Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH 30/38] fork: Define usercopy region in thread_stack slab caches | Date | Wed, 10 Jan 2018 18:03:02 -0800 |
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From: David Windsor <dave@nullcore.net>
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> --- kernel/fork.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
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 -- 2.7.4
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