Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 30 Jan 2017 14:19:07 -0800
From: Kees Cook <keescook@...omium.org>
To: Keun-O Park <kpark3469@...il.com>
Cc: AKASHI Takahiro <takahiro.akashi@...aro.org>, Will Deacon <will.deacon@....com>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, 
	James Morse <james.morse@....com>, Pratyush Anand <panand@...hat.com>, keun-o.park@...kmatter.ae
Subject: Re: [PATCH] arm64: usercopy: Implement stack frame object validation

On Mon, Jan 30, 2017 at 4:42 AM, Keun-O Park <kpark3469@...il.com> wrote:
> Thanks so much for the example code. Basically I totally missed this case.
> I modified do_usercopy_stack() slightly following your code snippet.
> Like your comment, I could see the similar result.
> ....
>         array_size = get_random_int() & 0x0F;
>         if (to_user) {
>                 unsigned char array[array_size];
> ....
>                 pr_info("attempting bad copy_to_user of distant stack 2\n");
>                 if (copy_to_user((void __user *)user_addr, array,
>                                  unconst + sizeof(array))) {
>                         pr_warn("copy_to_user failed, but lacked Oops\n");
>                         goto free_user;
>                 }
> ....
> # echo USERCOPY_STACK_FRAME_TO > DIRECT
> [ 1999.832209] Before dynamic alloc: ffffffc079013d40
> [ 1999.832309] After dynamic alloc: ffffffc079013d40
> [ 1999.832370] lkdtm: attempting good copy_to_user of local stack
> [ 1999.832476] lkdtm: attempting bad copy_to_user of distant stack
> [ 1999.832562] usercopy: kernel memory exposure attempt detected from
> ffffffc079013d20 (<process stack>) (32 bytes)
> [ 1999.832636] usercopy: BUG()!!!
> [ 1999.832693] lkdtm: attempting bad copy_to_user of distant stack 2
> [ 1999.832779] usercopy: kernel memory exposure attempt detected from
> ffffffc079013d30 (<process stack>) (6 bytes)
> [ 1999.832853] usercopy: BUG()!!!
>
> This is output of GCC 4.9, so maybe the sp value is not expected one.
> Anyway it looks to me that the object should be scanned from oldframe.

Am I correct in understanding that your code worked correctly? I.e.
Access to "array" worked, but stepping beyond it failed? (Does
sizeof() work with dynamic stack allocations?)

-Kees

-- 
Kees Cook
Pixel Security

Powered by blists - more mailing lists

Your e-mail address:

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.