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Date:   Tue, 26 Mar 2019 21:29:57 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Matthew Garrett <matthewgarrett@google.com>
Cc:     jmorris@namei.org, linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, dhowells@redhat.com,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        "Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        davem@davemloft.net, Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH 22/27] Lock down kprobes
Message-Id: <20190326212957.f5b518990c14cf21262bfdcc@kernel.org>
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        <20190325220954.29054-23-matthewgarrett@google.com>
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On Mon, 25 Mar 2019 15:09:49 -0700
Matthew Garrett <matthewgarrett@google.com> wrote:

> From: David Howells <dhowells@redhat.com>
> 
> 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.

Hmm, if you enforce signature check of modules, those modules
should be allowed to use kprobes?
I think we should introduce some kind of trust inheritance from
signed (trusted) modules.

Thank you,

> 
> Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Signed-off-by: Matthew Garrett <matthewgarrett@google.com>
> Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
> Cc: davem@davemloft.net
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  kernel/kprobes.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index f4ddfdd2d07e..6f66cca8e2c6 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1552,6 +1552,9 @@ 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))
> -- 
> 2.21.0.392.gf8f6787159e-goog
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>