From c031a4213c11a5db475f528c182f7b3858df11db Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Fri, 29 Jan 2016 11:59:03 +0100 Subject: [PATCH] arm64: kaslr: randomize the linear region When KASLR is enabled (CONFIG_RANDOMIZE_BASE=y), and entropy has been provided by the bootloader, randomize the placement of RAM inside the linear region if sufficient space is available. For instance, on a 4KB granule/3 levels kernel, the linear region is 256 GB in size, and we can choose any 1 GB aligned offset that is far enough from the top of the address space to fit the distance between the start of the lowest memblock and the top of the highest memblock. Signed-off-by: Ard Biesheuvel Signed-off-by: Catalin Marinas --- arch/arm64/kernel/kaslr.c | 4 ++++ arch/arm64/mm/init.c | 22 ++++++++++++++++++++-- 2 files changed, 24 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c index 8b32a1f8f09f..582983920054 100644 --- a/arch/arm64/kernel/kaslr.c +++ b/arch/arm64/kernel/kaslr.c @@ -21,6 +21,7 @@ #include u64 __read_mostly module_alloc_base; +u16 __initdata memstart_offset_seed; static __init u64 get_kaslr_seed(void *fdt) { @@ -123,6 +124,9 @@ u64 __init kaslr_early_init(u64 dt_phys) mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1); offset = seed & mask; + /* use the top 16 bits to randomize the linear region */ + memstart_offset_seed = seed >> 48; + /* * The kernel Image should not extend across a 1GB/32MB/512MB alignment * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index c0ea54bd9995..e1f425fe5a81 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -196,6 +196,23 @@ void __init arm64_memblock_init(void) memblock_add(__pa(_text), (u64)(_end - _text)); } + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) { + extern u16 memstart_offset_seed; + u64 range = linear_region_size - + (memblock_end_of_DRAM() - memblock_start_of_DRAM()); + + /* + * 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. + */ + if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) { + range = range / ARM64_MEMSTART_ALIGN + 1; + memstart_addr -= ARM64_MEMSTART_ALIGN * + ((range * memstart_offset_seed) >> 16); + } + } + /* * Register the kernel text, kernel data, initrd, and initial * pagetables with memblock. @@ -365,12 +382,13 @@ void __init mem_init(void) #ifdef CONFIG_SPARSEMEM_VMEMMAP MLG((unsigned long)vmemmap, (unsigned long)vmemmap + VMEMMAP_SIZE), - MLM((unsigned long)virt_to_page(PAGE_OFFSET), + MLM((unsigned long)phys_to_page(memblock_start_of_DRAM()), (unsigned long)virt_to_page(high_memory)), #endif MLK(FIXADDR_START, FIXADDR_TOP), MLM(PCI_IO_START, PCI_IO_END), - MLM(PAGE_OFFSET, (unsigned long)high_memory)); + MLM(__phys_to_virt(memblock_start_of_DRAM()), + (unsigned long)high_memory)); #undef MLK #undef MLM -- 2.39.2