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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v4 29/34] xsplice: Stacking build-id dependency checking.
We now expect that the ELF payloads be built with the
--build-id.
Also the .xsplice.deps section has to have the contents
of the hypervisor (or a preceding payload) build-id.
We already have the code to verify the Elf_Note build-id
so export parts of it.
This dependency means the hypervisor MUST be compiled with
--build-id - so we gate the build of xSplice on the availability
of said functionality.
This does not impact the ordering of how the payloads can
be loaded, but it does enforce an STRICT ordering when the
payloads are applied. Also the REPLACE is special - we need
to check that its dependency against the hypervisor - not
the last applied patch.
To make this easier to test we also add an extra test-case
to be used - which can only be applied on top of the
xen_hello_world payload.
As in, one can apply xen_hello_world and then xen_bye_world
on top of that. Not the other way.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
v2: Andrew fix against the build_id.o mutilations.
v3: Andrew fix to not include extra symbols in binary.id
---
Config.mk | 1 +
docs/misc/xsplice.markdown | 84 ++++++++++++++++++---------
xen/arch/x86/test/Makefile | 41 +++++++++++--
xen/arch/x86/test/xen_bye_world.c | 35 +++++++++++
xen/arch/x86/test/xen_bye_world_func.c | 25 ++++++++
xen/common/Kconfig | 5 ++
xen/common/version.c | 40 +++++++++----
xen/common/xsplice.c | 102 ++++++++++++++++++++++++++++++++-
xen/include/xen/version.h | 3 +
xen/include/xen/xsplice.h | 5 ++
10 files changed, 297 insertions(+), 44 deletions(-)
create mode 100644 xen/arch/x86/test/xen_bye_world.c
create mode 100644 xen/arch/x86/test/xen_bye_world_func.c
diff --git a/Config.mk b/Config.mk
index c8e89fe..80629e3 100644
--- a/Config.mk
+++ b/Config.mk
@@ -134,6 +134,7 @@ ifeq ($(call ld-ver-build-id,$(LD)),n)
build_id_linker :=
else
CFLAGS += -DBUILD_ID
+export XEN_HAS_BUILD_ID=y
build_id_linker := --build-id=sha1
endif
diff --git a/docs/misc/xsplice.markdown b/docs/misc/xsplice.markdown
index d1f2a5b..c453b67 100644
--- a/docs/misc/xsplice.markdown
+++ b/docs/misc/xsplice.markdown
@@ -283,8 +283,7 @@ The xSplice core code loads the payload as a standard ELF
binary, relocates it
and handles the architecture-specifc sections as needed. This process is much
like what the Linux kernel module loader does.
-The payload contains a section (xsplice_patch_func) with an array of structures
-describing the functions to be patched:
+The payload contains at least three sections:
It optionally may contain the address of functions to be called right before
being applied and after being reverted:
@@ -292,6 +291,15 @@ being applied and after being reverted:
* `.xsplice.hooks.unload` - an array of function pointers.
+ * `.xsplice.funcs` - which is an array of xsplice_patch_func structures.
+ * `.xsplice.depends` - which is an ELF Note that describes what the payload
+ depends on.
+ * `.note.gnu.build-id` - the build-id of this payload.
+
+### .xsplice.funcs
+
+The `.xsplice.funcs` contains an array of xsplice_patch_func structures
+which describe the functions to be patched:
<pre>
struct xsplice_patch_func {
const char *name;
@@ -333,7 +341,7 @@ 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
+### Example of .xsplice.funcs
A simple example of what a payload file can be:
@@ -379,10 +387,29 @@ Each entry in this array is eight bytes.
The type definition of the function are as follow:
+
<pre>
typedef void (*xsplice_loadcall_t)(void);
typedef void (*xsplice_unloadcall_t)(void);
</pre>
+
+### .xsplice.depends and .note.gnu.build-id
+
+To support dependencies checking and safe loading (to load the
+appropiate payload against the right hypervisor) there is a need
+to embbed an build-id dependency.
+
+This is done by the payload containing an section `.xsplice.depends`
+which follows the format of an ELF Note. The contents of this
+(name, and description) are specific to the linker utilized to
+build the hypevisor and payload.
+
+If GNU linker is used then the name is `GNU` and the description
+is an NT_GNU_BUILD_ID type ID. The description can be an SHA1
+checksum, MD5 checksum or any unique value.
+
+The size of these structures varies with the --build-id linker option.
+
## Hypercalls
We will employ the sub operations of the system management hypercall (sysctl).
