On Mon, Dec 19, 2022 at 03:40:42PM -0600, Allen Webb wrote: > On Mon, Dec 19, 2022 at 3:23 PM Luis Chamberlain <mcgrof@xxxxxxxxxx> wrote: > > > > On Mon, Dec 19, 2022 at 02:46:18PM -0600, Allen Webb wrote: > > > Update the documentation to include the presense and use case of > > > modules.builtin.alias. > > > > > > Signed-off-by: Allen Webb <allenwebb@xxxxxxxxxx> > > > --- > > > Documentation/kbuild/kbuild.rst | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst > > > index 08f575e6236c..1c7c02040a54 100644 > > > --- a/Documentation/kbuild/kbuild.rst > > > +++ b/Documentation/kbuild/kbuild.rst > > > @@ -17,6 +17,12 @@ modules.builtin > > > This file lists all modules that are built into the kernel. This is used > > > by modprobe to not fail when trying to load something builtin. > > > > > > +modules.builtin.alias > > > +--------------------- > > > +This file lists all match-id based aliases for modules built into the kernel. > > > +These are intended to enable userspace to make authorization decisions based > > > +on which modules are likely to be bound to a device after it is authorized. > > > > What is an example? This sounds obscure. > > Many of the devices that match the usb_storage driver only specify the > vendor id, product id, and device id (VID:PID:D) and do not match > against device class, interface class, etc. Here are some examples > from modules.alias: A grep for wildcards in these fields yields 6136 > matches: > grep 'dc\*dsc\*dp\*ic\*isc\*ip\*in\*' > /lib/modules/5.19.11-1rodete1-amd64/modules.alias | wc -l > 6136 > > To write USBGuard policy that only authorizes devices that bind to a > particular module the policy needs to be aware of all these VID:PID:D > which can change between kernel versions. > > This is done at runtime rather than excluding modules from the build > because some devices are not needed at or before login or when a > device is locked. By not authorizing new devices that would bind to a > set of modules, these modules become unreachable to an attacker who > seeks to exploit kernel bugs in those modules. > > I could add this detail to the documentation file, but I was trying to > keep the description to about the same length as the others around it. How about the second sentence you wrote say something like: An example usage of the built-in aliases is to enable software such as USBGuard to enable / disable specific devices outside of just the vendor, product and device ID. This allows more flexible security policies in userspace. Luis
