[PATCH v1 3/4] XENVER_build_id: Provide ld-embedded build-ids

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

From: Martin Pohlack <mpohlack@amazon.de>

The mechanism to get this is via the XENVER_build_id and
we add a new subsequent sub-command to retrieve the
binary build-id. The hypercall allows an arbitrary
size (the buffer and size is provided to the hypervisor).

To make this work with libxc it requires expanding the
hypercall to use a second parameter. We provide an 'raw' version of
xc_version called xc_version_len. The wrapper around it is
xc_version which retains the automatic size detection.

Note that one can also retrieve the value by 'readelf -h xen-syms'.

For EFI builds we re-use the same build-id that the xen-syms
was built with.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Martin Pohlack <mpohlack@amazon.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 tools/flask/policy/policy/modules/xen/xen.te |  1 +
 tools/libxc/include/xenctrl.h                |  2 ++
 tools/libxc/xc_private.c                     | 37 +++++++++++++++-------------
 tools/libxc/xc_private.h                     |  4 ++-
 xen/arch/x86/Makefile                        | 11 +++++----
 xen/arch/x86/xen.lds.S                       |  6 +++++
 xen/common/kernel.c                          | 32 +++++++++++++++++++++++-
 xen/common/version.c                         | 37 ++++++++++++++++++++++++++++
 xen/include/public/version.h                 |  9 ++++++-
 xen/include/xen/version.h                    |  1 +
 xen/include/xsm/dummy.h                      |  1 +
 xen/xsm/flask/hooks.c                        |  3 +++
 xen/xsm/flask/policy/access_vectors          |  2 ++
 13 files changed, 121 insertions(+), 25 deletions(-)

diff --git a/tools/flask/policy/policy/modules/xen/xen.te b/tools/flask/policy/policy/modules/xen/xen.te
index d0ad758..98ba4f8 100644
--- a/tools/flask/policy/policy/modules/xen/xen.te
+++ b/tools/flask/policy/policy/modules/xen/xen.te
@@ -68,6 +68,7 @@ allow dom0_t xen_t:xen2 {
     resource_op
     psr_cmt_op
     psr_cat_op
+    version_priv
 };
 allow dom0_t xen_t:xen2 {
     pmu_ctrl
diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 3bfa00b..8e1c0c0 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -1633,6 +1633,8 @@ int xc_sysctl(xc_interface *xch, struct xen_sysctl *sysctl);
 
 int xc_version(xc_interface *xch, int cmd, void *arg);
 
+int xc_version_len(xc_interface *xch, int cmd, void *arg, size_t len);
+
 int xc_flask_op(xc_interface *xch, xen_flask_op_t *op);
 
 /*
diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c
index 7c39897..c12dc34 100644
--- a/tools/libxc/xc_private.c
+++ b/tools/libxc/xc_private.c
@@ -674,11 +674,28 @@ int xc_sysctl(xc_interface *xch, struct xen_sysctl *sysctl)
     return do_sysctl(xch, sysctl);
 }
 
+int xc_version_len(xc_interface *xch, int cmd, void *arg, size_t len)
+{
+    DECLARE_HYPERCALL_BOUNCE(arg, len, XC_HYPERCALL_BUFFER_BOUNCE_OUT);
+    int rc;
+
+    if ( (len != 0) && xc_hypercall_bounce_pre(xch, arg) )
+    {
+        PERROR("Could not bounce buffer for version hypercall");
+        return -ENOMEM;
+    }
+
+    rc = do_xen_version(xch, cmd, HYPERCALL_BUFFER(arg), len);
+
+    if ( len != 0 )
+        xc_hypercall_bounce_post(xch, arg);
+
+    return rc;
+}
+
 int xc_version(xc_interface *xch, int cmd, void *arg)
 {
-    DECLARE_HYPERCALL_BOUNCE(arg, 0, XC_HYPERCALL_BUFFER_BOUNCE_OUT); /* Size unknown until cmd decoded */
     size_t sz;
-    int rc;
 
     switch ( cmd )
     {
@@ -716,21 +733,7 @@ int xc_version(xc_interface *xch, int cmd, void *arg)
         ERROR("xc_version: unknown command %d\n", cmd);
         return -EINVAL;
     }
-
-    HYPERCALL_BOUNCE_SET_SIZE(arg, sz);
-
-    if ( (sz != 0) && xc_hypercall_bounce_pre(xch, arg) )
-    {
-        PERROR("Could not bounce buffer for version hypercall");
-        return -ENOMEM;
-    }
-
-    rc = do_xen_version(xch, cmd, HYPERCALL_BUFFER(arg));
-
-    if ( sz != 0 )
-        xc_hypercall_bounce_post(xch, arg);
-
-    return rc;
+    return xc_version_len(xch, cmd, arg, sz);
 }
 
 unsigned long xc_make_page_below_4G(
diff --git a/tools/libxc/xc_private.h b/tools/libxc/xc_private.h
index 2df1d59..82ac1d4 100644
--- a/tools/libxc/xc_private.h
+++ b/tools/libxc/xc_private.h
@@ -227,7 +227,8 @@ void xc__hypercall_buffer_cache_release(xc_interface *xch);
 
 int do_xen_hypercall(xc_interface *xch, privcmd_hypercall_t *hypercall);
 
