kernel_randomize_memory() hardcodes the size of vmemmap section as 1 TB, to support the maximum amount of system RAM in 4-level paging mode, 64 TB.
However, 1 TB is not enough for vmemmap in 5-level paging mode. Assuming the size of struct page is 64 Bytes, to support 4 PB system RAM in 5-level, 64 TB of vmemmap area is needed. The wrong hardcoding may cause vmemmap stamping into the following cpu_entry_area section, if KASLR puts vmemmap very close to cpu_entry_area , and the actual area of vmemmap is much bigger than 1 TB.
So here calculate the actual size of vmemmap region, then align up to 1 TB boundary. In 4-level it's always 1 TB. In 5-level it's adjusted on demand. The current code reserves 0.5 PB for vmemmap in 5-level. In this new way, the left space can be saved to join randomization to increase the entropy.
Fiexes: eedb92abb9bb ("x86/mm: Make virtual memory layout dynamic for CONFIG_X86_5LEVEL=y") Signed-off-by: Baoquan He bhe@redhat.com Acked-by: Kirill A. Shutemov kirill@linux.intel.com Reviewed-by: Kees Cook keescook@chromium.org Cc: stable@vger.kernel.org --- v4->v5: Add Fixes tag and Cc to stable. v3->v4: Fix the incorrect style of code comment; Add ack tags from Kirill and Kees. v3 discussion is here: http://lkml.kernel.org/r/20190422091045.GB3584@localhost.localdomain arch/x86/mm/kaslr.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index dc3f058bdf9b..c0eedb85a92f 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_region { } kaslr_regions[] = { { &page_offset_base, 0 }, { &vmalloc_base, 0 }, - { &vmemmap_base, 1 }, + { &vmemmap_base, 0 }, };
/* Get size in bytes used by the memory region */ @@ -78,6 +78,7 @@ void __init kernel_randomize_memory(void) unsigned long rand, memory_tb; struct rnd_state rand_state; unsigned long remain_entropy; + unsigned long vmemmap_size;
vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4; vaddr = vaddr_start; @@ -109,6 +110,14 @@ void __init kernel_randomize_memory(void) if (memory_tb < kaslr_regions[0].size_tb) kaslr_regions[0].size_tb = memory_tb;
+ /* + * Calculate how many TB vmemmap region needs, and aligned to + * 1TB boundary. + */ + vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) * + sizeof(struct page); + kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT); + /* Calculate entropy available between regions */ remain_entropy = vaddr_end - vaddr_start; for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)