[PATCH stable 5.4] arm64: mm: account for hotplug memory when randomizing the linear region

[PATCH stable 5.4] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

From: Ard Biesheuvel <ardb@kernel.org>

commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream

As a hardening measure, we currently randomize the placement of
physical memory inside the linear region when KASLR is in effect.
Since the random offset at which to place the available physical
memory inside the linear region is chosen early at boot, it is
based on the memblock description of memory, which does not cover
hotplug memory. The consequence of this is that the randomization
offset may be chosen such that any hotplugged memory located above
memblock_end_of_DRAM() that appears later is pushed off the end of
the linear region, where it cannot be accessed.

So let's limit this randomization of the linear region to ensure
that this can no longer happen, by using the CPU's addressable PA
range instead. As it is guaranteed that no hotpluggable memory will
appear that falls outside of that range, we can safely put this PA
range sized window anywhere in the linear region.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 arch/arm64/mm/init.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index cbcac03c0e0d..a6034645d6f7 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -392,15 +392,18 @@ void __init arm64_memblock_init(void)
 
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
 		extern u16 memstart_offset_seed;
-		u64 range = linear_region_size -
-			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
+		u64 mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
+		int parange = cpuid_feature_extract_unsigned_field(
+					mmfr0, ID_AA64MMFR0_PARANGE_SHIFT);
+		s64 range = linear_region_size -
+			    BIT(id_aa64mmfr0_parange_to_phys_shift(parange));
 
 		/*
 		 * If the size of the linear region exceeds, by a sufficient
-		 * margin, the size of the region that the available physical
-		 * memory spans, randomize the linear region as well.
+		 * margin, the size of the region that the physical memory can
+		 * span, randomize the linear region as well.
 		 */
-		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
+		if (memstart_offset_seed > 0 && range >= (s64)ARM64_MEMSTART_ALIGN) {
 			range /= ARM64_MEMSTART_ALIGN;
 			memstart_addr -= ARM64_MEMSTART_ALIGN *
 					 ((range * memstart_offset_seed) >> 16);
-- 
2.43.0

[PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

From: Ard Biesheuvel <ardb@kernel.org>

commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream

As a hardening measure, we currently randomize the placement of
physical memory inside the linear region when KASLR is in effect.
Since the random offset at which to place the available physical
memory inside the linear region is chosen early at boot, it is
based on the memblock description of memory, which does not cover
hotplug memory. The consequence of this is that the randomization
offset may be chosen such that any hotplugged memory located above
memblock_end_of_DRAM() that appears later is pushed off the end of
the linear region, where it cannot be accessed.

So let's limit this randomization of the linear region to ensure
that this can no longer happen, by using the CPU's addressable PA
range instead. As it is guaranteed that no hotpluggable memory will
appear that falls outside of that range, we can safely put this PA
range sized window anywhere in the linear region.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 arch/arm64/mm/init.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 80cc79760e8e..09c219aa9d78 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -401,15 +401,18 @@ void __init arm64_memblock_init(void)
 
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
 		extern u16 memstart_offset_seed;
-		u64 range = linear_region_size -
-			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
+		u64 mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
+		int parange = cpuid_feature_extract_unsigned_field(
+					mmfr0, ID_AA64MMFR0_PARANGE_SHIFT);
+		s64 range = linear_region_size -
+			    BIT(id_aa64mmfr0_parange_to_phys_shift(parange));
 
 		/*
 		 * If the size of the linear region exceeds, by a sufficient
-		 * margin, the size of the region that the available physical
-		 * memory spans, randomize the linear region as well.
+		 * margin, the size of the region that the physical memory can
+		 * span, randomize the linear region as well.
 		 */
-		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
+		if (memstart_offset_seed > 0 && range >= (s64)ARM64_MEMSTART_ALIGN) {
 			range /= ARM64_MEMSTART_ALIGN;
 			memstart_addr -= ARM64_MEMSTART_ALIGN *
 					 ((range * memstart_offset_seed) >> 16);
-- 
2.43.0

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/9/25 08:54, Florian Fainelli wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> 
> As a hardening measure, we currently randomize the placement of
> physical memory inside the linear region when KASLR is in effect.
> Since the random offset at which to place the available physical
> memory inside the linear region is chosen early at boot, it is
> based on the memblock description of memory, which does not cover
> hotplug memory. The consequence of this is that the randomization
> offset may be chosen such that any hotplugged memory located above
> memblock_end_of_DRAM() that appears later is pushed off the end of
> the linear region, where it cannot be accessed.
> 
> So let's limit this randomization of the linear region to ensure
> that this can no longer happen, by using the CPU's addressable PA
> range instead. As it is guaranteed that no hotpluggable memory will
> appear that falls outside of that range, we can safely put this PA
> range sized window anywhere in the linear region.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>

Forgot to update the patch subject, but this one is for 5.10.
-- 
Florian

Re: [PATCH stable 5.4] arm64: mm: account for hotplug memory when randomizing the linear region

[Greg KH]

On Thu, Jan 09, 2025 at 08:54:16AM -0800, Florian Fainelli wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> 
> As a hardening measure, we currently randomize the placement of
> physical memory inside the linear region when KASLR is in effect.
> Since the random offset at which to place the available physical
> memory inside the linear region is chosen early at boot, it is
> based on the memblock description of memory, which does not cover
> hotplug memory. The consequence of this is that the randomization
> offset may be chosen such that any hotplugged memory located above
> memblock_end_of_DRAM() that appears later is pushed off the end of
> the linear region, where it cannot be accessed.
> 
> So let's limit this randomization of the linear region to ensure
> that this can no longer happen, by using the CPU's addressable PA
> range instead. As it is guaranteed that no hotpluggable memory will
> appear that falls outside of that range, we can safely put this PA
> range sized window anywhere in the linear region.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> ---
>  arch/arm64/mm/init.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index cbcac03c0e0d..a6034645d6f7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -392,15 +392,18 @@ void __init arm64_memblock_init(void)
>  
>  	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
>  		extern u16 memstart_offset_seed;
> -		u64 range = linear_region_size -
> -			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
> +		u64 mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
> +		int parange = cpuid_feature_extract_unsigned_field(
> +					mmfr0, ID_AA64MMFR0_PARANGE_SHIFT);
> +		s64 range = linear_region_size -
> +			    BIT(id_aa64mmfr0_parange_to_phys_shift(parange));
>  
>  		/*
>  		 * If the size of the linear region exceeds, by a sufficient
> -		 * margin, the size of the region that the available physical
> -		 * memory spans, randomize the linear region as well.
> +		 * margin, the size of the region that the physical memory can
> +		 * span, randomize the linear region as well.
>  		 */
> -		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> +		if (memstart_offset_seed > 0 && range >= (s64)ARM64_MEMSTART_ALIGN) {
>  			range /= ARM64_MEMSTART_ALIGN;
>  			memstart_addr -= ARM64_MEMSTART_ALIGN *
>  					 ((range * memstart_offset_seed) >> 16);
> -- 
> 2.43.0
> 
> 

