libxc: add LZ4 decompression support

Since there's no shared or static library to link against, this simply
re-uses the hypervisor side code. However, I only audited the code
added here for possible security issues, not the referenced code in
the hypervisor tree.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I intentionally retained the tab indentation in the code cloned from
its hypervisor original (which in turn retained it as being a clone
of the Linux original), to ease diff-ing.

--- a/tools/libxc/xc_dom_bzimageloader.c
+++ b/tools/libxc/xc_dom_bzimageloader.c
@@ -573,6 +573,124 @@ int xc_try_xz_decode(struct xc_dom_image
 
 #endif /* !__MINIOS__ */
 
+#define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+#define STATIC static
+#define u8 uint8_t
+#define u16 uint16_t
+#define u32 uint32_t
+#define u64 uint64_t
+#define INIT
+#define unlikely(x) (x)
+
+static inline uint_fast16_t le16_to_cpup(const unsigned char *buf)
+{
+    return buf[0] | (buf[1] << 8);
+}
+
+static inline uint_fast32_t le32_to_cpup(const unsigned char *buf)
+{
+    return le16_to_cpup(buf) | ((uint32_t)le16_to_cpup(buf + 2) << 16);
+}
+
+#include "../../xen/common/lz4/decompress.c"
+
+/*
+ * Note: Uncompressed chunk size is used in the compressor side
+ * (userspace side for compression).
+ * It is hardcoded because there is not proper way to extract it
+ * from the binary stream which is generated by the preliminary
+ * version of LZ4 tool so far.
+ */
+#define LZ4_DEFAULT_UNCOMPRESSED_CHUNK_SIZE (8 << 20)
+#define ARCHIVE_MAGICNUMBER 0x184C2102
+
+static int xc_try_lz4_decode(
+	struct xc_dom_image *dom, void **blob, size_t *psize)
+{
+	int ret = -1;
+	size_t uncomp_chunksize = LZ4_DEFAULT_UNCOMPRESSED_CHUNK_SIZE;
+	unsigned char *inp = *blob, *output, *outp;
+	ssize_t size = *psize - 4;
+	size_t out_size, out_len, dest_len, chunksize;
+	const char *msg;
+
+	if (size < 4) {
+		msg = "input too small";
+		goto exit_0;
+	}
+
+	out_size = out_len = get_unaligned_le32(inp + size);
+	if (xc_dom_kernel_check_size(dom, out_len)) {
+		msg = "Decompressed image too large";
+		goto exit_0;
+	}
+
+	output = malloc(out_len);
+	if (!output) {
+		msg = "Could not allocate output buffer";
+		goto exit_0;
+	}
+	outp = output;
+
+	chunksize = get_unaligned_le32(inp);
+	if (chunksize == ARCHIVE_MAGICNUMBER) {
+		inp += 4;
+		size -= 4;
+	} else {
+		msg = "invalid header";
+		goto exit_2;
+	}
+
+	for (;;) {
+		if (size < 4) {
+			msg = "missing data";
+			goto exit_2;
+		}
+		chunksize = get_unaligned_le32(inp);
+		if (chunksize == ARCHIVE_MAGICNUMBER) {
+			inp += 4;
+			size -= 4;
+			continue;
+		}
+		inp += 4;
+		size -= 4;
+
+		if (out_len >= uncomp_chunksize) {
+			dest_len = uncomp_chunksize;
+			out_len -= dest_len;
+		} else
+			dest_len = out_len;
+		ret = lz4_decompress(inp, &chunksize, outp, dest_len);
+		if (ret < 0) {
+			msg = "decoding failed";
+			goto exit_2;
+		}
+
+		outp += dest_len;
+		size -= chunksize;
+
+		if (size == 0)
+		{
+			*blob = output;
+			*psize = out_size;
+			return 0;
+		}
+
+		if (size < 0) {
+			msg = "data corrupted";
+			goto exit_2;
+		}
+
+		inp += chunksize;
+	}
+
+exit_2:
+	free(output);
+	DOMPRINTF("LZ4 decompression error: %s\n", msg);
+exit_0:
+	return ret;
+}
+
 struct setup_header {
     uint8_t  _pad0[0x1f1];  /* skip uninteresting stuff */
     uint8_t  setup_sects;
@@ -733,6 +851,17 @@ static int xc_dom_probe_bzimage_kernel(s
             return -EINVAL;
         }
     }
+    else if ( check_magic(dom, "\x02\x21", 2) )
+    {
+        ret = xc_try_lz4_decode(dom, &dom->kernel_blob, &dom->kernel_size);
+        if ( ret < 0 )
+        {
+            xc_dom_panic(dom->xch, XC_INVALID_KERNEL,
+                         "%s unable to LZ4 decompress kernel\n",
+                         __FUNCTION__);
+            return -EINVAL;
+        }
+    }
     else
     {
         xc_dom_panic(dom->xch, XC_INVALID_KERNEL,
--- a/xen/common/lz4/decompress.c
+++ b/xen/common/lz4/decompress.c
@@ -151,7 +151,7 @@ _output_error:
 	return (int) (-(((unsigned char *)ip) - source));
 }
 
-#ifndef __XEN__
+#if !defined(__XEN__) && !defined(__XEN_TOOLS__)
 static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,
 				int isize, size_t maxoutputsize)
 {
@@ -294,7 +294,7 @@ exit_0:
 	return ret;
 }
 
-#ifndef __XEN__
+#if !defined(__XEN__) && !defined(__XEN_TOOLS__)
 int lz4_decompress_unknownoutputsize(const char *src, size_t src_len,
 		char *dest, size_t *dest_len)
 {