fork: Add generic vmalloced stack support

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>

diff --git a/arch/Kconfig b/arch/Kconfig
index e9c9334..9ecf9f6 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -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"

diff --git a/arch/ia64/include/asm/thread_info.h b/arch/ia64/include/asm/thread_info.h
index 29bd597..c702642 100644 (file)
--- 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_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

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 62c68e5..20f9f47 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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)
 

diff --git a/kernel/fork.c b/kernel/fork.c
index 52e725d..9b85f6b 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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);
+
+       BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
+
+       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);
+               }
 
-       mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
-                           THREAD_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));
+               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;