You are not providing any information as to WHY this is needed in stable
kernels at all.  It just looks like an unsolicted backport with no
changes from upstream, yet no hint as to any bug it fixes.

And you all really have hotpluggable memory on systems that are running
th is old kernel?  Why are they not using newer kernels if they need
this?  Surely lots of other bugs they need are resolved there, right?

thanks,

greg k-h

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Greg KH]

On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
> On 1/9/25 08:54, Florian Fainelli wrote:
> > From: Ard Biesheuvel <ardb@kernel.org>
> > 
> > commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> > 
> > As a hardening measure, we currently randomize the placement of
> > physical memory inside the linear region when KASLR is in effect.
> > Since the random offset at which to place the available physical
> > memory inside the linear region is chosen early at boot, it is
> > based on the memblock description of memory, which does not cover
> > hotplug memory. The consequence of this is that the randomization
> > offset may be chosen such that any hotplugged memory located above
> > memblock_end_of_DRAM() that appears later is pushed off the end of
> > the linear region, where it cannot be accessed.
> > 
> > So let's limit this randomization of the linear region to ensure
> > that this can no longer happen, by using the CPU's addressable PA
> > range instead. As it is guaranteed that no hotpluggable memory will
> > appear that falls outside of that range, we can safely put this PA
> > range sized window anywhere in the linear region.
> > 
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Steven Price <steven.price@arm.com>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> 
> Forgot to update the patch subject, but this one is for 5.10.

You also forgot to tell us _why_ this is needed :(

thanks,

greg k-h

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/12/2025 3:54 AM, Greg KH wrote:
> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
>> On 1/9/25 08:54, Florian Fainelli wrote:
>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>
>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
>>>
>>> As a hardening measure, we currently randomize the placement of
>>> physical memory inside the linear region when KASLR is in effect.
>>> Since the random offset at which to place the available physical
>>> memory inside the linear region is chosen early at boot, it is
>>> based on the memblock description of memory, which does not cover
>>> hotplug memory. The consequence of this is that the randomization
>>> offset may be chosen such that any hotplugged memory located above
>>> memblock_end_of_DRAM() that appears later is pushed off the end of
>>> the linear region, where it cannot be accessed.
>>>
>>> So let's limit this randomization of the linear region to ensure
>>> that this can no longer happen, by using the CPU's addressable PA
>>> range instead. As it is guaranteed that no hotpluggable memory will
>>> appear that falls outside of that range, we can safely put this PA
>>> range sized window anywhere in the linear region.
>>>
>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>>> Cc: Will Deacon <will@kernel.org>
>>> Cc: Steven Price <steven.price@arm.com>
>>> Cc: Robin Murphy <robin.murphy@arm.com>
>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>>
>> Forgot to update the patch subject, but this one is for 5.10.
> 
> You also forgot to tell us _why_ this is needed :(

This is explained in the second part of the first paragraph:

The consequence of this is that the randomization offset may be chosen 
such that any hotplugged memory located above memblock_end_of_DRAM() 
that appears later is pushed off the end of the linear region, where it 
cannot be accessed.

We use both memory hotplug and KASLR on our systems and that's how we 
eventually found out about the bug.
-- 
Florian

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Greg KH]

On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
> 
> 
> On 1/12/2025 3:54 AM, Greg KH wrote:
> > On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
> > > On 1/9/25 08:54, Florian Fainelli wrote:
> > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > > 
> > > > commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> > > > 
> > > > As a hardening measure, we currently randomize the placement of
> > > > physical memory inside the linear region when KASLR is in effect.
> > > > Since the random offset at which to place the available physical
> > > > memory inside the linear region is chosen early at boot, it is
> > > > based on the memblock description of memory, which does not cover
> > > > hotplug memory. The consequence of this is that the randomization
> > > > offset may be chosen such that any hotplugged memory located above
> > > > memblock_end_of_DRAM() that appears later is pushed off the end of
> > > > the linear region, where it cannot be accessed.
> > > > 
> > > > So let's limit this randomization of the linear region to ensure
> > > > that this can no longer happen, by using the CPU's addressable PA
> > > > range instead. As it is guaranteed that no hotpluggable memory will
> > > > appear that falls outside of that range, we can safely put this PA
> > > > range sized window anywhere in the linear region.
> > > > 
> > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> > > > Cc: Will Deacon <will@kernel.org>
> > > > Cc: Steven Price <steven.price@arm.com>
> > > > Cc: Robin Murphy <robin.murphy@arm.com>
> > > > Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> > > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > > > Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> > > 
> > > Forgot to update the patch subject, but this one is for 5.10.
> > 
> > You also forgot to tell us _why_ this is needed :(
> 
> This is explained in the second part of the first paragraph:
> 
> The consequence of this is that the randomization offset may be chosen such
> that any hotplugged memory located above memblock_end_of_DRAM() that appears
> later is pushed off the end of the linear region, where it cannot be
> accessed.
> 
> We use both memory hotplug and KASLR on our systems and that's how we
> eventually found out about the bug.

And you still have 5.10.y ARM64 systems that need this?  Why not move to
a newer kernel version already?

