[image] Check delimiters when parsing command-line key-value arguments

[image] Check delimiters when parsing command-line key-value arguments

The Linux kernel bzImage image format and the CPIO archive constructor
will parse the image command line for certain arguments of the form
"key=value".  This parsing is currently implemented using strstr() in
a way that can cause a false positive suffix match.  For example, a
command line containing "highmem=<n>" would erroneously be treated as
containing a value for "mem=<n>".

Fix by centralising the logic used for parsing such arguments, and
including a check that the argument immediately follows a whitespace
delimiter (or is at the start of the string).

Reported-by: Filippo Giunchedi <filippo@esaurito.net>
Signed-off-by: Michael Brown <mcb30@ipxe.org>