Re: [PATCH v2 02/11] mm: Hardened usercopy
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- To: bsingharora@xxxxxxxxx
- Subject: Re: [PATCH v2 02/11] mm: Hardened usercopy
- From: Kees Cook <keescook@xxxxxxxxxxxx>
- Date: Thu, 14 Jul 2016 21:25:42 -0700
- Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Casey Schaufler <casey@xxxxxxxxxxxxxxxx>, PaX Team <pageexec@xxxxxxxxxxx>, Brad Spengler <spender@xxxxxxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will.deacon@xxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, "x86@xxxxxxxxxx" <x86@xxxxxxxxxx>, Christoph Lameter <cl@xxxxxxxxx>, Pekka Enberg <penberg@xxxxxxxxxx>, David Rientjes <rientjes@xxxxxxxxxx>, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Mathias Krause <minipli@xxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Vitaly Wool <vitalywool@xxxxxxxxx>, Andrea Arcangeli <aarcange@xxxxxxxxxx>, Dmitry Vyukov <dvyukov@xxxxxxxxxx>, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, linux-ia64@xxxxxxxxxxxxxxx, "linuxppc-dev@xxxxxxxxxxxxxxxx" <linuxppc-dev@xxxxxxxxxxxxxxxx>, sparclinux <sparclinux@xxxxxxxxxxxxxxx>, linux-arch <linux-arch@xxxxxxxxxxxxxxx>, Linux-MM <linux-mm@xxxxxxxxx>, "kernel-hardening@xxxxxxxxxxxxxxxxxx" <kernel-hardening@xxxxxxxxxxxxxxxxxx>
- In-reply-to: <20160714232019.GA28254@350D>
- List-id: <linux-ia64.vger.kernel.org>
- References: <1468446964-22213-1-git-send-email-keescook@chromium.org> <1468446964-22213-3-git-send-email-keescook@chromium.org> <20160714232019.GA28254@350D>
On Thu, Jul 14, 2016 at 4:20 PM, Balbir Singh <bsingharora@xxxxxxxxx> wrote:
> On Wed, Jul 13, 2016 at 02:55:55PM -0700, Kees Cook wrote:
>> [...]
>> +++ b/mm/usercopy.c
>> @@ -0,0 +1,219 @@
>> [...]
>> +/*
>> + * Checks if a given pointer and length is contained by the current
>> + * stack frame (if possible).
>> + *
>> + * 0: not at all on the stack
>> + * 1: fully within a valid stack frame
>> + * 2: fully on the stack (when can't do frame-checking)
>> + * -1: error condition (invalid stack position or bad stack frame)
>
> Can we use enums? Makes it easier to read/debug
Sure, I will update this.
>> [...]
>> +static void report_usercopy(const void *ptr, unsigned long len,
>> + bool to_user, const char *type)
>> +{
>> + pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n",
>> + to_user ? "exposure" : "overwrite",
>> + to_user ? "from" : "to", ptr, type ? : "unknown", len);
>> + dump_stack();
>> + do_group_exit(SIGKILL);
>
> SIGKILL -- SIGBUS?
I'd like to keep SIGKILL since it indicates a process fiddling with a
kernel bug. The real problem here is that there doesn't seem to be an
arch-independent way to Oops the kernel and kill a process ("die()" is
closest, but it's defined on a per-arch basis with varying arguments).
This could be a BUG, but I'd rather not panic the entire kernel.
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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