Anyway, I need an ack from the ARM64 maintainers that this is ok to
apply here before I can take it.

thanks,

greg k-h

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/20/2025 5:59 AM, Greg KH wrote:
> On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
>>
>>
>> On 1/12/2025 3:54 AM, Greg KH wrote:
>>> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
>>>> On 1/9/25 08:54, Florian Fainelli wrote:
>>>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>>>
>>>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
>>>>>
>>>>> As a hardening measure, we currently randomize the placement of
>>>>> physical memory inside the linear region when KASLR is in effect.
>>>>> Since the random offset at which to place the available physical
>>>>> memory inside the linear region is chosen early at boot, it is
>>>>> based on the memblock description of memory, which does not cover
>>>>> hotplug memory. The consequence of this is that the randomization
>>>>> offset may be chosen such that any hotplugged memory located above
>>>>> memblock_end_of_DRAM() that appears later is pushed off the end of
>>>>> the linear region, where it cannot be accessed.
>>>>>
>>>>> So let's limit this randomization of the linear region to ensure
>>>>> that this can no longer happen, by using the CPU's addressable PA
>>>>> range instead. As it is guaranteed that no hotpluggable memory will
>>>>> appear that falls outside of that range, we can safely put this PA
>>>>> range sized window anywhere in the linear region.
>>>>>
>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>>>>> Cc: Will Deacon <will@kernel.org>
>>>>> Cc: Steven Price <steven.price@arm.com>
>>>>> Cc: Robin Murphy <robin.murphy@arm.com>
>>>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
>>>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>>>>
>>>> Forgot to update the patch subject, but this one is for 5.10.
>>>
>>> You also forgot to tell us _why_ this is needed :(
>>
>> This is explained in the second part of the first paragraph:
>>
>> The consequence of this is that the randomization offset may be chosen such
>> that any hotplugged memory located above memblock_end_of_DRAM() that appears
>> later is pushed off the end of the linear region, where it cannot be
>> accessed.
>>
>> We use both memory hotplug and KASLR on our systems and that's how we
>> eventually found out about the bug.
> 
> And you still have 5.10.y ARM64 systems that need this?  Why not move to
> a newer kernel version already?

We still have ARM64 systems running 5.4 that need this, and the same bug 
applies to 5.10 that we used to support but dropped in favor of 
5.15/6.1. Those are the kernel versions used by Android, and Android TV 
in particular, so it's kind of the way it goes for us.

> 
> Anyway, I need an ack from the ARM64 maintainers that this is ok to
> apply here before I can take it.

Just out of curiosity, the change is pretty innocuous and simple to 
review, why the extra scrutiny needed here?
-- 
Florian

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Greg KH]

On Mon, Jan 20, 2025 at 08:33:12AM -0800, Florian Fainelli wrote:
> 
> 
> On 1/20/2025 5:59 AM, Greg KH wrote:
> > On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
> > > 
> > > 
> > > On 1/12/2025 3:54 AM, Greg KH wrote:
> > > > On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
> > > > > On 1/9/25 08:54, Florian Fainelli wrote:
> > > > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > > > > 
> > > > > > commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> > > > > > 
> > > > > > As a hardening measure, we currently randomize the placement of
> > > > > > physical memory inside the linear region when KASLR is in effect.
> > > > > > Since the random offset at which to place the available physical
> > > > > > memory inside the linear region is chosen early at boot, it is
> > > > > > based on the memblock description of memory, which does not cover
> > > > > > hotplug memory. The consequence of this is that the randomization
> > > > > > offset may be chosen such that any hotplugged memory located above
> > > > > > memblock_end_of_DRAM() that appears later is pushed off the end of
> > > > > > the linear region, where it cannot be accessed.
> > > > > > 
> > > > > > So let's limit this randomization of the linear region to ensure
> > > > > > that this can no longer happen, by using the CPU's addressable PA
> > > > > > range instead. As it is guaranteed that no hotpluggable memory will
> > > > > > appear that falls outside of that range, we can safely put this PA
> > > > > > range sized window anywhere in the linear region.
> > > > > > 
> > > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > > > Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> > > > > > Cc: Will Deacon <will@kernel.org>
> > > > > > Cc: Steven Price <steven.price@arm.com>
> > > > > > Cc: Robin Murphy <robin.murphy@arm.com>
> > > > > > Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> > > > > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > > > > > Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> > > > > 
> > > > > Forgot to update the patch subject, but this one is for 5.10.
> > > > 
> > > > You also forgot to tell us _why_ this is needed :(
> > > 
> > > This is explained in the second part of the first paragraph:
> > > 
> > > The consequence of this is that the randomization offset may be chosen such
> > > that any hotplugged memory located above memblock_end_of_DRAM() that appears
> > > later is pushed off the end of the linear region, where it cannot be
> > > accessed.
> > > 
> > > We use both memory hotplug and KASLR on our systems and that's how we
> > > eventually found out about the bug.
> > 
> > And you still have 5.10.y ARM64 systems that need this?  Why not move to
> > a newer kernel version already?
> 
> We still have ARM64 systems running 5.4 that need this, and the same bug
> applies to 5.10 that we used to support but dropped in favor of 5.15/6.1.
> Those are the kernel versions used by Android, and Android TV in particular,
> so it's kind of the way it goes for us.
> 
> > 
> > Anyway, I need an ack from the ARM64 maintainers that this is ok to
> > apply here before I can take it.
> 
> Just out of curiosity, the change is pretty innocuous and simple to review,
> why the extra scrutiny needed here?

Why shouldn't the maintainers review a proposed backport patch for core
kernel code that affects everyone who uses that arch?

