kernel: add section about /proc/version

Customize user, host and date

README.adoc

@@ -5283,6 +5283,26 @@ Sources:
 
 Bibliography: https://stackoverflow.com/questions/8516021/proc-create-example-for-kernel-module/18924359#18924359
 
+===== /proc/version
+
+Its data is shared with `uname()`, which is a POSIX C function and has a Linux syscall to back it up.
+
+Where the data comes from and how to modify it:
+
+* https://unix.stackexchange.com/questions/136959/where-does-uname-get-its-information-from/485962#485962
+* https://stackoverflow.com/questions/23424174/how-to-customize-or-remove-extra-linux-kernel-version-details-shown-at-boot
+
+In this repo, leaking host information, and to make builds more reproducible, we are setting:
+
+- user and date to dummy values
+- hostname to the kernel git commit
+
+So the file contains something like:
+
+....
+Linux version 4.19.0-dirty (lkmc@84df9525b0c27f3ebc2ebb1864fa62a97fdedb7d) (gcc version 6.4.0 (Buildroot 2018.05-00002-gbc60382b8f)) #1 SMP Thu Jan 1 00:00:00 UTC 1970
+....
+
 ==== sysfs
 
 Sysfs is more restricted than <<procfs>>, as it does not take an arbitrary `file_operations`: