[PATCH v3 06/13] fork: Add generic vmalloced stack support

Andy Lutomirski
2016-06-20T23:45:15Z

If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with
vmalloc_node.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/Kconfig | 29 +++++++++++++
arch/ia64/include/asm/thread_info.h | 2 +-
include/linux/sched.h | 15 +++++++
kernel/fork.c | 82 +++++++++++++++++++++++++++++--------
4 files changed, 110 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 ff3c41c2ba96..fe1c785e5f8c 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 +232,47 @@ 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_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));
+ } 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_KB,
+ account * (THREAD_SIZE / 1024));
+ }
}

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 +384,7 @@ 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 +397,16 @@ 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 +438,14 @@ 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