thanks,

greg k-h

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/29/25 01:17, Greg KH wrote:
> On Mon, Jan 20, 2025 at 08:33:12AM -0800, Florian Fainelli wrote:
>>
>>
>> On 1/20/2025 5:59 AM, Greg KH wrote:
>>> On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
>>>>
>>>>
>>>> On 1/12/2025 3:54 AM, Greg KH wrote:
>>>>> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
>>>>>> On 1/9/25 08:54, Florian Fainelli wrote:
>>>>>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>>>>>
>>>>>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
>>>>>>>
>>>>>>> As a hardening measure, we currently randomize the placement of
>>>>>>> physical memory inside the linear region when KASLR is in effect.
>>>>>>> Since the random offset at which to place the available physical
>>>>>>> memory inside the linear region is chosen early at boot, it is
>>>>>>> based on the memblock description of memory, which does not cover
>>>>>>> hotplug memory. The consequence of this is that the randomization
>>>>>>> offset may be chosen such that any hotplugged memory located above
>>>>>>> memblock_end_of_DRAM() that appears later is pushed off the end of
>>>>>>> the linear region, where it cannot be accessed.
>>>>>>>
>>>>>>> So let's limit this randomization of the linear region to ensure
>>>>>>> that this can no longer happen, by using the CPU's addressable PA
>>>>>>> range instead. As it is guaranteed that no hotpluggable memory will
>>>>>>> appear that falls outside of that range, we can safely put this PA
>>>>>>> range sized window anywhere in the linear region.
>>>>>>>
>>>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>>>>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>>>>>>> Cc: Will Deacon <will@kernel.org>
>>>>>>> Cc: Steven Price <steven.price@arm.com>
>>>>>>> Cc: Robin Murphy <robin.murphy@arm.com>
>>>>>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
>>>>>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>>>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>>>>>>
>>>>>> Forgot to update the patch subject, but this one is for 5.10.
>>>>>
>>>>> You also forgot to tell us _why_ this is needed :(
>>>>
>>>> This is explained in the second part of the first paragraph:
>>>>
>>>> The consequence of this is that the randomization offset may be chosen such
>>>> that any hotplugged memory located above memblock_end_of_DRAM() that appears
>>>> later is pushed off the end of the linear region, where it cannot be
>>>> accessed.
>>>>
>>>> We use both memory hotplug and KASLR on our systems and that's how we
>>>> eventually found out about the bug.
>>>
>>> And you still have 5.10.y ARM64 systems that need this?  Why not move to
>>> a newer kernel version already?
>>
>> We still have ARM64 systems running 5.4 that need this, and the same bug
>> applies to 5.10 that we used to support but dropped in favor of 5.15/6.1.
>> Those are the kernel versions used by Android, and Android TV in particular,
>> so it's kind of the way it goes for us.
>>
>>>
>>> Anyway, I need an ack from the ARM64 maintainers that this is ok to
>>> apply here before I can take it.
>>
>> Just out of curiosity, the change is pretty innocuous and simple to review,
>> why the extra scrutiny needed here?
> 
> Why shouldn't the maintainers review a proposed backport patch for core
> kernel code that affects everyone who uses that arch?

They should, but they are not, we can keep sending messages like those 
in the hope that someone does, but clearly that is not working at the 
moment.

This patch cherry picked cleanly into 5.4 and 5.10 maybe they just trust 
whoever submit stable bugfixes to have done their due diligence, too, I 
don't know how to get that moving now but it fixes a real problem we 
observed.

-- 
Florian

Re: [PATCH stable 5.4] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/12/25 03:53, Greg KH wrote:
> On Thu, Jan 09, 2025 at 08:54:16AM -0800, Florian Fainelli wrote:
>> From: Ard Biesheuvel <ardb@kernel.org>
>>
>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
>>
>> As a hardening measure, we currently randomize the placement of
>> physical memory inside the linear region when KASLR is in effect.
>> Since the random offset at which to place the available physical
>> memory inside the linear region is chosen early at boot, it is
>> based on the memblock description of memory, which does not cover
>> hotplug memory. The consequence of this is that the randomization
>> offset may be chosen such that any hotplugged memory located above
>> memblock_end_of_DRAM() that appears later is pushed off the end of
>> the linear region, where it cannot be accessed.
>>
>> So let's limit this randomization of the linear region to ensure
>> that this can no longer happen, by using the CPU's addressable PA
>> range instead. As it is guaranteed that no hotpluggable memory will
>> appear that falls outside of that range, we can safely put this PA
>> range sized window anywhere in the linear region.
>>
>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Steven Price <steven.price@arm.com>
>> Cc: Robin Murphy <robin.murphy@arm.com>
>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>> ---
>>   arch/arm64/mm/init.c | 13 ++++++++-----
>>   1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index cbcac03c0e0d..a6034645d6f7 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -392,15 +392,18 @@ void __init arm64_memblock_init(void)
>>   
>>   	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
>>   		extern u16 memstart_offset_seed;
>> -		u64 range = linear_region_size -
>> -			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
>> +		u64 mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
>> +		int parange = cpuid_feature_extract_unsigned_field(
>> +					mmfr0, ID_AA64MMFR0_PARANGE_SHIFT);
>> +		s64 range = linear_region_size -
>> +			    BIT(id_aa64mmfr0_parange_to_phys_shift(parange));
>>   
>>   		/*
>>   		 * If the size of the linear region exceeds, by a sufficient
>> -		 * margin, the size of the region that the available physical
>> -		 * memory spans, randomize the linear region as well.
>> +		 * margin, the size of the region that the physical memory can
>> +		 * span, randomize the linear region as well.
>>   		 */
>> -		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
>> +		if (memstart_offset_seed > 0 && range >= (s64)ARM64_MEMSTART_ALIGN) {
>>   			range /= ARM64_MEMSTART_ALIGN;
>>   			memstart_addr -= ARM64_MEMSTART_ALIGN *
>>   					 ((range * memstart_offset_seed) >> 16);
>> -- 
>> 2.43.0
>>
>>
> 
> You are not providing any information as to WHY this is needed in stable
> kernels at all.  It just looks like an unsolicted backport with no
> changes from upstream, yet no hint as to any bug it fixes.

See the response in the other thread.

> 
> And you all really have hotpluggable memory on systems that are running
> th is old kernel?  Why are they not using newer kernels if they need
> this?  Surely lots of other bugs they need are resolved there, right?

Believe it or not, but memory hotplug works really well for us, in a 
somewhat limited configuration on the 5.4 kernel whereby we simply plug 
memory, and never unplug it thereafter, but still, we have not had to 
carry hotplug related patches other than this one.

Trying to be a good citizen here: one of my colleague has identified an 
upstream fix that works, that we got tested, cherry picked cleanly into 
both 5.4 and 5.10, so it's not even like there was any fuzz.

I was sort of hoping that giving my history of regularly testing stable 
kernels for the past years, as well as submitting a fair amount of 
targeted bug fixes to the stable branches that there would be some level 
of trust here.

