On 05/08/19 at 04:04pm, Baoquan He wrote: > 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. > > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx> > Acked-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> I think this's worth noticing stable tree: Cc: stable@xxxxxxxxxxxxxxx > --- > 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++) > -- > 2.17.2 >
