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, 55 insertions, 0 deletions

diff --git a/Documentation/i2c/old-module-parameters.rst b/Documentation/i2c/old-module-parameters.rst
new file mode 100644
index 000000000..b08b6daab
--- /dev/null
+++ b/Documentation/i2c/old-module-parameters.rst
@@ -0,0 +1,55 @@
+================================================================
+I2C device driver binding control from user-space in old kernels
+================================================================
+
+.. NOTE::
+   Note: this section is only relevant if you are handling some old code
+   found in kernel 2.6. If you work with more recent kernels, you can
+   safely skip this section.
+
+Up to kernel 2.6.32, many I2C drivers used helper macros provided by
+<linux/i2c.h> which created standard module parameters to let the user
+control how the driver would probe I2C buses and attach to devices. These
+parameters were known as ``probe`` (to let the driver probe for an extra
+address), ``force`` (to forcibly attach the driver to a given device) and
+``ignore`` (to prevent a driver from probing a given address).
+
+With the conversion of the I2C subsystem to the standard device driver
+binding model, it became clear that these per-module parameters were no
+longer needed, and that a centralized implementation was possible. The new,
+sysfs-based interface is described in
+Documentation/i2c/instantiating-devices.rst, section
+"Method 4: Instantiate from user-space".
+
+Below is a mapping from the old module parameters to the new interface.
+
+Attaching a driver to an I2C device
+-----------------------------------
+
+Old method (module parameters)::
+
+  # modprobe <driver> probe=1,0x2d
+  # modprobe <driver> force=1,0x2d
+  # modprobe <driver> force_<device>=1,0x2d
+
+New method (sysfs interface)::
+
+  # echo <device> 0x2d > /sys/bus/i2c/devices/i2c-1/new_device
+
+Preventing a driver from attaching to an I2C device
+---------------------------------------------------
+
+Old method (module parameters)::
+
+  # modprobe <driver> ignore=1,0x2f
+
+New method (sysfs interface)::
+
+  # echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device
+  # modprobe <driver>
+
+Of course, it is important to instantiate the ``dummy`` device before loading
+the driver. The dummy device will be handled by i2c-core itself, preventing
+other drivers from binding to it later on. If there is a real device at the
+problematic address, and you want another driver to bind to it, then simply
+pass the name of the device in question instead of ``dummy``.