Thanks
-- 
Florian

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Ard Biesheuvel]

On Wed, 29 Jan 2025 at 18:45, Florian Fainelli
<florian.fainelli@broadcom.com> wrote:
>
> On 1/29/25 01:17, Greg KH wrote:
> > On Mon, Jan 20, 2025 at 08:33:12AM -0800, Florian Fainelli wrote:
> >>
> >>
> >> On 1/20/2025 5:59 AM, Greg KH wrote:
> >>> On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
> >>>>
> >>>>
> >>>> On 1/12/2025 3:54 AM, Greg KH wrote:
> >>>>> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
> >>>>>> On 1/9/25 08:54, Florian Fainelli wrote:
> >>>>>>> From: Ard Biesheuvel <ardb@kernel.org>
> >>>>>>>
> >>>>>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> >>>>>>>
> >>>>>>> As a hardening measure, we currently randomize the placement of
> >>>>>>> physical memory inside the linear region when KASLR is in effect.
> >>>>>>> Since the random offset at which to place the available physical
> >>>>>>> memory inside the linear region is chosen early at boot, it is
> >>>>>>> based on the memblock description of memory, which does not cover
> >>>>>>> hotplug memory. The consequence of this is that the randomization
> >>>>>>> offset may be chosen such that any hotplugged memory located above
> >>>>>>> memblock_end_of_DRAM() that appears later is pushed off the end of
> >>>>>>> the linear region, where it cannot be accessed.
> >>>>>>>
> >>>>>>> So let's limit this randomization of the linear region to ensure
> >>>>>>> that this can no longer happen, by using the CPU's addressable PA
> >>>>>>> range instead. As it is guaranteed that no hotpluggable memory will
> >>>>>>> appear that falls outside of that range, we can safely put this PA
> >>>>>>> range sized window anywhere in the linear region.
> >>>>>>>
> >>>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >>>>>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> >>>>>>> Cc: Will Deacon <will@kernel.org>
> >>>>>>> Cc: Steven Price <steven.price@arm.com>
> >>>>>>> Cc: Robin Murphy <robin.murphy@arm.com>
> >>>>>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> >>>>>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> >>>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> >>>>>>
> >>>>>> Forgot to update the patch subject, but this one is for 5.10.
> >>>>>
> >>>>> You also forgot to tell us _why_ this is needed :(
> >>>>
> >>>> This is explained in the second part of the first paragraph:
> >>>>
> >>>> The consequence of this is that the randomization offset may be chosen such
> >>>> that any hotplugged memory located above memblock_end_of_DRAM() that appears
> >>>> later is pushed off the end of the linear region, where it cannot be
> >>>> accessed.
> >>>>
> >>>> We use both memory hotplug and KASLR on our systems and that's how we
> >>>> eventually found out about the bug.
> >>>
> >>> And you still have 5.10.y ARM64 systems that need this?  Why not move to
> >>> a newer kernel version already?
> >>
> >> We still have ARM64 systems running 5.4 that need this, and the same bug
> >> applies to 5.10 that we used to support but dropped in favor of 5.15/6.1.
> >> Those are the kernel versions used by Android, and Android TV in particular,
> >> so it's kind of the way it goes for us.
> >>
> >>>
> >>> Anyway, I need an ack from the ARM64 maintainers that this is ok to
> >>> apply here before I can take it.
> >>
> >> Just out of curiosity, the change is pretty innocuous and simple to review,
> >> why the extra scrutiny needed here?
> >
> > Why shouldn't the maintainers review a proposed backport patch for core
> > kernel code that affects everyone who uses that arch?
>
> They should, but they are not, we can keep sending messages like those
> in the hope that someone does, but clearly that is not working at the
> moment.
>
> This patch cherry picked cleanly into 5.4 and 5.10 maybe they just trust
> whoever submit stable bugfixes to have done their due diligence, too, I
> don't know how to get that moving now but it fixes a real problem we
> observed.
>

FWIW, I understand why this might be useful when running under a
non-KVM hypervisor that relies on memory hotplug to perform resource
balancing between VMs. But the upshot of this change is that existing
systems that do not rely on memory hotplug at all will suddenly lose
any randomization of the linear map if its CPU happens to be able to
address more than ~40 bits of physical memory. So I'm not convinced
this is a change we should make for these older kernels.

