From: Kees Cook <keescook@chromium.org>
To: Matthew Garrett <matthewgarrett@google.com>
Cc: jmorris@namei.org, linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
David Howells <dhowells@redhat.com>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Matthew Garrett <mjg59@google.com>,
netdev@vger.kernel.org, Chun-Yi Lee <jlee@suse.com>,
Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH V36 23/29] bpf: Restrict bpf when kernel lockdown is in confidentiality mode
Date: Thu, 18 Jul 2019 14:06:39 -0700 [thread overview]
Message-ID: <201907181406.001618FB6@keescook> (raw)
In-Reply-To: <20190718194415.108476-24-matthewgarrett@google.com>
On Thu, Jul 18, 2019 at 12:44:09PM -0700, Matthew Garrett wrote:
> From: David Howells <dhowells@redhat.com>
>
> bpf_read() and bpf_read_str() could potentially be abused to (eg) allow
> private keys in kernel memory to be leaked. Disable them if the kernel
> has been locked down in confidentiality mode.
>
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
> cc: netdev@vger.kernel.org
> cc: Chun-Yi Lee <jlee@suse.com>
> cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> ---
> include/linux/security.h | 1 +
> kernel/trace/bpf_trace.c | 10 ++++++++++
> security/lockdown/lockdown.c | 1 +
> 3 files changed, 12 insertions(+)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 987d8427f091..8dd1741a52cd 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -118,6 +118,7 @@ enum lockdown_reason {
> LOCKDOWN_INTEGRITY_MAX,
> LOCKDOWN_KCORE,
> LOCKDOWN_KPROBES,
> + LOCKDOWN_BPF_READ,
> LOCKDOWN_CONFIDENTIALITY_MAX,
> };
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index ca1255d14576..492a8bfaae98 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -142,8 +142,13 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
> {
> int ret;
>
> + ret = security_locked_down(LOCKDOWN_BPF_READ);
> + if (ret < 0)
> + goto out;
> +
> ret = probe_kernel_read(dst, unsafe_ptr, size);
> if (unlikely(ret < 0))
> +out:
> memset(dst, 0, size);
>
> return ret;
> @@ -569,6 +574,10 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
> {
> int ret;
>
> + ret = security_locked_down(LOCKDOWN_BPF_READ);
> + if (ret < 0)
> + goto out;
> +
> /*
> * The strncpy_from_unsafe() call will likely not fill the entire
> * buffer, but that's okay in this circumstance as we're probing
> @@ -580,6 +589,7 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
> */
> ret = strncpy_from_unsafe(dst, unsafe_ptr, size);
> if (unlikely(ret < 0))
> +out:
> memset(dst, 0, size);
>
> return ret;
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index 6b123cbf3748..1b89d3e8e54d 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -33,6 +33,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_INTEGRITY_MAX] = "integrity",
> [LOCKDOWN_KCORE] = "/proc/kcore access",
> [LOCKDOWN_KPROBES] = "use of kprobes",
> + [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
> [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
> };
>
> --
> 2.22.0.510.g264f2c817a-goog
>
--
Kees Cook
next prev parent reply other threads:[~2019-07-18 21:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190718194415.108476-1-matthewgarrett@google.com>
2019-07-18 19:44 ` [PATCH V36 23/29] bpf: Restrict bpf when kernel lockdown is in confidentiality mode Matthew Garrett
2019-07-18 21:06 ` Kees Cook [this message]
2019-07-29 21:47 ` Matthew Garrett
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