This change demonstrates how to generate an xSplice ELF payload.
The idea here is that we want to patch in the hypervisor
the 'xen_version_extra' function with an function that will
return 'Hello World'. The 'xl info | grep extraversion'
will reflect the new value after the patching.
To generate this ELF payload file we need:
- C code of the new code.
- C code generating the .xsplice.func structure.
- The address of the old code (xen_extra_version). We
do it by using 'nm' but that is a bit of hack.
The linker script file:
- Discards .debug* and .comments* sections.
- Changes the name of .data.local.xsplice_hello_world to
.xsplice.func
- Figures out the size of the new code.
Also if you are curious on the input/output sections
magic the linker does, add these to the GCC line:
-Wl,-M -Wl,-t -Wl,-verbose
which are: print linking map, provide trace and be verbose.
The use-case is simple:
$xen-xsplice load /usr/lib/xen/bin/xen_hello_world.xsplice
$xen-xsplice list
ID | status
----------------------------------------+------------
xen_hello_world APPLIED
$xl info | grep extra
xen_extra : Hello World
$xen-xsplice revert xen_hello_world
Performing revert: completed
$xen-xsplice unload xen_hello_world
Performing unload: completed
$xl info | grep extra
xen_extra : -unstable
Note that it does not build under a 32-bit toolstack as
there is no access to the hypervisor (xen-syms).
We also force it to be built every time - as the hypervisor
may have been rebuilt.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
---
docs/misc/xsplice.markdown | 50 ++++++++++++++++++++++++++++++++++++++++++++
tools/misc/Makefile | 25 +++++++++++++++++++++-
tools/misc/xen_hello_world.c | 15 +++++++++++++
tools/misc/xsplice.h | 12 +++++++++++
tools/misc/xsplice.lds | 11 ++++++++++
5 files changed, 112 insertions(+), 1 deletion(-)
create mode 100644 tools/misc/xen_hello_world.c
create mode 100644 tools/misc/xsplice.h
create mode 100644 tools/misc/xsplice.lds
diff --git a/docs/misc/xsplice.markdown b/docs/misc/xsplice.markdown
index beb452e..e2cdcff 100644
--- a/docs/misc/xsplice.markdown
+++ b/docs/misc/xsplice.markdown
@@ -312,11 +312,61 @@ size.
When applying the patch the hypervisor iterates over each `xsplice_patch_func`
structure and the core code inserts a trampoline at `old_addr` to `new_addr`.
+The `new_addr` is altered when the ELF payload is loaded.
When reverting a patch, the hypervisor iterates over each `xsplice_patch_func`
and the core code copies the data from the undo buffer (private internal copy)
to `old_addr`.
+### Example
+
+A simple example of what a payload file can be:
+
+<pre>
+/* MUST be in sync with hypervisor. */
+struct xsplice_patch_func {
+ const char *name;
+ unsigned long new_addr;
+ const unsigned long old_addr;
+ uint32_t new_size;
+ const uint32_t old_size;
+ uint8_t pad[32];
+};
+
+/* Our replacement function for xen_extra_version. */
+const char *xen_hello_world(void)
+{
+ return "Hello World";
+}
+
+struct xsplice_patch_func xsplice_hello_world = {
+ .name = "xen_extra_version",
+ .new_addr = &xen_hello_world,
+ .old_addr = 0xffff82d08013963c, /* Extracted from xen-syms. */
+ .new_size = 13, /* To be be computed by scripts. */
+ .old_size = 13, /* -----------""--------------- */
+};
+</pre>
+
+With the linker script as follow to change the `xsplice_hello_world`
+do be `.xsplice.funcs` :
+
+<pre>
+OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64")
+OUTPUT_ARCH(i386:x86-64)
+ENTRY(xsplice_hello_world)
+SECTIONS
+{
+ /* The hypervisor expects ".xsplice.func", so change
+ * the ".data.xsplice_hello_world" to it. */
+
+ .xsplice.funcs : { *(*.xsplice_hello_world) }
+ }
+}
+</pre>
+
+Code must be compiled with -fPIC.