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/29/25 14:15, Ard Biesheuvel wrote:
> On Wed, 29 Jan 2025 at 18:45, Florian Fainelli
> <florian.fainelli@broadcom.com> wrote:
>>
>> On 1/29/25 01:17, Greg KH wrote:
>>> On Mon, Jan 20, 2025 at 08:33:12AM -0800, Florian Fainelli wrote:
>>>>
>>>>
>>>> On 1/20/2025 5:59 AM, Greg KH wrote:
>>>>> On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
>>>>>>
>>>>>>
>>>>>> On 1/12/2025 3:54 AM, Greg KH wrote:
>>>>>>> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
>>>>>>>> On 1/9/25 08:54, Florian Fainelli wrote:
>>>>>>>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>>>>>>>
>>>>>>>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
>>>>>>>>>
>>>>>>>>> As a hardening measure, we currently randomize the placement of
>>>>>>>>> physical memory inside the linear region when KASLR is in effect.
>>>>>>>>> Since the random offset at which to place the available physical
>>>>>>>>> memory inside the linear region is chosen early at boot, it is
>>>>>>>>> based on the memblock description of memory, which does not cover
>>>>>>>>> hotplug memory. The consequence of this is that the randomization
>>>>>>>>> offset may be chosen such that any hotplugged memory located above
>>>>>>>>> memblock_end_of_DRAM() that appears later is pushed off the end of
>>>>>>>>> the linear region, where it cannot be accessed.
>>>>>>>>>
>>>>>>>>> So let's limit this randomization of the linear region to ensure
>>>>>>>>> that this can no longer happen, by using the CPU's addressable PA
>>>>>>>>> range instead. As it is guaranteed that no hotpluggable memory will
>>>>>>>>> appear that falls outside of that range, we can safely put this PA
>>>>>>>>> range sized window anywhere in the linear region.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>>>>>>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>>>>>>>>> Cc: Will Deacon <will@kernel.org>
>>>>>>>>> Cc: Steven Price <steven.price@arm.com>
>>>>>>>>> Cc: Robin Murphy <robin.murphy@arm.com>
>>>>>>>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
>>>>>>>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>>>>>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>>>>>>>>
>>>>>>>> Forgot to update the patch subject, but this one is for 5.10.
>>>>>>>
>>>>>>> You also forgot to tell us _why_ this is needed :(
>>>>>>
>>>>>> This is explained in the second part of the first paragraph:
>>>>>>
>>>>>> The consequence of this is that the randomization offset may be chosen such
>>>>>> that any hotplugged memory located above memblock_end_of_DRAM() that appears
>>>>>> later is pushed off the end of the linear region, where it cannot be
>>>>>> accessed.
>>>>>>
>>>>>> We use both memory hotplug and KASLR on our systems and that's how we
>>>>>> eventually found out about the bug.
>>>>>
>>>>> And you still have 5.10.y ARM64 systems that need this?  Why not move to
>>>>> a newer kernel version already?
>>>>
>>>> We still have ARM64 systems running 5.4 that need this, and the same bug
>>>> applies to 5.10 that we used to support but dropped in favor of 5.15/6.1.
>>>> Those are the kernel versions used by Android, and Android TV in particular,
>>>> so it's kind of the way it goes for us.
>>>>
>>>>>
>>>>> Anyway, I need an ack from the ARM64 maintainers that this is ok to
>>>>> apply here before I can take it.
>>>>
>>>> Just out of curiosity, the change is pretty innocuous and simple to review,
>>>> why the extra scrutiny needed here?
>>>
>>> Why shouldn't the maintainers review a proposed backport patch for core
>>> kernel code that affects everyone who uses that arch?
>>
>> They should, but they are not, we can keep sending messages like those
>> in the hope that someone does, but clearly that is not working at the
>> moment.
>>
>> This patch cherry picked cleanly into 5.4 and 5.10 maybe they just trust
>> whoever submit stable bugfixes to have done their due diligence, too, I
>> don't know how to get that moving now but it fixes a real problem we
>> observed.
>>
> 
> FWIW, I understand why this might be useful when running under a
> non-KVM hypervisor that relies on memory hotplug to perform resource
> balancing between VMs. But the upshot of this change is that existing
> systems that do not rely on memory hotplug at all will suddenly lose
> any randomization of the linear map if its CPU happens to be able to
> address more than ~40 bits of physical memory. So I'm not convinced
> this is a change we should make for these older kernels.

Are there other patches that we could backport in order not to lose the 
randomization in the linear range?
-- 
Florian

Re: [PATCH stable 5.4] arm64: mm: account for hotplug memory when randomizing the linear region

[Greg KH]

On Wed, Jan 29, 2025 at 10:05:29AM -0800, Florian Fainelli wrote:
> On 1/12/25 03:53, Greg KH wrote:
> > On Thu, Jan 09, 2025 at 08:54:16AM -0800, Florian Fainelli wrote:
> > > From: Ard Biesheuvel <ardb@kernel.org>
> > > 
> > > commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> > > 
> > > As a hardening measure, we currently randomize the placement of
> > > physical memory inside the linear region when KASLR is in effect.
> > > Since the random offset at which to place the available physical
> > > memory inside the linear region is chosen early at boot, it is
> > > based on the memblock description of memory, which does not cover
> > > hotplug memory. The consequence of this is that the randomization
> > > offset may be chosen such that any hotplugged memory located above
> > > memblock_end_of_DRAM() that appears later is pushed off the end of
> > > the linear region, where it cannot be accessed.
> > > 
> > > So let's limit this randomization of the linear region to ensure
> > > that this can no longer happen, by using the CPU's addressable PA
> > > range instead. As it is guaranteed that no hotpluggable memory will
> > > appear that falls outside of that range, we can safely put this PA
> > > range sized window anywhere in the linear region.
> > > 
> > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> > > Cc: Will Deacon <will@kernel.org>
> > > Cc: Steven Price <steven.price@arm.com>
> > > Cc: Robin Murphy <robin.murphy@arm.com>
> > > Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> > > ---
> > >   arch/arm64/mm/init.c | 13 ++++++++-----
> > >   1 file changed, 8 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > > index cbcac03c0e0d..a6034645d6f7 100644
> > > --- a/arch/arm64/mm/init.c
> > > +++ b/arch/arm64/mm/init.c
> > > @@ -392,15 +392,18 @@ void __init arm64_memblock_init(void)
> > >   	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> > >   		extern u16 memstart_offset_seed;
> > > -		u64 range = linear_region_size -
> > > -			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
> > > +		u64 mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
> > > +		int parange = cpuid_feature_extract_unsigned_field(
> > > +					mmfr0, ID_AA64MMFR0_PARANGE_SHIFT);
> > > +		s64 range = linear_region_size -
> > > +			    BIT(id_aa64mmfr0_parange_to_phys_shift(parange));
> > >   		/*
> > >   		 * If the size of the linear region exceeds, by a sufficient
> > > -		 * margin, the size of the region that the available physical
> > > -		 * memory spans, randomize the linear region as well.
> > > +		 * margin, the size of the region that the physical memory can
> > > +		 * span, randomize the linear region as well.
> > >   		 */
> > > -		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> > > +		if (memstart_offset_seed > 0 && range >= (s64)ARM64_MEMSTART_ALIGN) {
> > >   			range /= ARM64_MEMSTART_ALIGN;
> > >   			memstart_addr -= ARM64_MEMSTART_ALIGN *
> > >   					 ((range * memstart_offset_seed) >> 16);
> > > -- 
> > > 2.43.0
> > > 
> > > 
> > 
> > You are not providing any information as to WHY this is needed in stable
> > kernels at all.  It just looks like an unsolicted backport with no
> > changes from upstream, yet no hint as to any bug it fixes.
> 
> See the response in the other thread.
> 
> > 
> > And you all really have hotpluggable memory on systems that are running
> > th is old kernel?  Why are they not using newer kernels if they need
> > this?  Surely lots of other bugs they need are resolved there, right?
> 
> Believe it or not, but memory hotplug works really well for us, in a
> somewhat limited configuration on the 5.4 kernel whereby we simply plug
> memory, and never unplug it thereafter, but still, we have not had to carry
> hotplug related patches other than this one.
> 
> Trying to be a good citizen here: one of my colleague has identified an
> upstream fix that works, that we got tested, cherry picked cleanly into both
> 5.4 and 5.10, so it's not even like there was any fuzz.
> 
> I was sort of hoping that giving my history of regularly testing stable
> kernels for the past years, as well as submitting a fair amount of targeted
> bug fixes to the stable branches that there would be some level of trust
> here.

