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 <dave@nullcore.net>
[kees: adjust commit log, split patch, provide usage trace]
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Rik van Riel <riel@redhat.com>
This commit is contained in:
David Windsor 2017-06-10 22:50:41 -04:00 коммит произвёл Kees Cook
Родитель 07dcd7fe89
Коммит f9d29946c5
1 изменённых файлов: 3 добавлений и 2 удалений

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@ -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