Messages in this thread | | | From | Kees Cook <> | Date | Tue, 21 Jun 2016 10:13:14 -0700 | Subject | Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support |
| |
On Tue, Jun 21, 2016 at 9:59 AM, Andy Lutomirski <luto@amacapital.net> wrote: > On Tue, Jun 21, 2016 at 12:30 AM, Jann Horn <jannh@google.com> wrote: >> On Tue, Jun 21, 2016 at 1:43 AM, Andy Lutomirski <luto@kernel.org> wrote: >>> If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with >>> vmalloc_node. >> [...] >>> static struct thread_info *alloc_thread_info_node(struct task_struct *tsk, >>> int node) >>> { >>> +#ifdef CONFIG_VMAP_STACK >>> + struct thread_info *ti = __vmalloc_node_range( >>> + THREAD_SIZE, THREAD_SIZE, VMALLOC_START, VMALLOC_END, >>> + THREADINFO_GFP | __GFP_HIGHMEM, PAGE_KERNEL, >>> + 0, node, __builtin_return_address(0)); >>> + >> >> After spender gave some hints on IRC about the guard pages not working >> reliably, I decided to have a closer look at this. As far as I can >> tell, the idea is that __vmalloc_node_range() automatically adds guard >> pages unless the VM_NO_GUARD flag is specified. However, those guard >> pages are *behind* allocations, not in front of them, while a stack >> guard primarily needs to be in front of the allocation. This wouldn't >> matter if all allocations in the vmalloc area had guard pages behind >> them, but if someone first does some data allocation with VM_NO_GUARD >> and then a stack allocation directly behind that, there won't be a >> guard between the data allocation and the stack allocation. > > I'm tempted to explicitly disallow VM_NO_GUARD in the vmalloc range. > It has no in-tree users for non-fixed addresses right now.
What about the lack of pre-range guard page? That seems like a critical feature for this. :)
-Kees
-- Kees Cook Chrome OS & Brillo Security
| |