linux-kernel - Re: [RFC][PATCH] Lock down kprobes

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Date:   Thu, 9 Nov 2017 23:00:12 +0530
From:   Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
To:     David Howells <dhowells@...hat.com>
Cc:     alexei.starovoitov@...il.com,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Lock down kprobes

On Thu, Nov 09, 2017 at 04:52:05PM +0000, David Howells wrote:
> Hi,
> 
> I need to lock down kprobes under secure boot conditions as part of the patch
> series that can be found here:
> 
> 	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=efi-lock-down
> 
> Can you tell me that if the attached patch is sufficient to the cause?

Yes, this patch will prevent any kprobe registration.

Ananth

> 
> Thanks,
> David
> ---
> commit ffb3484d6e0f1d625f8e84a6a19c139a28a52499
> Author: David Howells <dhowells@...hat.com>
> Date:   Wed Nov 8 16:14:12 2017 +0000
> 
>     Lock down kprobes
>     
>     Disallow the creation of kprobes when the kernel is locked down by
>     preventing their registration.  This prevents kprobes from being used to
>     access kernel memory, either to make modifications or to steal crypto data.
>     
>     Reported-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
>     Signed-off-by: David Howells <dhowells@...hat.com>
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index a1606a4224e1..f06023b0936c 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1530,6 +1530,9 @@ int register_kprobe(struct kprobe *p)
>  	struct module *probed_mod;
>  	kprobe_opcode_t *addr;
>  
> +	if (kernel_is_locked_down("Use of kprobes"))
> +		return -EPERM;
> +
>  	/* Adjust probe address from symbol */
>  	addr = kprobe_addr(p);
>  	if (IS_ERR(addr))