prog, pkg/compiler: add `BufferCompressed` buffer type & `compressed_image` builtin

Create the `BufferCompressed` kind of `BufferType`, which will be used
to represent compressed data. Create the corresponding `compressed_image`
syzlang builtin, which is backed by `BufferCompressed`. For now, no
syscalls use this feature - this will be introduced in future commits.

We have to be careful to decompress the data before mutating, and
re-compress before storing. We make sure that any deserialised
`BufferCompressed` data is valid too.

`BufferCompressed` arguments are mutated using a generic heatmap. In
future, we could add variants of `BufferCompressed` or populate the
`BufferType` sub-kind, using it to choose different kinds of heatmap for
different uncompressed data formats.

Various operations on compressed data must be forbidden, so we check for
`BufferCompressed` in key places. We also have to ensure `compressed_image`
can only be used in syscalls that are marked `no_{generate,minimize}`.
Therefore, we add a generic compiler check which allows type
descriptions to require attributes on the syscalls which use them.

1 files changed, 9 insertions, 0 deletions

diff --git a/prog/encoding.go b/prog/encoding.go
index 92b7f2be3..82c93273a 100644
--- a/prog/encoding.go
+++ b/prog/encoding.go
@@ -597,6 +597,15 @@ func (p *parser) parseArgString(t Type, dir Dir) (Arg, error) {
 	if err != nil {
 		return nil, err
 	}
+	// Check compressed data for validity.
+	if typ.IsCompressed() {
+		_, err = Decompress(data)
+		if err != nil {
+			p.strictFailf("invalid compressed data in arg: %v", err)
+			// In non-strict mode, empty the data slice.
+			data = Compress([]byte{})
+		}
+	}
 	size := ^uint64(0)
 	if p.Char() == '/' {
 		p.Parse('/')