 
>  arch/x86/mm/kaslr.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index dc3f058bdf9b..c0eedb85a92f 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_region {
>  } kaslr_regions[] = {
>  	{ &page_offset_base, 0 },
>  	{ &vmalloc_base, 0 },
> -	{ &vmemmap_base, 1 },
> +	{ &vmemmap_base, 0 },
>  };
>  
>  /* Get size in bytes used by the memory region */
> @@ -78,6 +78,7 @@ void __init kernel_randomize_memory(void)
>  	unsigned long rand, memory_tb;
>  	struct rnd_state rand_state;
>  	unsigned long remain_entropy;
> +	unsigned long vmemmap_size;
>  
>  	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
>  	vaddr = vaddr_start;
> @@ -109,6 +110,14 @@ void __init kernel_randomize_memory(void)
>  	if (memory_tb < kaslr_regions[0].size_tb)
>  		kaslr_regions[0].size_tb = memory_tb;
>  
> +	/*
> +	 * Calculate how many TB vmemmap region needs, and aligned to
> +	 * 1TB boundary.
> +	 */
> +	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
> +		sizeof(struct page);
> +	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
> +
>  	/* Calculate entropy available between regions */
>  	remain_entropy = vaddr_end - vaddr_start;
>  	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
> -- 
> 2.17.2
> 

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section
  2019-05-08  8:24 ` Baoquan He
@ 2019-05-08  9:04   ` Borislav Petkov
  2019-05-08  9:35     ` Baoquan He
  0 siblings, 1 reply; 6+ messages in thread
From: Borislav Petkov @ 2019-05-08  9:04 UTC (permalink / raw)
  To: Baoquan He
  Cc: linux-kernel, stable, x86, tglx, mingo, hpa, kirill.shutemov, keescook

On Wed, May 08, 2019 at 04:24:18PM +0800, Baoquan He wrote:
> I think this's worth noticing stable tree:
> 
> Cc: stable@vger.kernel.org

Fixes: ?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section
  2019-05-08  9:04   ` Borislav Petkov
@ 2019-05-08  9:35     ` Baoquan He
  2019-05-08 14:47       ` Kirill A. Shutemov
  0 siblings, 1 reply; 6+ messages in thread
From: Baoquan He @ 2019-05-08  9:35 UTC (permalink / raw)
  To: Borislav Petkov
  Cc: linux-kernel, stable, x86, tglx, mingo, hpa, kirill.shutemov, keescook

On 05/08/19 at 11:04am, Borislav Petkov wrote:
> On Wed, May 08, 2019 at 04:24:18PM +0800, Baoquan He wrote:
> > I think this's worth noticing stable tree:
> > 
> > Cc: stable@vger.kernel.org
> 
> Fixes: ?

Not sure which commit validated 5-level.

Hi Kirill,

Is this commit OK?

Fiexes: eedb92abb9bb ("x86/mm: Make virtual memory layout dynamic for CONFIG_X86_5LEVEL=y")

Thanks
Baoquan

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section
  2019-05-08  9:35     ` Baoquan He
@ 2019-05-08 14:47       ` Kirill A. Shutemov
  2019-05-15  1:48         ` Baoquan He
  0 siblings, 1 reply; 6+ messages in thread
From: Kirill A. Shutemov @ 2019-05-08 14:47 UTC (permalink / raw)
  To: Baoquan He
  Cc: Borislav Petkov, linux-kernel, stable, x86, tglx, mingo, hpa,
	kirill.shutemov, keescook

On Wed, May 08, 2019 at 05:35:20PM +0800, Baoquan He wrote:
> On 05/08/19 at 11:04am, Borislav Petkov wrote:
> > On Wed, May 08, 2019 at 04:24:18PM +0800, Baoquan He wrote:
> > > I think this's worth noticing stable tree:
> > > 
> > > Cc: stable@vger.kernel.org
> > 
> > Fixes: ?
> 
> Not sure which commit validated 5-level.
> 
> Hi Kirill,
> 
> Is this commit OK?
> 
> Fiexes: eedb92abb9bb ("x86/mm: Make virtual memory layout dynamic for CONFIG_X86_5LEVEL=y")

Yep.

-- 
 Kirill A. Shutemov

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section
  2019-05-08 14:47       ` Kirill A. Shutemov
@ 2019-05-15  1:48         ` Baoquan He
  0 siblings, 0 replies; 6+ messages in thread
From: Baoquan He @ 2019-05-15  1:48 UTC (permalink / raw)
  To: Kirill A. Shutemov
  Cc: Borislav Petkov, linux-kernel, stable, x86, tglx, mingo, hpa,
	kirill.shutemov, keescook

On 05/08/19 at 05:47pm, Kirill A. Shutemov wrote:
> On Wed, May 08, 2019 at 05:35:20PM +0800, Baoquan He wrote:
> > On 05/08/19 at 11:04am, Borislav Petkov wrote:
> > > On Wed, May 08, 2019 at 04:24:18PM +0800, Baoquan He wrote:
> > > > I think this's worth noticing stable tree:
> > > > 
> > > > Cc: stable@vger.kernel.org
> > > 
> > > Fixes: ?
> > 
> > Not sure which commit validated 5-level.
> > 
> > Hi Kirill,
> > 
> > Is this commit OK?
> > 
> > Fiexes: eedb92abb9bb ("x86/mm: Make virtual memory layout dynamic for CONFIG_X86_5LEVEL=y")
> 
> Yep.

Thanks for confirming, will use it to update patch.

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2019-05-15  1:48 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2019-05-08  8:04 [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section Baoquan He
2019-05-08  8:24 ` Baoquan He
2019-05-08  9:04   ` Borislav Petkov
2019-05-08  9:35     ` Baoquan He
2019-05-08 14:47       ` Kirill A. Shutemov
2019-05-15  1:48         ` Baoquan He

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