On Mon, Jul 11, 2016 at 11:57 AM, Andrey Ryabinin <aryabi...@virtuozzo.com> wrote: > > > On 07/10/2016 03:47 PM, Andy Lutomirski wrote: >> Hi all- >> >> I found two nasty issues with virtually mapped stacks if KASAN is >> enabled. The first issue is a crash: the first non-init stack is >> allocated and accessed before KASAN initializes its zero shadow >> AFAICT, which means that we switch to that stack and then blow up when >> we start recursively faulting on failed accesses to the shadow. >> > > KASAN initialized quite early, before any non-init task exists. The crash > happens > because non-init task writes to write-protected zero shadow. > Currently KASAN doesn't allocate shadow memory for vmalloc addresses, we just > map single > zero page and write protect it. > > >> The second issue is that, even if we survive (we initialize the zero >> shadow on time), KASAN will fail to protect hte stack. >> >> For now, I just disabled use of virtually mapped stacks if KASAN is >> on. Do you have any easy ideas to fix it? >> > > Allocate shadow memory which backs vmalloc/vmap allocations is the only way > to fix this. > I can do this, and post the patches soon enough.
Do you want to allocate it eagerly? Won't it consume 1/8 of vmalloc range worth of physical memory?