@@ -867,30 +894,6 @@ This is implemented in the Xen Project hypervisor.
Only the privileged domain should be allowed to do this operation.
-
-# Not Yet Done
-
-This is for further development of xSplice.
-
-## Goals
-
-The implementation must also have a mechanism for:
-
- * An dependency mechanism for the payloads. To use that information to load:
- - The appropiate payload. To verify that payload is built against the
- hypervisor. This can be done via the `build-id`
- or via providing an copy of the old code - so that the hypervisor can
- verify it against the code in memory.
- - To construct an appropiate order of payloads to load in case they
- depend on each other.
- * Be able to lookup in the Xen hypervisor the symbol names of functions from
the ELF payload.
- * Be able to patch .rodata, .bss, and .data sections.
- * Further safety checks (blacklist of which functions cannot be patched, check
- the stack, make sure the payload is built with same compiler as hypervisor,
- and NMI/MCE handlers and do_nmi for right now - until an safe solution is
found).
- * NOP out the code sequence if `new_size` is zero.
- * Deal with other relocation types: R_X86_64_[8,16,32,32S],
R_X86_64_PC[8,16,64] in payload file.
-
### xSplice interdependencies
xSplice patches interdependencies are tricky.
@@ -917,6 +920,33 @@ being loaded and requires an hypervisor build-id to match
against.
The old code allows much more flexibility and an additional guard,
but is more complex to implement.
+The second option which requires an build-id of the hypervisor
+is implemented in the Xen Project hypervisor.
+
+Specifically each payload has two build-id ELF notes:
+ * The build-id of the payload itself (generated via --build-id).
+ * The build-id of the payload it depends on (extracted from the
+ the previous payload or hypervisor during build time).
+
+This means that the very first payload depends on the hypervisor
+build-id.
+
+# Not Yet Done
+
+This is for further development of xSplice.
+
+## Goals
+
+The implementation must also have a mechanism for:
+
+ * Be able to lookup in the Xen hypervisor the symbol names of functions from
the ELF payload.
+ * Be able to patch .rodata, .bss, and .data sections.
+ * Further safety checks (blacklist of which functions cannot be patched, check
+ the stack, make sure the payload is built with same compiler as hypervisor,
+ and NMI/MCE handlers and do_nmi for right now - until an safe solution is
found).
+ * NOP out the code sequence if `new_size` is zero.
+ * Deal with other relocation types: R_X86_64_[8,16,32,32S],
R_X86_64_PC[8,16,64] in payload file.
+
### Handle inlined __LINE__
This problem is related to hotpatch construction
diff --git a/xen/arch/x86/test/Makefile b/xen/arch/x86/test/Makefile
index 45df301..a84c609 100644
--- a/xen/arch/x86/test/Makefile
+++ b/xen/arch/x86/test/Makefile
@@ -7,13 +7,16 @@ CODE_SZ=$(shell nm --defined -S $(1) | grep $(2) | awk '{
print "0x"$$2}')
ifdef CONFIG_XSPLICE
XSPLICE := xen_hello_world.xsplice
+XSPLICE_BYE := xen_bye_world.xsplice
default: xsplice
install: xsplice
$(INSTALL_DATA) $(XSPLICE) $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE)
+ $(INSTALL_DATA) $(XSPLICE_BYE) $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE_BYE)
uninstall:
rm -f $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE)
+ rm -f $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE_BYE)
else
default:
install:
@@ -22,7 +25,7 @@ endif
.PHONY: clean
clean::
- rm -f *.o .*.o.d $(XSPLICE) config.h
+ rm -f *.o .*.o.d $(XSPLICE) config.h build_id.o
#
# To compute these values we need the binary files: xen-syms
@@ -34,15 +37,45 @@ clean::
.PHONY: config.h
config.h: OLD_CODE_SZ=$(call CODE_SZ,$(BASEDIR)/xen-syms,xen_extra_version)
config.h: NEW_CODE_SZ=$(call CODE_SZ,$<,xen_hello_world)
-config.h: xen_hello_world_func.o
+config.h: xen_hello_world_func.o xen_bye_world_func.o
(set -e; \
echo "#define NEW_CODE_SZ $(NEW_CODE_SZ)"; \
echo "#define OLD_CODE_SZ $(OLD_CODE_SZ)") > $@
+#
+# This target is only accessible if CONFIG_XSPLICE is defined, which
+# depends on $(build_id_linker) being available. Hence we do not
+# need any checks.
