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Date: Fri, 1 Jul 2016 16:59:20 +0200
From: Borislav Petkov <bp@...en8.de>
To: Andy Lutomirski <luto@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v4 09/29] fork: Add generic vmalloced stack support
On Sun, Jun 26, 2016 at 02:55:31PM -0700, Andy Lutomirski wrote:
> If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with
> vmalloc_node.
>
> grsecurity has had a similar feature (called
> GRKERNSEC_KSTACKOVERFLOW) for a long time.
>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
> arch/Kconfig | 29 +++++++++++++
> arch/ia64/include/asm/thread_info.h | 2 +-
> include/linux/sched.h | 15 +++++++
> kernel/fork.c | 87 +++++++++++++++++++++++++++++--------
> 4 files changed, 113 insertions(+), 20 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 15996290fed4..18a2c3a7b460 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -661,4 +661,33 @@ config ARCH_NO_COHERENT_DMA_MMAP
> config CPU_NO_EFFICIENT_FFS
> def_bool n
>
> +config HAVE_ARCH_VMAP_STACK
> + def_bool n
> + help
> + An arch should select this symbol if it can support kernel stacks
> + in vmalloc space. This means:
> +
> + - vmalloc space must be large enough to hold many kernel stacks.
> + This may rule out many 32-bit architectures.
> +
> + - Stacks in vmalloc space need to work reliably. For example, if
> + vmap page tables are created on demand, either this mechanism
> + needs to work while the stack points to a virtual address with
> + unpopulated page tables or arch code (switch_to and switch_mm,
> + most likely) needs to ensure that the stack's page table entries
> + are populated before running on a possibly unpopulated stack.
> +
> + - If the stack overflows into a guard page, something reasonable
> + should happen. The definition of "reasonable" is flexible, but
> + instantly rebooting without logging anything would be unfriendly.
Nice, I wish more people would actually *explain* their Kconfig options
properly.
...
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 146c9840c079..06761de69360 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -158,19 +158,37 @@ void __weak arch_release_thread_stack(unsigned long *stack)
> * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
> * kmemcache based allocator.
> */
> -# if THREAD_SIZE >= PAGE_SIZE
> -static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
> - int node)
> +# if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)
> +static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
> {
> +#ifdef CONFIG_VMAP_STACK
> + void *stack = __vmalloc_node_range(
> + THREAD_SIZE, THREAD_SIZE, VMALLOC_START, VMALLOC_END,
> + THREADINFO_GFP | __GFP_HIGHMEM, PAGE_KERNEL,
> + 0, node, __builtin_return_address(0));
Reformat:
void *stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE,
VMALLOC_START, VMALLOC_END,
THREADINFO_GFP | __GFP_HIGHMEM,
PAGE_KERNEL,
0, node, __builtin_return_address(0));
> +
> + /*
> + * We can't call find_vm_area() in interrupt context, and
> + * free_thread_info can be called in interrupt context, so cache
free_thread_stack() ?
> + * the vm_struct.
> + */
> + if (stack)
> + tsk->stack_vm_area = find_vm_area(stack);
> + return stack;
> +#else
> struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
> THREAD_SIZE_ORDER);
>
> return page ? page_address(page) : NULL;
> +#endif
> }
>
> -static inline void free_thread_stack(unsigned long *stack)
> +static inline void free_thread_stack(struct task_struct *tsk)
> {
> - free_kmem_pages((unsigned long)stack, THREAD_SIZE_ORDER);
> + if (task_stack_vm_area(tsk))
> + vfree(tsk->stack);
> + else
> + free_kmem_pages((unsigned long)tsk->stack, THREAD_SIZE_ORDER);
> }
> # else
> static struct kmem_cache *thread_stack_cache;
> @@ -181,9 +199,9 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
> return kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
> }
>
> -static void free_thread_stack(unsigned long *stack)
> +static void free_thread_stack(struct task_struct *tsk)
> {
> - kmem_cache_free(thread_stack_cache, stack);
> + kmem_cache_free(thread_stack_cache, tsk->stack);
> }
>
> void thread_stack_cache_init(void)
> @@ -213,24 +231,49 @@ struct kmem_cache *vm_area_cachep;
> /* SLAB cache for mm_struct structures (tsk->mm) */
> static struct kmem_cache *mm_cachep;
>
> -static void account_kernel_stack(unsigned long *stack, int account)
> +static void account_kernel_stack(struct task_struct *tsk, int account)
> {
> - /* All stack pages are in the same zone and belong to the same memcg. */
> - struct page *first_page = virt_to_page(stack);
> + void *stack = task_stack_page(tsk);
> + struct vm_struct *vm = task_stack_vm_area(tsk);
> +
> + BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
> +
> + if (vm) {
> + int i;
>
> - mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
> - THREAD_SIZE / 1024 * account);
> + BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
>
> - memcg_kmem_update_page_stat(
> - first_page, MEMCG_KERNEL_STACK_KB,
> - account * (THREAD_SIZE / 1024));
> + for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> + mod_zone_page_state(page_zone(vm->pages[i]),
> + NR_KERNEL_STACK_KB,
> + PAGE_SIZE / 1024 * account);
> + }
> +
> + /* All stack pages belong to the same memcg. */
> + memcg_kmem_update_page_stat(
> + vm->pages[0], MEMCG_KERNEL_STACK_KB,
> + account * (THREAD_SIZE / 1024));
Formatting:
function_name(arg0, arg1,
arg2, arg3, ...);
> + } else {
> + /*
> + * All stack pages are in the same zone and belong to the
> + * same memcg.
> + */
> + struct page *first_page = virt_to_page(stack);
> +
> + mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
> + THREAD_SIZE / 1024 * account);
> +
> + memcg_kmem_update_page_stat(
> + first_page, MEMCG_KERNEL_STACK_KB,
> + account * (THREAD_SIZE / 1024));
Ditto.
> + }
> }
>
> void free_task(struct task_struct *tsk)
> {
> - account_kernel_stack(tsk->stack, -1);
> + account_kernel_stack(tsk, -1);
> arch_release_thread_stack(tsk->stack);
> - free_thread_stack(tsk->stack);
> + free_thread_stack(tsk);
> rt_mutex_debug_task_free(tsk);
> ftrace_graph_exit_task(tsk);
> put_seccomp_filter(tsk);
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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