Hi Alexei,
Thanks for your review!
On Thu, Oct 19, 2017 at 03:18:30PM -0700, Alexei Starovoitov wrote:
On Thu, Oct 19, 2017 at 03:52:49PM +0100, David Howells wrote:
quoted
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.
Not totally untrust root, I don't want that root reads
arbitrary memory address through bpf.
Is it not enough to lock down bpf_probe_read, bpf_probe_write_user
and bpf_trace_printk?
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().
Yes, it give overhead to bpf_probe_read but it prevents arbitrary
memory read.
Another idea is signing bpf bytecode then verifying signture when
loading to kernel.
Thanks a lot!
Joey Lee
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