+#
+.PHONY: build_id.o
+build_id.o:
+ $(OBJCOPY) -O binary --only-section=.note $(BASEDIR)/xen-syms $@.bin
+ $(OBJCOPY) -I binary -O elf64-x86-64 -B i386:x86-64 \
+ --rename-section=.data=.xsplice.depends -S $@.bin $@
+ rm -f $@.bin
+
+
+#
+# Extract the build-id of the xen_hello_world.xsplice
+# (which xen_bye_world will depend on).
+#
+.PHONY: hello_world_build_id.o
+hello_world_build_id.o:
+ $(OBJCOPY) -O binary --only-section=.note.gnu.build-id $(XSPLICE) $@.bin
+ $(OBJCOPY) -I binary -O elf64-x86-64 -B i386:x86-64 \
+ --rename-section=.data=.xsplice.depends -S $@.bin $@
+ rm -f $@.bin
+
.PHONY: xsplice
-xsplice: config.h
+xsplice: config.h build_id.o
# 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
+ $(LD) $(LDFLAGS) $(build_id_linker) -r -o $(XSPLICE) \
+ xen_hello_world_func.o xen_hello_world.o build_id.o
+ $(MAKE) -f $(BASEDIR)/Rules.mk xen_bye_world_func.o
+ $(MAKE) -f $(BASEDIR)/Rules.mk xen_bye_world.o
+ $(MAKE) -f $(BASEDIR)/Rules.mk hello_world_build_id.o
+ $(LD) $(LDFLAGS) $(build_id_linker) -r -o $(XSPLICE_BYE) \
+ xen_bye_world_func.o xen_bye_world.o hello_world_build_id.o
diff --git a/xen/arch/x86/test/xen_bye_world.c
b/xen/arch/x86/test/xen_bye_world.c
new file mode 100644
index 0000000..d26641c
--- /dev/null
+++ b/xen/arch/x86/test/xen_bye_world.c
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2016 Oracle and/or its affiliates. All rights reserved.
+ *
+ */
+
+#include <xen/config.h>
+#include <xen/types.h>
+#include <xen/xsplice_patch.h>
+#include <xen/xsplice.h>
+#include "config.h"
+#include <xen/lib.h>
+
+static char xen_bye_world_name[] = "xen_bye_world";
+extern const char *xen_bye_world(void);
+
+/* External symbol. */
+extern const char *xen_extra_version(void);
+
+struct xsplice_patch_func __section(".xsplice.funcs") xsplice_xen_bye_world = {
+ .name = xen_bye_world_name,
+ .new_addr = (unsigned long)(xen_bye_world),
+ .old_addr = (unsigned long)(xen_extra_version),
+ .new_size = NEW_CODE_SZ,
+ .old_size = OLD_CODE_SZ,
+};
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/x86/test/xen_bye_world_func.c
b/xen/arch/x86/test/xen_bye_world_func.c
new file mode 100644
index 0000000..574268c
--- /dev/null
+++ b/xen/arch/x86/test/xen_bye_world_func.c
@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2016 Oracle and/or its affiliates. All rights reserved.
+ *
+ */
+
+#include <xen/config.h>
+#include <xen/types.h>
+#include <asm/nops.h>
+#include <asm/alternative.h>
+
+/* Our replacement function for xen_hello_world. */
+const char *xen_bye_world(void)
+{
+ return "Bye World!";
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index dbe9ccc..d153c4a 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -54,6 +54,10 @@ config HAS_GDBSX
config HAS_IOPORTS
bool
+config HAS_BUILD_ID
+ string
+ option env="XEN_HAS_BUILD_ID"
+
# Enable/Disable kexec support
config KEXEC
bool "kexec support"
@@ -172,6 +176,7 @@ endmenu
config XSPLICE
bool "xSplice live patching support"
default y
+ depends on HAS_BUILD_ID = "y"
---help---
Allows a running Xen hypervisor to be dynamically patched using
binary patches without rebooting. This is primarily used to binarily
diff --git a/xen/common/version.c b/xen/common/version.c
index af87371..50906b1 100644
--- a/xen/common/version.c
+++ b/xen/common/version.c
@@ -70,10 +70,29 @@ const char *xen_deny(void)
/* Defined in linker script. */
extern const Elf_Note __note_gnu_build_id_start[], __note_gnu_build_id_end[];
+int xen_build_id_check(const Elf_Note *n, const void **p, ssize_t *len)
+{
+ /* Check if we really have a build-id. */
+ if ( NT_GNU_BUILD_ID != n->type )
+ return -ENODATA;
+