+
## Hypercalls
We will employ the sub operations of the system management hypercall (sysctl).
diff --git a/tools/misc/Makefile b/tools/misc/Makefile
index c46873e..8385830 100644
--- a/tools/misc/Makefile
+++ b/tools/misc/Makefile
@@ -36,6 +36,10 @@ INSTALL_SBIN += $(INSTALL_SBIN-y)
# Everything to be installed in a private bin/
INSTALL_PRIVBIN += xenpvnetboot
+# We need the hypervisor - and only 64-bit builds have it.
+ifeq ($(XEN_COMPILE_ARCH),x86_64)
+INSTALL_PRIVBIN += xen_hello_world.xsplice
+endif
# Everything to be installed
TARGETS_ALL := $(INSTALL_BIN) $(INSTALL_SBIN) $(INSTALL_PRIVBIN)
@@ -49,7 +53,7 @@ TARGETS_COPY += xenpvnetboot
# Everything which needs to be built
TARGETS_BUILD := $(filter-out $(TARGETS_COPY),$(TARGETS_ALL))
-.PHONY: all build
+.PHONY: all build xsplice
all build: $(TARGETS_BUILD)
.PHONY: install
@@ -111,4 +115,23 @@ gtraceview: gtraceview.o
xencov: xencov.o
$(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
+.PHONY: xsplice
+xsplice:
+ifeq ($(XEN_COMPILE_ARCH),x86_64)
+ # We MUST regenerate the file everytime we build - in case the
hypervisor
+ # is rebuilt too.
+ $(RM) *.xplice
+ $(MAKE) xen_hello_world.xsplice
+endif
+
+XEN_EXTRA_VERSION_ADDR=$(shell nm --defined $(XEN_ROOT)/xen/xen-syms | grep
xen_extra_version | awk '{print "0x"$$1}')
+
+xen_hello_world.xsplice: xen_hello_world.c
+ $(CC) -DOLD_CODE=$(XEN_EXTRA_VERSION_ADDR) -I$(XEN_ROOT)/tools/include \
+ -fPIC -Wl,--emit-relocs \
+ -Wl,-r -Wl,--entry=xsplice_hello_world \
+ -fdata-sections -ffunction-sections \
+ -nostdlib -Txsplice.lds \
+ -o $@ $<
+ @objdump -x --section=.xsplice.funcs $@
-include $(DEPS)
diff --git a/tools/misc/xen_hello_world.c b/tools/misc/xen_hello_world.c
new file mode 100644
index 0000000..8c24d8f
--- /dev/null
+++ b/tools/misc/xen_hello_world.c
@@ -0,0 +1,15 @@
+#include "xsplice.h"
+
+/* Our replacement function for xen_extra_version. */
+const char *xen_hello_world(void)
+{
+ return "Hello World";
+}
+
+struct xsplice_patch_func xsplice_hello_world = {
+ .name = "xen_extra_version",
+ .new_addr = &xen_hello_world,
+ .old_addr = OLD_CODE,
+ .new_size = 13, /* TODO: Compute. */
+ .old_size = 13, /* TODO: Compute. */
+};
diff --git a/tools/misc/xsplice.h b/tools/misc/xsplice.h
new file mode 100644
index 0000000..6ce8bae
--- /dev/null
+++ b/tools/misc/xsplice.h
@@ -0,0 +1,12 @@
+#include <stdint.h>
+#include <sys/types.h>
+
+/* MUST be in sync with hypervisor. */
+struct xsplice_patch_func {
+ const char *name;
+ unsigned long new_addr;
+ const unsigned long old_addr;
+ uint32_t new_size;
+ const uint32_t old_size;
+ uint8_t pad[32];
+};
diff --git a/tools/misc/xsplice.lds b/tools/misc/xsplice.lds
new file mode 100644
index 0000000..f52eb8c
--- /dev/null
+++ b/tools/misc/xsplice.lds
@@ -0,0 +1,11 @@
+OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64")
+OUTPUT_ARCH(i386:x86-64)
+ENTRY(xsplice_hello_world)
+SECTIONS
+{
+ /* The hypervisor expects ".xsplice.func", so change
+ * the ".data.xsplice_hello_world" to it. */
+
+ .xsplice.funcs : { *(*.xsplice_hello_world) }
+
+}
--
2.1.0
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