-static inline int do_xen_version(xc_interface *xch, int cmd, xc_hypercall_buffer_t *dest)
+static inline int do_xen_version(xc_interface *xch, int cmd,
+                                 xc_hypercall_buffer_t *dest, size_t len)
 {
     DECLARE_HYPERCALL;
     DECLARE_HYPERCALL_BUFFER_ARGUMENT(dest);
@@ -235,6 +236,7 @@ static inline int do_xen_version(xc_interface *xch, int cmd, xc_hypercall_buffer
     hypercall.op     = __HYPERVISOR_xen_version;
     hypercall.arg[0] = (unsigned long) cmd;
     hypercall.arg[1] = HYPERCALL_BUFFER_AS_ARG(dest);
+    hypercall.arg[2] = len;
 
     return do_xen_hypercall(xch, &hypercall);
 }
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 39a8059..7e4140a 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -108,12 +108,13 @@ $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o
 	    $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).0
 	$(NM) -n $(@D)/.$(@F).0 | $(BASEDIR)/tools/symbols >$(@D)/.$(@F).0.S
 	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0.o
-	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
+	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o --build-id=sha1 \
 	    $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
 	$(NM) -n $(@D)/.$(@F).1 | $(BASEDIR)/tools/symbols >$(@D)/.$(@F).1.S
 	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1.o
-	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
+	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o --build-id=sha1 \
 	    $(@D)/.$(@F).1.o -o $@
+	$(OBJCOPY) --only-section=.note.gnu.build-id $@ build_id.o
 	rm -f $(@D)/.$(@F).[0-9]*
 
 EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(LDFLAGS)) --subsystem=10
@@ -128,7 +129,7 @@ $(TARGET).efi: VIRT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A VIR
 $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A ALT_START$$,,p')
 # Don't use $(wildcard ...) here - at least make 3.80 expands this too early!
 $(TARGET).efi: guard = $(if $(shell echo efi/dis* | grep disabled),:)
-$(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o $(BASEDIR)/common/symbols-dummy.o efi/mkreloc
+$(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o $(BASEDIR)/common/symbols-dummy.o efi/mkreloc build_id.o
 	$(foreach base, $(VIRT_BASE) $(ALT_BASE), \
 	          $(guard) $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< efi/relocs-dummy.o \
 	                $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).$(base).0 &&) :
@@ -141,8 +142,8 @@ $(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o $(BASEDIR)/common/symbol
 	$(guard) efi/mkreloc $(foreach base,$(VIRT_BASE) $(ALT_BASE),$(@D)/.$(@F).$(base).1) >$(@D)/.$(@F).1r.S
 	$(guard) $(NM) -n $(@D)/.$(@F).$(VIRT_BASE).1 | $(guard) $(BASEDIR)/tools/symbols >$(@D)/.$(@F).1s.S
 	$(guard) $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o
-	$(guard) $(LD) $(call EFI_LDFLAGS,$(VIRT_BASE)) -T efi.lds -N $< \
-	                $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o -o $@
+	$(guard) $(LD) $(call EFI_LDFLAGS,$(VIRT_BASE)) -T efi.lds --build-id=sha1 -N $< \
+	                $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o build_id.o -o $@
 	if $(guard) false; then rm -f $@; echo 'EFI support disabled'; fi
 	rm -f $(@D)/.$(@F).[0-9]*
 
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 6553cff..c4aabc3 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -67,6 +67,12 @@ SECTIONS
        *(.rodata.*)
   } :text
 
+  .note.gnu.build-id : {
+      __note_gnu_build_id_start = .;
+      *(.note.gnu.build-id)
+      __note_gnu_build_id_end = .;
+  } :text
+
   . = ALIGN(SMP_CACHE_BYTES);
   .data.read_mostly : {
        /* Exception table */
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 7bab8de..48df798 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -229,7 +229,8 @@ void __init do_initcalls(void)
  */
 #define XENVER_CMD_XSM_CHECK    ( (1U << XENVER_compile_info) | \
                                   (1U << XENVER_changeset) | \
-                                  (1U << XENVER_commandline) )
+                                  (1U << XENVER_commandline) | \
+                                  (1U << XENVER_build_id) )
 DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg,
                 unsigned int len)
 {
@@ -367,6 +368,35 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg,
         if ( copy_to_guest(arg, saved_cmdline, ARRAY_SIZE(saved_cmdline)) )
             return -EFAULT;
         return 0;
+
+    case XENVER_build_id:
+    {
+        int rc;
+        char *p = NULL;
+        unsigned int sz = 0;
+
+        if ( guest_handle_is_null(arg) )
+            return -EINVAL;
+
+        if ( len == 0 )
+            return -EINVAL;
+
+        if ( !guest_handle_okay(arg, len) )
+            return -EINVAL;
+
+        rc = xen_build_id(&p, &sz);
+        if ( rc )
+            return rc;
+
+        if ( sz > len )
+            return -ENOMEM;
+
+        if ( copy_to_guest(arg, p, sz) )
+            return -EFAULT;
+
+        return sz;
+    }
+
     }
 
