[PATCH v3 0/1] correct the inside linear map range during hotplug check

[PATCH v3 0/1] correct the inside linear map range during hotplug check

[Pavel Tatashin]

v3:	- Sync with linux-next where arch_get_mappable_range() was
	  introduced.
v2:	- Added test-by Tyler Hicks
	- Addressed comments from Anshuman Khandual: moved check under
	  IS_ENABLED(CONFIG_RANDOMIZE_BASE), added 
	  WARN_ON(start_linear_pa > end_linear_pa);

Fixes a hotplug error that may occur on systems with CONFIG_RANDOMIZE_BASE
enabled.

Applies against linux-next.

v1:
https://lore.kernel.org/lkml/20210213012316.1525419-1-pasha.tatashin@soleen.com
v2:
https://lore.kernel.org/lkml/20210215192237.362706-1-pasha.tatashin@soleen.com

Pavel Tatashin (1):
  arm64: mm: correct the inside linear map range during hotplug check

 arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

-- 
2.25.1

[PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Pavel Tatashin]

Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
linear map range is not checked correctly.

The start physical address that linear map covers can be actually at the
end of the range because of randomization. Check that and if so reduce it
to 0.

This can be verified on QEMU with setting kaslr-seed to ~0ul:

memstart_offset_seed = 0xffff
START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
END:   __pa(PAGE_END - 1) =  1000bfffffff

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
Tested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
---
 arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index ef7698c4e2f0..0d9c115e427f 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1447,6 +1447,22 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
 struct range arch_get_mappable_range(void)
 {
 	struct range mhp_range;
+	u64 start_linear_pa = __pa(_PAGE_OFFSET(vabits_actual));
+	u64 end_linear_pa = __pa(PAGE_END - 1);
+
+	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+		/*
+		 * Check for a wrap, it is possible because of randomized linear
+		 * mapping the start physical address is actually bigger than
+		 * the end physical address. In this case set start to zero
+		 * because [0, end_linear_pa] range must still be able to cover
+		 * all addressable physical addresses.
+		 */
+		if (start_linear_pa > end_linear_pa)
+			start_linear_pa = 0;
+	}
+
+	WARN_ON(start_linear_pa > end_linear_pa);
 
 	/*
 	 * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
@@ -1454,8 +1470,9 @@ struct range arch_get_mappable_range(void)
 	 * range which can be mapped inside this linear mapping range, must
 	 * also be derived from its end points.
 	 */
-	mhp_range.start = __pa(_PAGE_OFFSET(vabits_actual));
-	mhp_range.end =  __pa(PAGE_END - 1);
+	mhp_range.start = start_linear_pa;
+	mhp_range.end =  end_linear_pa;
+
 	return mhp_range;
 }
 
-- 
2.25.1

Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Will Deacon]

On Tue, Feb 16, 2021 at 10:03:51AM -0500, Pavel Tatashin wrote:
> Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
> linear map range is not checked correctly.
> 
> The start physical address that linear map covers can be actually at the
> end of the range because of randomization. Check that and if so reduce it
> to 0.
> 
> This can be verified on QEMU with setting kaslr-seed to ~0ul:
> 
> memstart_offset_seed = 0xffff
> START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
> END:   __pa(PAGE_END - 1) =  1000bfffffff
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
> Tested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> ---
>  arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)

I tried to queue this as a fix, but unfortunately it doesn't apply.
Please can you send a v4 based on the arm64 for-next/fixes branch?

Thanks,

Will

Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Pavel Tatashin]

On Fri, Feb 19, 2021 at 2:18 PM Will Deacon <will@kernel.org> wrote:
>
> On Tue, Feb 16, 2021 at 10:03:51AM -0500, Pavel Tatashin wrote:
> > Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
> > linear map range is not checked correctly.
> >
> > The start physical address that linear map covers can be actually at the
> > end of the range because of randomization. Check that and if so reduce it
> > to 0.
> >
> > This can be verified on QEMU with setting kaslr-seed to ~0ul:
> >
> > memstart_offset_seed = 0xffff
> > START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
> > END:   __pa(PAGE_END - 1) =  1000bfffffff
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> > Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
> > Tested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> > ---
> >  arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
> >  1 file changed, 19 insertions(+), 2 deletions(-)
>
> I tried to queue this as a fix, but unfortunately it doesn't apply.
> Please can you send a v4 based on the arm64 for-next/fixes branch?

Hi Will,

The previous version, that is not built against linux-next would still
applies against current mainlein/for-next/fixes

https://lore.kernel.org/lkml/20210215192237.362706-2-pasha.tatashin@soleen.com/

I just tried it. I think it would make sense to take v2 fix, so it
could also be backported to stables.

Thank you,
Pasha

Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Will Deacon]

On Fri, Feb 19, 2021 at 02:44:49PM -0500, Pavel Tatashin wrote:
> On Fri, Feb 19, 2021 at 2:18 PM Will Deacon <will@kernel.org> wrote:
> >
> > On Tue, Feb 16, 2021 at 10:03:51AM -0500, Pavel Tatashin wrote:
> > > Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
> > > linear map range is not checked correctly.
> > >
> > > The start physical address that linear map covers can be actually at the
> > > end of the range because of randomization. Check that and if so reduce it
> > > to 0.
> > >
> > > This can be verified on QEMU with setting kaslr-seed to ~0ul:
> > >
> > > memstart_offset_seed = 0xffff
> > > START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
> > > END:   __pa(PAGE_END - 1) =  1000bfffffff
> > >
> > > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> > > Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
> > > Tested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> > > ---
> > >  arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
> > >  1 file changed, 19 insertions(+), 2 deletions(-)
> >
> > I tried to queue this as a fix, but unfortunately it doesn't apply.
> > Please can you send a v4 based on the arm64 for-next/fixes branch?
> 
> The previous version, that is not built against linux-next would still
> applies against current mainlein/for-next/fixes
> 
> https://lore.kernel.org/lkml/20210215192237.362706-2-pasha.tatashin@soleen.com/
> 
> I just tried it. I think it would make sense to take v2 fix, so it
> could also be backported to stables.

