From f9d29946c56734e954459bc9a0e688a8ae9b4cbf Mon Sep 17 00:00:00 2001 From: David Windsor Date: Sat, 10 Jun 2017 22:50:41 -0400 Subject: fork: Define usercopy region in thread_stack slab caches In support of usercopy hardening, this patch defines a region in the thread_stack slab caches in which userspace copy operations are allowed. Since the entire thread_stack needs to be available to userspace, the entire slab contents are whitelisted. Note that the slab-based thread stack is only present on systems with THREAD_SIZE < PAGE_SIZE and !CONFIG_VMAP_STACK. cache object allocation: kernel/fork.c: alloc_thread_stack_node(...): return kmem_cache_alloc_node(thread_stack_cache, ...) dup_task_struct(...): ... stack = alloc_thread_stack_node(...) ... tsk->stack = stack; copy_process(...): ... dup_task_struct(...) _do_fork(...): ... copy_process(...) This region is known as the slab cache's usercopy region. Slab caches can now check that each dynamically sized copy operation involving cache-managed memory falls entirely within the slab's usercopy region. This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY whitelisting code in the last public patch of grsecurity/PaX based on my understanding of the code. Changes or omissions from the original code are mine and don't reflect the original grsecurity/PaX code. Signed-off-by: David Windsor [kees: adjust commit log, split patch, provide usage trace] Cc: Ingo Molnar Cc: Andrew Morton Cc: Thomas Gleixner Cc: Andy Lutomirski Signed-off-by: Kees Cook Acked-by: Rik van Riel --- kernel/fork.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'kernel/fork.c') diff --git a/kernel/fork.c b/kernel/fork.c index 82f2a0441d3b..0e086af148f2 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -282,8 +282,9 @@ static void free_thread_stack(struct task_struct *tsk) void thread_stack_cache_init(void) { - thread_stack_cache = kmem_cache_create("thread_stack", THREAD_SIZE, - THREAD_SIZE, 0, NULL); + thread_stack_cache = kmem_cache_create_usercopy("thread_stack", + THREAD_SIZE, THREAD_SIZE, 0, 0, + THREAD_SIZE, NULL); BUG_ON(thread_stack_cache == NULL); } # endif -- cgit v1.2.3