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@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>
---
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