+ /* Sanity check, name should be "GNU" for ld-generated build-id. */
+ if ( strncmp(ELFNOTE_NAME(n), "GNU", n->namesz) != 0 )
+ return -ENODATA;
+
+ if ( len )
+ *len = n->descsz;
+ if ( p )
+ *p = ELFNOTE_DESC(n);
+
+ return 0;
+}
+
int xen_build_id(const void **p, ssize_t *len)
{
const Elf_Note *n = __note_gnu_build_id_start;
static bool_t checked = 0;
+ int rc;
if ( checked )
{
@@ -89,23 +108,20 @@ int xen_build_id(const void **p, ssize_t *len)
if ( &n[1] > __note_gnu_build_id_end )
return -ENODATA;
- /* Check if we really have a build-id. */
- if ( NT_GNU_BUILD_ID != n->type )
- return -ENODATA;
-
- /* Sanity check, name should be "GNU" for ld-generated build-id. */
- if ( strncmp(ELFNOTE_NAME(n), "GNU", n->namesz) != 0 )
- return -ENODATA;
-
- *len = n->descsz;
- *p = ELFNOTE_DESC(n);
+ rc = xen_build_id_check(n, p, len);
+ if ( !rc )
+ checked = 1;
- checked = 1;
- return 0;
+ return rc;
}
#else
+int xen_build_id_check(const Elf_Note *n, const void **p, ssize_t *len)
+{
+ return -ENODATA;
+}
+
int xen_build_id(const void **p, ssize_t *len)
{
return -ENODATA;
diff --git a/xen/common/xsplice.c b/xen/common/xsplice.c
index effae86..e963ccd 100644
--- a/xen/common/xsplice.c
+++ b/xen/common/xsplice.c
@@ -5,6 +5,7 @@
#include <xen/bug_ex_symbols.h>
#include <xen/cpu.h>
+#include <xen/elf.h>
#include <xen/guest_access.h>
#include <xen/keyhandler.h>
#include <xen/lib.h>
@@ -62,6 +63,8 @@ struct payload {
xsplice_unloadcall_t *unload_funcs; /* load and unload of the payload. */
unsigned int n_load_funcs; /* Nr of the funcs to load and
execute. */
unsigned int n_unload_funcs; /* Nr of funcs to call durung unload.
*/
+ struct xsplice_build_id id; /* ELFNOTE_DESC(.note.gnu.build-id)
of the payload. */
+ struct xsplice_build_id dep; /* ELFNOTE_DESC(.xsplice.depends). */
char name[XEN_XSPLICE_NAME_SIZE + 1];/* Name of it. */
};
@@ -379,7 +382,9 @@ static int check_special_sections(struct payload *payload,
struct xsplice_elf *elf)
{
unsigned int i;
- static const char *const names[] = { ".xsplice.funcs" };
+ static const char *const names[] = { ".xsplice.funcs" ,
+ ".xsplice.depends",
+ ".note.gnu.build-id"};
for ( i = 0; i < ARRAY_SIZE(names); i++ )
{
@@ -398,6 +403,8 @@ static int check_special_sections(struct payload *payload,
return 0;
}
+#define NT_GNU_BUILD_ID 3
+
static int prepare_payload(struct payload *payload,
struct xsplice_elf *elf)
{
@@ -405,6 +412,7 @@ static int prepare_payload(struct payload *payload,
unsigned int i;
struct xsplice_patch_func *f;
struct virtual_region *region;
+ Elf_Note *n;
sec = xsplice_elf_sec_by_name(elf, ".xsplice.funcs");
if ( sec )
@@ -480,6 +488,33 @@ static int prepare_payload(struct payload *payload,
payload->n_unload_funcs = sec->sec->sh_size / (sizeof
*payload->unload_funcs);
}
+ sec = xsplice_elf_sec_by_name(elf, ".note.gnu.build-id");
+ if ( sec )
+ {
+ n = (Elf_Note *)sec->load_addr;
+ if ( sec->sec->sh_size <= sizeof *n )
+ return -EINVAL;
+
+ if ( xen_build_id_check(n, &payload->id.p, &payload->id.len) )
+ return -EINVAL;
+
+ if ( !payload->id.len || !payload->id.p )
+ return -EINVAL;
+ }
+
+ sec = xsplice_elf_sec_by_name(elf, ".xsplice.depends");
+ {
+ n = (Elf_Note *)sec->load_addr;
+ if ( sec->sec->sh_size <= sizeof *n )
+ return -EINVAL;
+
+ if ( xen_build_id_check(n, &payload->dep.p, &payload->dep.len) )
+ return -EINVAL;
+
+ if ( !payload->dep.len || !payload->dep.p )
+ return -EINVAL;
+ }
+
/* Setup the virtual region with proper data. */
region = &payload->bug_ex_region;
region->skip = ignore_region;
@@ -1175,6 +1210,53 @@ void check_for_xsplice_work(void)
}
}
+/*
+ * Only allow dependent payload is applied on top of the correct
+ * build-id.
