[Xen-devel] [PATCH v3 08/23] x86/xen_hello_world.xsplice: Test payload for patching 'xen_extra_version'. (v2)

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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 (xen_hello_world_func.c).
 - C code generating the .xsplice.funcs structure
   (xen_hello_world.c)
 - The address of the old code (xen_extra_version). We
   retrieve it by  using 'nm --defined' on xen-syms.
 - The size of the new and old code for which we use
   nm --defined -S on our code and xen-syms respectively.

There are two C files and one header files generated
during build. One could make this one C file if the
size of the newly patched function size was known in
advance (or an random value was choosen).

There is also a strict order of compiling:
 1) xen_hello_world_func.c
 2) config.h - extract the size of the new function,
    the old function and the old function address.
 3) xen_hello_world.c - which contains the .xsplice.funcs
    structure.
 4) Link the object files in an xen_hello_world.xsplice file.

The use-case is simple:

$xen-xsplice load /usr/lib/debug/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

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 docs/misc/xsplice.markdown               | 36 +++++++++++++++++++++++
 tools/misc/xsplice.lds                   | 11 +++++++
 xen/Makefile                             |  2 ++
 xen/arch/arm/Makefile                    |  4 +++
 xen/arch/x86/Makefile                    |  6 ++++
 xen/arch/x86/test/Makefile               | 50 ++++++++++++++++++++++++++++++++
 xen/arch/x86/test/xen_hello_world.c      | 15 ++++++++++
 xen/arch/x86/test/xen_hello_world_func.c |  8 +++++
 8 files changed, 132 insertions(+)
 create mode 100644 tools/misc/xsplice.lds
 create mode 100644 xen/arch/x86/test/Makefile
 create mode 100644 xen/arch/x86/test/xen_hello_world.c
 create mode 100644 xen/arch/x86/test/xen_hello_world_func.c

diff --git a/docs/misc/xsplice.markdown b/docs/misc/xsplice.markdown
index 9a95243..0a5b87b 100644
--- a/docs/misc/xsplice.markdown
+++ b/docs/misc/xsplice.markdown
@@ -321,11 +321,47 @@ 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;  
+    uint64_t new_addr;  
+    uint64_t old_addr;  
+    uint32_t new_size;  
+    uint32_t old_size;  
+    uint8_t pad[32];  
+};  
+
+/* Our replacement function for xen_extra_version. */  
+const char *xen_hello_world(void)  
+{  
+    return "Hello World";  
+}  
+
+static unsigned char name[] = "xen_hello_world";  
+
+struct xsplice_patch_func xsplice_hello_world = {  
+    .name = name,  
+    .new_addr = (unsigned long)(xen_hello_world),  
+    .old_addr = 0xffff82d08013963c, /* Extracted from xen-syms. */  
+    .new_size = 13, /* To be be computed by scripts. */  
+    .old_size = 13, /* -----------""---------------  */  
+} __attribute__((__section__(".xsplice.funcs")));  
+
+</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/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) }
+
+}
diff --git a/xen/Makefile b/xen/Makefile
index 5d98bcb..f702525 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -75,6 +75,7 @@ _install: $(TARGET)$(CONFIG_XEN_INSTALL_SUFFIX)
                        echo 'EFI installation only partially done (EFI_VENDOR 
not set)' >&2; \
                fi; \
        fi
+       $(MAKE) -f $(BASEDIR)/Rules.mk -C arch/$(TARGET_ARCH) install
 
 .PHONY: _uninstall
 _uninstall: D=$(DESTDIR)
@@ -92,6 +93,7 @@ _uninstall:
        rm -f $(D)$(EFI_DIR)/$(T)-$(XEN_VERSION).efi
        rm -f $(D)$(EFI_DIR)/$(T).efi
        rm -f 
$(D)$(EFI_MOUNTPOINT)/efi/$(EFI_VENDOR)/$(T)-$(XEN_FULLVERSION).efi
+       $(MAKE) -f $(BASEDIR)/Rules.mk -C arch/$(TARGET_ARCH) uninstall
 
 .PHONY: _debug
 _debug:
diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index f144c14..35ba293 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -56,6 +56,10 @@ ifeq ($(CONFIG_ARM_64),y)
        ln -sf $(notdir $@)  ../../$(notdir $@).efi
 endif
 
+install:
+
+uninstall:
+
 $(TARGET).axf: $(TARGET)-syms
        # XXX: VE model loads by VMA so instead of
        # making a proper ELF we link with LMA == VMA and adjust crudely
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index f7d3e39..51d12ac 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -74,7 +74,12 @@ efi-y := $(shell if [ ! -r $(BASEDIR)/include/xen/compile.h 
-o \
 $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
        ./boot/mkelf32 $(TARGET)-syms $(TARGET) 0x100000 \
        `$(NM) -nr $(TARGET)-syms | head -n 1 | sed -e 's/^\([^ ]*\).*/0x\1/'`
+       $(MAKE) -f $(BASEDIR)/Rules.mk -C test
 
