[PATCH 18/27] bpf: Restrict kernel image access functions when the kernel is locked down
From: Alexei Starovoitov <hidden>
Date: 2017-10-19 22:18:35
Also in:
linux-efi, lkml, netdev
On Thu, Oct 19, 2017 at 03:52:49PM +0100, David Howells wrote:
quoted hunk ↗ jump to hunk
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; + }
That doesn't help the lockdown purpose. If you don't trust the root the only way to prevent bpf read memory is to disable the whole thing. Have a single check in sys_bpf() to disallow everything if kernel_is_locked_down() and don't add overhead to critical path like bpf_probe_read(). -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html