+ *
+ * This enforces an stacking order - the first payload MUST be against the
+ * hypervisor. The second against the first payload, and so on.
+ *
+ * Unless the 'ignore' parameter is used - in which case we only
+ * check against the hypervisor.
+ */
+static int build_id_dep(struct payload *payload, bool_t ignore)
+{
+ const void *id = NULL;
+ ssize_t len = 0;
+ int rc;
+ const char *name = "hypervisor";
+
+ ASSERT(payload->dep.len && payload->dep.p);
+
+ /* First time user is against hypervisor. */
+ if ( ignore || list_empty(&applied_list) )
+ {
+ rc = xen_build_id(&id, &len);
+ if ( rc )
+ return rc;
+ }
+ else
+ {
+ /* We should be against the last applied one. */
+ struct payload *data = list_last_entry(&applied_list, struct payload,
+ applied_list);
+
+ id = data->id.p;
+ len = data->id.len;
+ name = data->name;
+ }
+
+ if ( payload->dep.len != len ||
+ memcmp(id, payload->dep.p, len) )
+ {
+ dprintk(XENLOG_DEBUG, "%s%s: check against %s build-id failed!\n",
+ XSPLICE, payload->name, name);
+ return -EINVAL;
+ }
+ return 0;
+}
+
static int xsplice_action(xen_sysctl_xsplice_action_t *action)
{
struct payload *data;
@@ -1213,6 +1295,18 @@ static int xsplice_action(xen_sysctl_xsplice_action_t
*action)
case XSPLICE_ACTION_REVERT:
if ( data->state == XSPLICE_STATE_APPLIED )
{
+ struct payload *p = list_last_entry(&applied_list, struct payload,
+ applied_list);
+
+ ASSERT(p);
+ /* We should be the last applied one. */
+ if ( p != data )
+ {
+ dprintk(XENLOG_DEBUG, "%s%s: can't unload. Top is %s!\n",
+ XSPLICE, data->name, p->name);
+ rc = -EBUSY;
+ break;
+ }
data->rc = -EAGAIN;
rc = schedule_work(data, action->cmd, action->timeout);
}
@@ -1221,6 +1315,9 @@ static int xsplice_action(xen_sysctl_xsplice_action_t
*action)
case XSPLICE_ACTION_APPLY:
if ( (data->state == XSPLICE_STATE_CHECKED) )
{
+ rc = build_id_dep(data, 0 /* against top one. */);
+ if ( rc )
+ break;
data->rc = -EAGAIN;
rc = schedule_work(data, action->cmd, action->timeout);
}
@@ -1229,6 +1326,9 @@ static int xsplice_action(xen_sysctl_xsplice_action_t
*action)
case XSPLICE_ACTION_REPLACE:
if ( data->state == XSPLICE_STATE_CHECKED )
{
+ rc = build_id_dep(data, 1 /* against hypervisor. */);
+ if ( rc )
+ break;
data->rc = -EAGAIN;
rc = schedule_work(data, action->cmd, action->timeout);
}
diff --git a/xen/include/xen/version.h b/xen/include/xen/version.h
index a461c85..bc92370 100644
--- a/xen/include/xen/version.h
+++ b/xen/include/xen/version.h
@@ -16,4 +16,7 @@ const char *xen_deny(void);
#include <xen/types.h>
int xen_build_id(const void **p, ssize_t *len);
+#include <xen/elfstructs.h>
+int xen_build_id_check(const Elf_Note *n, const void **p, ssize_t *len);
+
#endif /* __XEN_VERSION_H__ */
diff --git a/xen/include/xen/xsplice.h b/xen/include/xen/xsplice.h
index 16d35b8..82b20ca 100644
--- a/xen/include/xen/xsplice.h
+++ b/xen/include/xen/xsplice.h
@@ -40,6 +40,11 @@ struct xsplice_symbol {
bool_t new_symbol;
};
+struct xsplice_build_id {
+ const void *p;
+ ssize_t len;
+};
+
int xsplice_op(struct xen_sysctl_xsplice_op *);
void check_for_xsplice_work(void);
bool_t is_patch(const void *addr);
--
2.5.0
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