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fork: Add generic vmalloced stack support

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If CONFIG_VMAP_STACK=y is selected, kernel stacks are allocated with
__vmalloc_node_range().

Grsecurity has had a similar feature (called GRKERNSEC_KSTACKOVERFLOW=y)
for a long time.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/14c07d4fd173a5b117f51e8b939f9f4323e39899.1470907718.git.luto@kernel.org
[ Minor edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2016-08-11 02:35:21 -07:00 committed by Ingo Molnar
parent eb4e841099
commit ba14a194a4
4 changed files with 126 additions and 21 deletions
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34
arch/Kconfig
View file

@ -707,4 +707,38 @@ 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
default y
bool "Use a virtually-mapped stack"
depends on HAVE_ARCH_VMAP_STACK && !KASAN
---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.
This is presently incompatible with KASAN because KASAN expects
the stack to map directly to the KASAN shadow map using a formula
that is incorrect if the stack is in vmalloc space.
source "kernel/gcov/Kconfig"

2
arch/ia64/include/asm/thread_info.h
View file

@ -56,7 +56,7 @@ struct thread_info {
#define alloc_thread_stack_node(tsk, node) ((unsigned long *) 0)
#define task_thread_info(tsk) ((struct thread_info *) 0)
#endif
#define free_thread_stack(ti) /* nothing */
#define free_thread_stack(tsk) /* nothing */
#define task_stack_page(tsk) ((void *)(tsk))
#define __HAVE_THREAD_FUNCTIONS

15
include/linux/sched.h
View file

@ -1923,6 +1923,9 @@ 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;
/*
@ -1939,6 +1942,18 @@ 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)

96
kernel/fork.c
View file

@ -158,19 +158,39 @@ 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));
/*
* We can't call find_vm_area() in interrupt context, and
* free_thread_stack() can be called in interrupt context,
* so cache the vm_struct.
*/
if (stack)
tsk->stack_vm_area = find_vm_area(stack);
return stack;
#else
struct page *page = alloc_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_pages(virt_to_page(stack), THREAD_SIZE_ORDER);
if (task_stack_vm_area(tsk))
vfree(tsk->stack);
else
__free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER);
}
# else
static struct kmem_cache *thread_stack_cache;
@ -181,9 +201,9 @@ 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 +233,47 @@ 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(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);
mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
THREAD_SIZE / 1024 * account);
BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
memcg_kmem_update_page_stat(
first_page, MEMCG_KERNEL_STACK_KB,
account * (THREAD_SIZE / 1024));
if (vm) {
int i;
BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
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 {
/*
* 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));
}
}
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);
@ -342,6 +385,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
{
struct task_struct *tsk;
unsigned long *stack;
struct vm_struct *stack_vm_area;
int err;
if (node == NUMA_NO_NODE)
@ -354,11 +398,23 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
if (!stack)
goto free_tsk;
stack_vm_area = task_stack_vm_area(tsk);
err = arch_dup_task_struct(tsk, orig);
/*
* arch_dup_task_struct() clobbers the stack-related fields. Make
* sure they're properly initialized before using any stack-related
* functions again.
*/
tsk->stack = stack;
#ifdef CONFIG_VMAP_STACK
tsk->stack_vm_area = stack_vm_area;
#endif
if (err)
goto free_stack;
tsk->stack = stack;
#ifdef CONFIG_SECCOMP
/*
* We must handle setting up seccomp filters once we're under
@ -390,14 +446,14 @@ 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(stack, 1);
account_kernel_stack(tsk, 1);
kcov_task_init(tsk);
return tsk;
free_stack:
free_thread_stack(stack);
free_thread_stack(tsk);
free_tsk:
free_task_struct(tsk);
return NULL;