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);