On Thu, Jul 18, 2019 at 12:44:09PM -0700, Matthew Garrett wrote:
> From: David Howells <dhowe...@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.starovoi...@gmail.com>
> Signed-off-by: Matthew Garrett <mj...@google.com>
Reviewed-by: Kees Cook <keesc...@chromium.org>
-Kees
> cc: net...@vger.kernel.org
> cc: Chun-Yi Lee <j...@suse.com>
> cc: Alexei Starovoitov <alexei.starovoi...@gmail.com>
> Cc: Daniel Borkmann <dan...@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
