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Message-ID: <20160620133614.GE9892@dhcp22.suse.cz>
Date: Mon, 20 Jun 2016 15:36:14 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Andy Lutomirski <luto@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
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>
Subject: Re: [PATCH v2 06/13] fork: Add generic vmalloced stack support
On Fri 17-06-16 13:00:42, Andy Lutomirski wrote:
> If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with
> vmalloc_node.
I like this! It also reduces demand for higher order (order-2) pages
considerably which is a great plus on its own. I would be little bit
worried about the performance because vmalloc wasn't the fastest one
AFAIR. Have you tried to measure that?
>From a quick glance the patch looks OK, I will have to look closer
though.
> 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 | 81 +++++++++++++++++++++++++++++--------
> 4 files changed, 109 insertions(+), 18 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index d794384a0404..a71e6e7195e6 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -658,4 +658,33 @@ 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.
> +
> +config VMAP_STACK
> + bool "Use a virtually-mapped stack"
> + depends on HAVE_ARCH_VMAP_STACK
> + ---help---
> + Enable this if you want the use virtually-mapped kernel stacks
> + with guard pages. This causes kernel stack overflows to be
> + caught immediately rather than causing difficult-to-diagnose
> + corruption.
> +
> source "kernel/gcov/Kconfig"
> diff --git a/arch/ia64/include/asm/thread_info.h b/arch/ia64/include/asm/thread_info.h
> index aa995b67c3f5..d13edda6e09c 100644
> --- a/arch/ia64/include/asm/thread_info.h
> +++ b/arch/ia64/include/asm/thread_info.h
> @@ -56,7 +56,7 @@ struct thread_info {
> #define alloc_thread_info_node(tsk, node) ((struct thread_info *) 0)
> #define task_thread_info(tsk) ((struct thread_info *) 0)
> #endif
> -#define free_thread_info(ti) /* nothing */
> +#define free_thread_info(tsk) /* nothing */
> #define task_stack_page(tsk) ((void *)(tsk))
>
> #define __HAVE_THREAD_FUNCTIONS
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6e42ada26345..a37c3b790309 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1918,6 +1918,9 @@ struct task_struct {
> #ifdef CONFIG_MMU
> struct task_struct *oom_reaper_list;
> #endif
> +#ifdef CONFIG_VMAP_STACK
> + struct vm_struct *stack_vm_area;
> +#endif
> /* CPU-specific state of this task */
> struct thread_struct thread;
> /*
> @@ -1934,6 +1937,18 @@ extern int arch_task_struct_size __read_mostly;
> # define arch_task_struct_size (sizeof(struct task_struct))
> #endif
>
> +#ifdef CONFIG_VMAP_STACK
> +static inline struct vm_struct *task_stack_vm_area(const struct task_struct *t)
> +{
> + return t->stack_vm_area;
> +}
> +#else
> +static inline struct vm_struct *task_stack_vm_area(const struct task_struct *t)
> +{
> + return NULL;
> +}
> +#endif
> +
> /* Future-safe accessor for struct task_struct's cpus_allowed. */
> #define tsk_cpus_allowed(tsk) (&(tsk)->cpus_allowed)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index cd2abe6e4e41..ad77a6b07708 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -158,19 +158,38 @@ void __weak arch_release_thread_info(struct thread_info *ti)
> * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
> * kmemcache based allocator.
> */
> -# if THREAD_SIZE >= PAGE_SIZE
> +# if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)
> 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));
> +
> + /*
> + * We can't call find_vm_area() in interrupt context, and
> + * free_thread_info can be called in interrupt context, so cache
> + * the vm_struct.
> + */
> + if (ti)
> + tsk->stack_vm_area = find_vm_area(ti);
> + return ti;
> +#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_info(struct thread_info *ti)
> +static inline void free_thread_info(struct task_struct *tsk)
> {
> - free_kmem_pages((unsigned long)ti, 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_info_cache;
> @@ -181,9 +200,9 @@ static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
> return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
> }
>
> -static void free_thread_info(struct thread_info *ti)
> +static void free_thread_info(struct task_struct *tsk)
> {
> - kmem_cache_free(thread_info_cache, ti);
> + kmem_cache_free(thread_info_cache, tsk->stack);
> }
>
> void thread_info_cache_init(void)
> @@ -213,24 +232,46 @@ 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(struct thread_info *ti, int account)
> +static void account_kernel_stack(struct task_struct *tsk, int account)
> {
> - struct zone *zone = page_zone(virt_to_page(ti));
> + struct zone *zone;
> + struct thread_info *ti = task_thread_info(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(zone, NR_KERNEL_STACK_KB,
> - THREAD_SIZE / 1024 * account);
> + BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
>
> - /* All stack pages belong to the same memcg. */
> - memcg_kmem_update_page_stat(
> - virt_to_page(ti), MEMCG_KERNEL_STACK,
> - account * (THREAD_SIZE / PAGE_SIZE));
> + for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> + mod_zone_page_state(page_zone(vm->pages[i]),
> + 1, PAGE_SIZE / 1024 * account);
> + }
> +
> + /* All stack pages belong to the same memcg. */
> + memcg_kmem_update_page_stat(
> + vm->pages[0], MEMCG_KERNEL_STACK,
> + account * (THREAD_SIZE / PAGE_SIZE));
> + } else {
> + zone = page_zone(virt_to_page(ti));
> +
> + mod_zone_page_state(zone, NR_KERNEL_STACK_KB,
> + THREAD_SIZE / 1024 * account);
> +
> + /* All stack pages belong to the same memcg. */
> + memcg_kmem_update_page_stat(
> + virt_to_page(ti), MEMCG_KERNEL_STACK,
> + account * (THREAD_SIZE / PAGE_SIZE));
> + }
> }
>
> void free_task(struct task_struct *tsk)
> {
> - account_kernel_stack(tsk->stack, -1);
> + account_kernel_stack(tsk, -1);
> arch_release_thread_info(tsk->stack);
> - free_thread_info(tsk->stack);
> + free_thread_info(tsk);
> rt_mutex_debug_task_free(tsk);
> ftrace_graph_exit_task(tsk);
> put_seccomp_filter(tsk);
> @@ -342,6 +383,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> {
> struct task_struct *tsk;
> struct thread_info *ti;
> + struct vm_struct *stack_vm_area;
> int err;
>
> if (node == NUMA_NO_NODE)
> @@ -354,11 +396,16 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> if (!ti)
> goto free_tsk;
>
> + stack_vm_area = task_stack_vm_area(tsk);
> +
> err = arch_dup_task_struct(tsk, orig);
> if (err)
> goto free_ti;
>
> tsk->stack = ti;
> +#ifdef CONFIG_VMAP_STACK
> + tsk->stack_vm_area = stack_vm_area;
> +#endif
> #ifdef CONFIG_SECCOMP
> /*
> * We must handle setting up seccomp filters once we're under
> @@ -390,14 +437,14 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> tsk->task_frag.page = NULL;
> tsk->wake_q.next = NULL;
>
> - account_kernel_stack(ti, 1);
> + account_kernel_stack(tsk, 1);
>
> kcov_task_init(tsk);
>
> return tsk;
>
> free_ti:
> - free_thread_info(ti);
> + free_thread_info(tsk);
> free_tsk:
> free_task_struct(tsk);
> return NULL;
> --
> 2.5.5
--
Michal Hocko
SUSE Labs
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