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>
---
v3: Fix placement of DOMPRINTF() invocation. Split implementation into
    its own source file. Use the safe decompressor variant in non-
    Mini-OS libxc (lz4_decompress_unknownoutputsize()).
---
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/Makefile
+++ b/tools/libxc/Makefile
@@ -63,6 +63,7 @@ $(patsubst %.c,%.opic,$(ELF_SRCS-y)): CF
 GUEST_SRCS-y                 += xc_dom_core.c xc_dom_boot.c
 GUEST_SRCS-y                 += xc_dom_elfloader.c
 GUEST_SRCS-$(CONFIG_X86)     += xc_dom_bzimageloader.c
+GUEST_SRCS-$(CONFIG_X86)     += xc_dom_decompress_lz4.c
 GUEST_SRCS-$(CONFIG_ARM)     += xc_dom_armzimageloader.c
 GUEST_SRCS-y                 += xc_dom_binloader.c
 GUEST_SRCS-y                 += xc_dom_compat_linux.c
--- a/tools/libxc/xc_dom_bzimageloader.c
+++ b/tools/libxc/xc_dom_bzimageloader.c
@@ -33,7 +33,7 @@
 #include <inttypes.h>
 
 #include "xg_private.h"
-#include "xc_dom.h"
+#include "xc_dom_decompress.h"
 
 #ifndef __MINIOS__
 
@@ -733,6 +733,17 @@ 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,
--- /dev/null
+++ b/tools/libxc/xc_dom_decompress.h
@@ -0,0 +1,8 @@
+#ifndef __MINIOS__
+# include "xc_dom.h"
+#else
+# include "xc_dom_decompress_unsafe.h"
+#endif
+
+int xc_try_lz4_decode(struct xc_dom_image *dom, void **blob, size_t *size);
+
--- /dev/null
+++ b/tools/libxc/xc_dom_decompress_lz4.c
@@ -0,0 +1,132 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <endian.h>
+#include <stdint.h>
+
+#include "xg_private.h"
+#include "xc_dom_decompress.h"
+
+#define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+
+typedef uint8_t u8;
+typedef uint16_t u16;
+typedef uint32_t u32;
+typedef uint64_t u64;
+
+#define likely(a) a
+#define unlikely(a) a
+
+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/include/xen/lz4.h"
+#include "../../xen/common/decompress.h"
+
+#ifndef __MINIOS__
+
+#include "../../xen/common/lz4/decompress.c"
+
+#define ARCHIVE_MAGICNUMBER 0x184C2102
+
+int xc_try_lz4_decode(
+	struct xc_dom_image *dom, void **blob, size_t *psize)
+{
+	int ret = -1;
+	unsigned char *inp = *blob, *output, *outp;
+	ssize_t size = *psize - 4;
+	size_t out_len, dest_len, chunksize;
+	const char *msg;
+
+	if (size < 4) {
+		msg = "input too small";
+		goto exit_0;
+	}
+
+	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;
+
+		dest_len = out_len - (outp - output);
+		ret = lz4_decompress_unknownoutputsize(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_len;
+			return 0;
+		}
+
+		if (size < 0) {
+			msg = "data corrupted";
+			goto exit_2;
+		}
+
+		inp += chunksize;
+	}
+
+exit_2:
+	free(output);
+exit_0:
+	DOMPRINTF("LZ4 decompression error: %s\n", msg);
+	return ret;
+}
+
+#else /* __MINIOS__ */
+
+#include "../../xen/common/unlz4.c"
+
+int xc_try_lz4_decode(
+    struct xc_dom_image *dom, void **blob, size_t *size)
+{
+    return xc_dom_decompress_unsafe(unlz4, dom, blob, size);
+}
+
+#endif