     return -ENOSYS;
diff --git a/xen/common/version.c b/xen/common/version.c
index b152e27..26eeadf 100644
--- a/xen/common/version.c
+++ b/xen/common/version.c
@@ -1,5 +1,9 @@
 #include <xen/compile.h>
 #include <xen/version.h>
+#include <xen/types.h>
+#include <xen/string.h>
+#include <xen/elf.h>
+#include <xen/errno.h>
 
 const char *xen_compile_date(void)
 {
@@ -55,3 +59,36 @@ const char *xen_banner(void)
 {
     return XEN_BANNER;
 }
+
+#ifdef CONFIG_ARM
+int xen_build_id(char **p, unsigned int *len)
+{
+    return -ENODATA;
+}
+#else
+#define NT_GNU_BUILD_ID 3
+
+extern const Elf_Note __note_gnu_build_id_start;  /* Defined in linker script. */
+extern const char __note_gnu_build_id_end[];
+int xen_build_id(char **p, unsigned int *len)
+{
+    const Elf_Note *n = &__note_gnu_build_id_start;
+
+    /* Something is wrong. */
+    if ( __note_gnu_build_id_end <= (char *)&__note_gnu_build_id_start )
+        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);
+
+    return 0;
+}
+#endif
diff --git a/xen/include/public/version.h b/xen/include/public/version.h
index 44f26b0..e575d6b 100644
--- a/xen/include/public/version.h
+++ b/xen/include/public/version.h
@@ -30,7 +30,8 @@
 
 #include "xen.h"
 
-/* NB. All ops return zero on success, except XENVER_{version,pagesize} */
+/* NB. All ops return zero on success, except
+ * XENVER_{version,pagesize, build_id} */
 
 /* arg == NULL; returns major:minor (16:16). */
 #define XENVER_version      0
@@ -83,6 +84,12 @@ typedef struct xen_feature_info xen_feature_info_t;
 #define XENVER_commandline 9
 typedef char xen_commandline_t[1024];
 
+#define XENVER_build_id 10
+/*
+ * arg1 == pointer to char array, arg2 == size of char array.
+ * Return value is the actual size.
+ */
+
 #endif /* __XEN_PUBLIC_VERSION_H__ */
 
 /*
diff --git a/xen/include/xen/version.h b/xen/include/xen/version.h
index 81a3c7d..9584f36 100644
--- a/xen/include/xen/version.h
+++ b/xen/include/xen/version.h
@@ -12,5 +12,6 @@ unsigned int xen_minor_version(void);
 const char *xen_extra_version(void);
 const char *xen_changeset(void);
 const char *xen_banner(void);
+int xen_build_id(char **p, unsigned int *len);
 
 #endif /* __XEN_VERSION_H__ */
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 2ee102e..66bc23e 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -729,6 +729,7 @@ static XSM_INLINE int xsm_version_op (XSM_DEFAULT_ARG uint32_t op)
     case XENVER_compile_info:
     case XENVER_changeset:
     case XENVER_commandline:
+    case XENVER_build_id:
         return xsm_default_action(XSM_PRIV, current->domain, NULL);
     case XENVER_version:
     case XENVER_extraversion:
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 4f1269d..829aaeb 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1631,6 +1631,9 @@ static int flask_version_op (uint32_t op)
     case XENVER_commandline:
         return current_has_perm(current->domain, SECCLASS_DOMAIN2,
                                 DOMAIN2__VERSION_USE);
+    case XENVER_build_id:
+        return avc_has_perm(domain_sid(current->domain), SECINITSID_XEN,
+                            SECCLASS_XEN2, XEN2__VERSION_PRIV, NULL);
     case XENVER_version:
     case XENVER_extraversion:
     case XENVER_capabilities:
diff --git a/xen/xsm/flask/policy/access_vectors b/xen/xsm/flask/policy/access_vectors
index 6e2e5d1..58b75a0 100644
--- a/xen/xsm/flask/policy/access_vectors
+++ b/xen/xsm/flask/policy/access_vectors
@@ -93,6 +93,8 @@ class xen2
     pmu_ctrl
 # PMU use (domains, including unprivileged ones, will be using this operation)
     pmu_use
+# XENVER_build_id and other priv
+    version_priv
 }
 
 # Classes domain and domain2 consist of operations that a domain performs on
-- 
2.1.0