Taking that won't help either though, because it will just explode when
it meets 'mm' in Linus's tree.

So here's what I think we need to do:

  - I'll apply your v3 at -rc1
  - You can send backports based on your -v2 for stable once the v3 has
    been merged upstream.

Sound good?

Will

Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Pavel Tatashin]

> Taking that won't help either though, because it will just explode when
> it meets 'mm' in Linus's tree.
>
> So here's what I think we need to do:
>
>   - I'll apply your v3 at -rc1
>   - You can send backports based on your -v2 for stable once the v3 has
>     been merged upstream.
>
> Sound good?

Sounds good, I will send backport once v3 lands in Linus's tree.

Thanks,
Pasha

>
> Will

Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Anshuman Khandual]

On 2/16/21 8:33 PM, Pavel Tatashin wrote:
> Memory hotplug may fail on systems with CONFIG_RANDOMIZE_BASE because the
> linear map range is not checked correctly.
> 
> The start physical address that linear map covers can be actually at the
> end of the range because of randomization. Check that and if so reduce it
> to 0.
> 
> This can be verified on QEMU with setting kaslr-seed to ~0ul:
> 
> memstart_offset_seed = 0xffff
> START: __pa(_PAGE_OFFSET(vabits_actual)) = ffff9000c0000000
> END:   __pa(PAGE_END - 1) =  1000bfffffff

This would have tripped the check in mhp_get_pluggable_range()
with errors something like here, which is expected.

Hotplug memory [0x680000000-0x688000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x6c0000000-0x6c8000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x700000000-0x708000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x780000000-0x788000000] exceeds maximum addressable range [0x0-0x0]
Hotplug memory [0x7c0000000-0x7c8000000] exceeds maximum addressable range [0x0-0x0]

> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> Fixes: 58284a901b42 ("arm64/mm: Validate hotplug range before creating linear mapping")
> Tested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> ---
>  arch/arm64/mm/mmu.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ef7698c4e2f0..0d9c115e427f 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1447,6 +1447,22 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
>  struct range arch_get_mappable_range(void)
>  {
>  	struct range mhp_range;
> +	u64 start_linear_pa = __pa(_PAGE_OFFSET(vabits_actual));
> +	u64 end_linear_pa = __pa(PAGE_END - 1);
> +
> +	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> +		/*
> +		 * Check for a wrap, it is possible because of randomized linear
> +		 * mapping the start physical address is actually bigger than
> +		 * the end physical address. In this case set start to zero
> +		 * because [0, end_linear_pa] range must still be able to cover
> +		 * all addressable physical addresses.
> +		 */
> +		if (start_linear_pa > end_linear_pa)
> +			start_linear_pa = 0;
> +	}
> +
> +	WARN_ON(start_linear_pa > end_linear_pa);
>  
>  	/*
>  	 * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
> @@ -1454,8 +1470,9 @@ struct range arch_get_mappable_range(void)
>  	 * range which can be mapped inside this linear mapping range, must
>  	 * also be derived from its end points.
>  	 */
> -	mhp_range.start = __pa(_PAGE_OFFSET(vabits_actual));
> -	mhp_range.end =  __pa(PAGE_END - 1);
> +	mhp_range.start = start_linear_pa;
> +	mhp_range.end =  end_linear_pa;
> +
>  	return mhp_range;
>  }

LGTM.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

Re: [PATCH v3 1/1] arm64: mm: correct the inside linear map range during hotplug check

[Pavel Tatashin]

Hi Will,

Could you please take this patch now that the dependencies landed in
the mainline?

Thank you,
Pasha

On Mon, Feb 22, 2021 at 9:17 AM Pavel Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> > Taking that won't help either though, because it will just explode when
> > it meets 'mm' in Linus's tree.
> >
> > So here's what I think we need to do:
> >
> >   - I'll apply your v3 at -rc1
> >   - You can send backports based on your -v2 for stable once the v3 has
> >     been merged upstream.
> >
> > Sound good?
>
> Sounds good, I will send backport once v3 lands in Linus's tree.
>
> Thanks,
> Pasha
>
> >
> > Will

Re: [PATCH v3 0/1] correct the inside linear map range during hotplug check

[Will Deacon]

On Tue, 16 Feb 2021 10:03:50 -0500, Pavel Tatashin wrote:
> v3:	- Sync with linux-next where arch_get_mappable_range() was
> 	  introduced.
> v2:	- Added test-by Tyler Hicks
> 	- Addressed comments from Anshuman Khandual: moved check under
> 	  IS_ENABLED(CONFIG_RANDOMIZE_BASE), added
> 	  WARN_ON(start_linear_pa > end_linear_pa);
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: mm: correct the inside linear map range during hotplug check
      https://git.kernel.org/arm64/c/ee7febce0519

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev