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@xxxxxxxxxx> > > > > > > > > > > > > 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@xxxxxxxxxx> > > > > > > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> > > > > > > Cc: Will Deacon <will@xxxxxxxxxx> > > > > > > Cc: Steven Price <steven.price@xxxxxxx> > > > > > > Cc: Robin Murphy <robin.murphy@xxxxxxx> > > > > > > Link: https://lore.kernel.org/r/20201014081857.3288-1-ardb@xxxxxxxxxx > > > > > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > > > > > Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx> > > > > > > > > > > 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
