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Date: Wed, 7 Aug 2019 17:07:15 -0700 From: Matthew Garrett <matthewgarrett@...gle.com> To: jmorris@...ei.org Cc: linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org, David Howells <dhowells@...hat.com>, Alexei Starovoitov <alexei.starovoitov@...il.com>, Matthew Garrett <mjg59@...gle.com>, Kees Cook <keescook@...omium.org>, netdev@...r.kernel.org, Chun-Yi Lee <jlee@...e.com>, Daniel Borkmann <daniel@...earbox.net> Subject: [PATCH V38 23/29] bpf: Restrict bpf when kernel lockdown is in confidentiality mode From: David Howells <dhowells@...hat.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@...il.com> Signed-off-by: Matthew Garrett <mjg59@...gle.com> Reviewed-by: Kees Cook <keescook@...omium.org> cc: netdev@...r.kernel.org cc: Chun-Yi Lee <jlee@...e.com> cc: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Daniel Borkmann <daniel@...earbox.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", }; -- 2.22.0.770.g0f2c4a37fd-goog
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