[PATCH 18/27] bpf: Restrict kernel image access functions when the kernel is locked down
STALE3222d
From: dhowells@redhat.com (David Howells)
Date: 2017-10-19 14:52:55
Also in:
linux-efi, lkml
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [security & lsm] (security audit and enforcement using bpf), bpf [tracing], the rest, tracing · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, KP Singh, Matt Bobrowski, Song Liu, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
From: Chun-Yi Lee <jlee@suse.com> There are some bpf functions can be used to read kernel memory: bpf_probe_read, bpf_probe_write_user and bpf_trace_printk. These allow private keys in kernel memory (e.g. the hibernation image signing key) to be read by an eBPF program. Prohibit those functions when the kernel is locked down. Signed-off-by: Chun-Yi Lee <jlee@suse.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: netdev at vger.kernel.org --- kernel/trace/bpf_trace.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index dc498b605d5d..35e85a3fdb37 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c@@ -65,6 +65,11 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr) { int ret; + if (kernel_is_locked_down("BPF")) { + memset(dst, 0, size); + return -EPERM; + } + ret = probe_kernel_read(dst, unsafe_ptr, size); if (unlikely(ret < 0)) memset(dst, 0, size);
@@ -84,6 +89,9 @@ static const struct bpf_func_proto bpf_probe_read_proto = { BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src, u32, size) { + if (kernel_is_locked_down("BPF")) + return -EPERM; + /* * Ensure we're in user context which is safe for the helper to * run. This helper has no business in a kthread.
@@ -143,6 +151,9 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1, if (fmt[--fmt_size] != 0) return -EINVAL; + if (kernel_is_locked_down("BPF")) + return __trace_printk(1, fmt, 0, 0, 0); + /* check format string for allowed specifiers */ for (i = 0; i < fmt_size; i++) { if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i])) --
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