On Mon, Jan 13, 2025 at 07:44:50AM -0800, Florian Fainelli wrote:

On 1/12/2025 3:54 AM, Greg KH wrote:

quoted

On Thu, Jan 09, 2025 at 09:01:13AM -0800, Florian Fainelli wrote:

quoted

On 1/9/25 08:54, Florian Fainelli wrote:

quoted

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 <redacted>
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 (local)
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