Documentation/module-signing.txt: Note need for version info if reusing a key

[ Upstream commit b8612e517c3c9809e1200b72c474dbfd969e5a83 ]

Signing a module should only make it trusted by the specific kernel it
was built for, not anything else.  If a module signing key is used for
multiple ABI-incompatible kernels, the modules need to include enough
version information to distinguish them.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/Documentation/module-signing.txt b/Documentation/module-signing.txt
index 09c2382ad0556b196a3b4bb941b9e86597e8ebc5..e3af8c27eef253bd836d00197cf52dde91351fd3 100644 (file)
--- a/Documentation/module-signing.txt
+++ b/Documentation/module-signing.txt
@@ -239,3 +239,9 @@ Since the private key is used to sign modules, viruses and malware could use
 the private key to sign modules and compromise the operating system.  The
 private key must be either destroyed or moved to a secure location and not kept
 in the root node of the kernel source tree.
+
+If you use the same private key to sign modules for multiple kernel
+configurations, you must ensure that the module version information is
+sufficient to prevent loading a module into a different kernel.  Either
+set CONFIG_MODVERSIONS=y or ensure that each configuration has a different
+kernel release string by changing EXTRAVERSION or CONFIG_LOCALVERSION.