On Sat, Feb 16, 2019 at 6:04 AM Baoquan He <b...@redhat.com> wrote: > > Vmemmap region has different maximum size depending on paging mode. > Now its size is hardcoded as 1TB in memory KASLR, this is not > right for 5-level paging mode. It will cause overflow if vmemmap > region is randomized to be adjacent to cpu_entry_area region and > its actual size is bigger than 1TB. > > So here calculate how many TB by the actual size of vmemmap region > and align up to 1TB boundary. > > Signed-off-by: Baoquan He <b...@redhat.com> > --- > 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 97768df923e3..ca12ed4e5239 100644 > --- a/arch/x86/mm/kaslr.c > +++ b/arch/x86/mm/kaslr.c > @@ -101,7 +101,7 @@ static __initdata struct kaslr_memory_region { > } kaslr_regions[] = { > { &page_offset_base, 0 }, > { &vmalloc_base, 0 }, > - { &vmemmap_base, 1 }, > + { &vmemmap_base, 0 }, > }; > > /* > @@ -121,6 +121,7 @@ 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; > @@ -152,6 +153,14 @@ 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 align to > + * 1TB boundary.
Can you describe why this is the right calculation? (This will help explain why 4-level is different from 5-level here.) > + */ > + 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++) > -- > 2.17.2 > Otherwise, yeah, looks great! -- Kees Cook