Of course your history matters here, I'm not trying to disuade that at
all.  All I am saying is "this touches core arm64 code, so I would like
an arm64 maintainer to at least glance at it to say it's ok to do this."

And it looks like it now has happened, and it is good that I asked :)

This is all normal, and good, I'm not singling you out here at all.  We
push back on backports all the time when we don't understand why they
are being asked for and ask for a second review.  You want us to do this
in order to keep these trees working well.

thanks,

greg k-h

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Ard Biesheuvel]

On Thu, 30 Jan 2025 at 00:31, Florian Fainelli
<florian.fainelli@broadcom.com> wrote:
>
> On 1/29/25 14:15, Ard Biesheuvel wrote:
> > On Wed, 29 Jan 2025 at 18:45, Florian Fainelli
> > <florian.fainelli@broadcom.com> wrote:
> >>
> >> On 1/29/25 01:17, Greg KH wrote:
> >>> On Mon, Jan 20, 2025 at 08:33:12AM -0800, Florian Fainelli wrote:
> >>>>
> >>>>
> >>>> On 1/20/2025 5:59 AM, Greg KH wrote:
> >>>>> On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
> >>>>>>
> >>>>>>
> >>>>>> On 1/12/2025 3:54 AM, Greg KH wrote:
> >>>>>>> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
> >>>>>>>> On 1/9/25 08:54, Florian Fainelli wrote:
> >>>>>>>>> From: Ard Biesheuvel <ardb@kernel.org>
> >>>>>>>>>
> >>>>>>>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
> >>>>>>>>>
> >>>>>>>>> As a hardening measure, we currently randomize the placement of
> >>>>>>>>> physical memory inside the linear region when KASLR is in effect.
> >>>>>>>>> Since the random offset at which to place the available physical
> >>>>>>>>> memory inside the linear region is chosen early at boot, it is
> >>>>>>>>> based on the memblock description of memory, which does not cover
> >>>>>>>>> hotplug memory. The consequence of this is that the randomization
> >>>>>>>>> offset may be chosen such that any hotplugged memory located above
> >>>>>>>>> memblock_end_of_DRAM() that appears later is pushed off the end of
> >>>>>>>>> the linear region, where it cannot be accessed.
> >>>>>>>>>
> >>>>>>>>> So let's limit this randomization of the linear region to ensure
> >>>>>>>>> that this can no longer happen, by using the CPU's addressable PA
> >>>>>>>>> range instead. As it is guaranteed that no hotpluggable memory will
> >>>>>>>>> appear that falls outside of that range, we can safely put this PA
> >>>>>>>>> range sized window anywhere in the linear region.
> >>>>>>>>>
> >>>>>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >>>>>>>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> >>>>>>>>> Cc: Will Deacon <will@kernel.org>
> >>>>>>>>> Cc: Steven Price <steven.price@arm.com>
> >>>>>>>>> Cc: Robin Murphy <robin.murphy@arm.com>
> >>>>>>>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
> >>>>>>>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> >>>>>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> >>>>>>>>
> >>>>>>>> Forgot to update the patch subject, but this one is for 5.10.
> >>>>>>>
> >>>>>>> You also forgot to tell us _why_ this is needed :(
> >>>>>>
> >>>>>> This is explained in the second part of the first paragraph:
> >>>>>>
> >>>>>> The consequence of this is that the randomization offset may be chosen such
> >>>>>> that any hotplugged memory located above memblock_end_of_DRAM() that appears
> >>>>>> later is pushed off the end of the linear region, where it cannot be
> >>>>>> accessed.
> >>>>>>
> >>>>>> We use both memory hotplug and KASLR on our systems and that's how we
> >>>>>> eventually found out about the bug.
> >>>>>
> >>>>> And you still have 5.10.y ARM64 systems that need this?  Why not move to
> >>>>> a newer kernel version already?
> >>>>
> >>>> We still have ARM64 systems running 5.4 that need this, and the same bug
> >>>> applies to 5.10 that we used to support but dropped in favor of 5.15/6.1.
> >>>> Those are the kernel versions used by Android, and Android TV in particular,
> >>>> so it's kind of the way it goes for us.
> >>>>
> >>>>>
> >>>>> Anyway, I need an ack from the ARM64 maintainers that this is ok to
> >>>>> apply here before I can take it.
> >>>>
> >>>> Just out of curiosity, the change is pretty innocuous and simple to review,
> >>>> why the extra scrutiny needed here?
> >>>
> >>> Why shouldn't the maintainers review a proposed backport patch for core
> >>> kernel code that affects everyone who uses that arch?
> >>
> >> They should, but they are not, we can keep sending messages like those
> >> in the hope that someone does, but clearly that is not working at the
> >> moment.
> >>
> >> This patch cherry picked cleanly into 5.4 and 5.10 maybe they just trust
> >> whoever submit stable bugfixes to have done their due diligence, too, I
> >> don't know how to get that moving now but it fixes a real problem we
> >> observed.
> >>
> >
> > FWIW, I understand why this might be useful when running under a
> > non-KVM hypervisor that relies on memory hotplug to perform resource
> > balancing between VMs. But the upshot of this change is that existing
> > systems that do not rely on memory hotplug at all will suddenly lose
> > any randomization of the linear map if its CPU happens to be able to
> > address more than ~40 bits of physical memory. So I'm not convinced
> > this is a change we should make for these older kernels.
>
> Are there other patches that we could backport in order not to lose the
> randomization in the linear range?

No, this never got fixed. Only recently, I proposed some patches that
allow the PARange field in the CPU id registers to be overridden, and
this would also bring back the ability to randomize the linear map on
CPUs with a wide PARange.

Android also enables memory hotplug, and so I didn't bother with
preserving the old behavior when memory hotplug is disabled, and so
linear map randomization has basically been disabled ever since
(unless you are using an older core with only 40 physical address
bits).

Nobody ever complained about losing this linear map randomization, but
taking it away at this point from 5.4 and 5.10 goes a bit too far imo.

