X.509: Add simple ASN.1 grammar compiler

Add a simple ASN.1 grammar compiler.  This produces a bytecode output that can
be fed to a decoder to inform the decoder how to interpret the ASN.1 stream it
is trying to parse.

Action functions can be specified in the grammar by interpolating:

	({ foo })

after a type, for example:

	SubjectPublicKeyInfo ::= SEQUENCE {
		algorithm		AlgorithmIdentifier,
		subjectPublicKey	BIT STRING ({ do_key_data })
		}

The decoder is expected to call these after matching this type and parsing the
contents if it is a constructed type.

The grammar compiler does not currently support the SET type (though it does
support SET OF) as I can't see a good way of tracking which members have been
encountered yet without using up extra stack space.

Currently, the grammar compiler will fail if more than 256 bytes of bytecode
would be produced or more than 256 actions have been specified as it uses
8-bit jump values and action indices to keep space usage down.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 8 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index af6c7f8ba019..66cc885abbc6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1612,4 +1612,12 @@ config PADATA
         depends on SMP
         bool
 
+config ASN1
+        tristate
+        help
+          Build a simple ASN.1 grammar compiler that produces a bytecode output
+          that can be interpreted by the ASN.1 stream decoder and used to
+          inform it as to what tags are to be expected in a stream and what
+          functions to call on what tags.
+
 source "kernel/Kconfig.locks"