+install:
+       $(MAKE) -f $(BASEDIR)/Rules.mk -C test install
+uninstall:
+       $(MAKE) -f $(BASEDIR)/Rules.mk -C test uninstall
 
 ALL_OBJS := $(BASEDIR)/arch/x86/boot/built_in.o 
$(BASEDIR)/arch/x86/efi/built_in.o $(ALL_OBJS)
 
@@ -178,3 +183,4 @@ clean::
        rm -f $(BASEDIR)/.xen-syms.[0-9]* boot/.*.d
        rm -f $(BASEDIR)/.xen.efi.[0-9]* efi/*.o efi/.*.d efi/*.efi 
efi/disabled efi/mkreloc
        rm -f boot/reloc.S boot/reloc.lnk boot/reloc.bin
+       $(MAKE) -f $(BASEDIR)/Rules.mk -C test clean
diff --git a/xen/arch/x86/test/Makefile b/xen/arch/x86/test/Makefile
new file mode 100644
index 0000000..3fe951d
--- /dev/null
+++ b/xen/arch/x86/test/Makefile
@@ -0,0 +1,50 @@
+include $(XEN_ROOT)/Config.mk
+
+CODE_ADDR=$(shell nm --defined $(1) | grep $(2) | awk '{print "0x"$$1}')
+CODE_SZ=$(shell nm --defined -S $(1) | grep $(2) | awk '{ print "0x"$$2}')
+
+.PHONY: default
+ifdef CONFIG_XSPLICE
+
+XSPLICE := xen_hello_world.xsplice
+
+default: xsplice
+
+install: xsplice
+       $(INSTALL_DATA) $(XSPLICE) $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE)
+uninstall:
+       rm -f $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE)
+else
+default:
+install:
+uninstall:
+endif
+
+.PHONY: clean
+clean::
+       rm -f *.o .*.o.d $(XSPLICE) config.h
+
+#
+# To compute these values we need the binary files: xen-syms
+# and xen_hello_world_func.o to be already compiled.
+#
+# We can be assured that xen-syms is already built as we are
+# the last entry in the build target.
+#
+.PHONY: config.h
+config.h: OLD_CODE=$(call CODE_ADDR,$(BASEDIR)/xen-syms,xen_extra_version)
+config.h: OLD_CODE_SZ=$(call CODE_SZ,$<,xen_hello_world)
+config.h: NEW_CODE_SZ=$(call CODE_SZ,$(BASEDIR)/xen-syms,xen_extra_version)
+config.h: xen_hello_world_func.o
+       (set -e; \
+        echo "#define NEW_CODE_SZ $(NEW_CODE_SZ)"; \
+        echo "#define OLD_CODE_SZ $(OLD_CODE_SZ)"; \
+        echo "#define OLD_CODE $(OLD_CODE)") > $@
+
+.PHONY: xsplice
+xsplice: config.h
+       # Need to have these done in sequential order
+       $(MAKE) -f $(BASEDIR)/Rules.mk xen_hello_world_func.o
+       $(MAKE) -f $(BASEDIR)/Rules.mk xen_hello_world.o
+       $(LD) $(LDFLAGS) -r -o $(XSPLICE) xen_hello_world_func.o 
xen_hello_world.o
+
diff --git a/xen/arch/x86/test/xen_hello_world.c 
b/xen/arch/x86/test/xen_hello_world.c
new file mode 100644
index 0000000..6a1775b
--- /dev/null
+++ b/xen/arch/x86/test/xen_hello_world.c
@@ -0,0 +1,15 @@
+#include <xen/config.h>
+#include <xen/types.h>
+#include <xen/xsplice.h>
+#include "config.h"
+
+static char name[] = "xen_hello_world";
+extern const char *xen_hello_world(void);
+
+struct xsplice_patch_func __section(".xsplice.funcs") xsplice_xen_hello_world 
= {
+    .name = name,
+    .new_addr = (unsigned long)(xen_hello_world),
+    .old_addr = OLD_CODE,
+    .new_size = NEW_CODE_SZ,
+    .old_size = OLD_CODE_SZ,
+};
diff --git a/xen/arch/x86/test/xen_hello_world_func.c 
b/xen/arch/x86/test/xen_hello_world_func.c
new file mode 100644
index 0000000..95ffcbd
--- /dev/null
+++ b/xen/arch/x86/test/xen_hello_world_func.c
@@ -0,0 +1,8 @@
+#include <xen/config.h>
+#include <xen/types.h>
+
+/* Our replacement function for xen_extra_version. */
+const char *xen_hello_world(void)
+{
+    return "Hello World";
+}
-- 
2.1.0


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