Re: [PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Florian Fainelli]

On 1/30/25 02:05, Ard Biesheuvel wrote:
> On Thu, 30 Jan 2025 at 00:31, Florian Fainelli
> <florian.fainelli@broadcom.com> wrote:
>>
>> On 1/29/25 14:15, Ard Biesheuvel wrote:
>>> On Wed, 29 Jan 2025 at 18:45, Florian Fainelli
>>> <florian.fainelli@broadcom.com> wrote:
>>>>
>>>> On 1/29/25 01:17, Greg KH wrote:
>>>>> On Mon, Jan 20, 2025 at 08:33:12AM -0800, Florian Fainelli wrote:
>>>>>>
>>>>>>
>>>>>> On 1/20/2025 5:59 AM, Greg KH wrote:
>>>>>>> On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 1/12/2025 3:54 AM, Greg KH wrote:
>>>>>>>>> On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:
>>>>>>>>>> On 1/9/25 08:54, Florian Fainelli wrote:
>>>>>>>>>>> From: Ard Biesheuvel <ardb@kernel.org>
>>>>>>>>>>>
>>>>>>>>>>> commit 97d6786e0669daa5c2f2d07a057f574e849dfd3e upstream
>>>>>>>>>>>
>>>>>>>>>>> As a hardening measure, we currently randomize the placement of
>>>>>>>>>>> physical memory inside the linear region when KASLR is in effect.
>>>>>>>>>>> Since the random offset at which to place the available physical
>>>>>>>>>>> memory inside the linear region is chosen early at boot, it is
>>>>>>>>>>> based on the memblock description of memory, which does not cover
>>>>>>>>>>> hotplug memory. The consequence of this is that the randomization
>>>>>>>>>>> offset may be chosen such that any hotplugged memory located above
>>>>>>>>>>> memblock_end_of_DRAM() that appears later is pushed off the end of
>>>>>>>>>>> the linear region, where it cannot be accessed.
>>>>>>>>>>>
>>>>>>>>>>> So let's limit this randomization of the linear region to ensure
>>>>>>>>>>> that this can no longer happen, by using the CPU's addressable PA
>>>>>>>>>>> range instead. As it is guaranteed that no hotpluggable memory will
>>>>>>>>>>> appear that falls outside of that range, we can safely put this PA
>>>>>>>>>>> range sized window anywhere in the linear region.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>>>>>>>>>>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>>>>>>>>>>> Cc: Will Deacon <will@kernel.org>
>>>>>>>>>>> Cc: Steven Price <steven.price@arm.com>
>>>>>>>>>>> Cc: Robin Murphy <robin.murphy@arm.com>
>>>>>>>>>>> Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@kernel.org
>>>>>>>>>>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>>>>>>>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>>>>>>>>>>
>>>>>>>>>> Forgot to update the patch subject, but this one is for 5.10.
>>>>>>>>>
>>>>>>>>> You also forgot to tell us _why_ this is needed :(
>>>>>>>>
>>>>>>>> This is explained in the second part of the first paragraph:
>>>>>>>>
>>>>>>>> The consequence of this is that the randomization offset may be chosen such
>>>>>>>> that any hotplugged memory located above memblock_end_of_DRAM() that appears
>>>>>>>> later is pushed off the end of the linear region, where it cannot be
>>>>>>>> accessed.
>>>>>>>>
>>>>>>>> We use both memory hotplug and KASLR on our systems and that's how we
>>>>>>>> eventually found out about the bug.
>>>>>>>
>>>>>>> And you still have 5.10.y ARM64 systems that need this?  Why not move to
>>>>>>> a newer kernel version already?
>>>>>>
>>>>>> We still have ARM64 systems running 5.4 that need this, and the same bug
>>>>>> applies to 5.10 that we used to support but dropped in favor of 5.15/6.1.
>>>>>> Those are the kernel versions used by Android, and Android TV in particular,
>>>>>> so it's kind of the way it goes for us.
>>>>>>
>>>>>>>
>>>>>>> Anyway, I need an ack from the ARM64 maintainers that this is ok to
>>>>>>> apply here before I can take it.
>>>>>>
>>>>>> Just out of curiosity, the change is pretty innocuous and simple to review,
>>>>>> why the extra scrutiny needed here?
>>>>>
>>>>> Why shouldn't the maintainers review a proposed backport patch for core
>>>>> kernel code that affects everyone who uses that arch?
>>>>
>>>> They should, but they are not, we can keep sending messages like those
>>>> in the hope that someone does, but clearly that is not working at the
>>>> moment.
>>>>
>>>> This patch cherry picked cleanly into 5.4 and 5.10 maybe they just trust
>>>> whoever submit stable bugfixes to have done their due diligence, too, I
>>>> don't know how to get that moving now but it fixes a real problem we
>>>> observed.
>>>>
>>>
>>> FWIW, I understand why this might be useful when running under a
>>> non-KVM hypervisor that relies on memory hotplug to perform resource
>>> balancing between VMs. But the upshot of this change is that existing
>>> systems that do not rely on memory hotplug at all will suddenly lose
>>> any randomization of the linear map if its CPU happens to be able to
>>> address more than ~40 bits of physical memory. So I'm not convinced
>>> this is a change we should make for these older kernels.
>>
>> Are there other patches that we could backport in order not to lose the
>> randomization in the linear range?
> 
> No, this never got fixed. Only recently, I proposed some patches that
> allow the PARange field in the CPU id registers to be overridden, and
> this would also bring back the ability to randomize the linear map on
> CPUs with a wide PARange.
> 
> Android also enables memory hotplug, and so I didn't bother with
> preserving the old behavior when memory hotplug is disabled, and so
> linear map randomization has basically been disabled ever since
> (unless you are using an older core with only 40 physical address
> bits).

We are using Brahma-B53 cores with 5.4 primarily which are 
architecturally equivalent to a Cortex-A53 where 
ID_AA64MMFR0_EL1.PARange = 0b0010 -> 40 bits only. The other platform 
that we use has a Cortex-A72 that supports up to 44 bits of PA, but that 
one could probably get a custom kernel with memory hotplug disabled.

> 
> Nobody ever complained about losing this linear map randomization, but
> taking it away at this point from 5.4 and 5.10 goes a bit too far imo.

Fair enough thanks for the background!
-- 
Florian