bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/bcma/README b/drivers/bcma/README
new file mode 100644
index 000000000..f7e7ce46c
--- /dev/null
+++ b/drivers/bcma/README
@@ -0,0 +1,19 @@
+Broadcom introduced new bus as replacement for older SSB. It is based on AMBA,
+however from programming point of view there is nothing AMBA specific we use.
+
+Standard AMBA drivers are platform specific, have hardcoded addresses and use
+AMBA standard fields like CID and PID.
+
+In case of Broadcom's cards every device consists of:
+1) Broadcom specific AMBA device. It is put on AMBA bus, but can not be treated
+   as standard AMBA device. Reading it's CID or PID can cause machine lockup.
+2) AMBA standard devices called ports or wrappers. They have CIDs (AMBA_CID)
+   and PIDs (0x103BB369), but we do not use that info for anything. One of that
+   devices is used for managing Broadcom specific core.
+
+Addresses of AMBA devices are not hardcoded in driver and have to be read from
+EPROM.
+
+In this situation we decided to introduce separated bus. It can contain up to
+16 devices identified by Broadcom specific fields: manufacturer, id, revision
+and class.