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

Orabug: 25308134

[ 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>
(cherry picked from commit e9071d07878c865449c5afb062e6d305c62d1e85)
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>

diff --git a/Documentation/module-signing.txt b/Documentation/module-signing.txt
index c72702ec1ded8b0b5d728e6cd0519a5862d2d3c7..aacf1ce73b8a5964d3503a1d99affa799c57c50e 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.