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[Xen-devel] [PATCH v2 2/3] XENVER_build_id: Provide ld-embedded build-ids



From: Martin Pohlack <mpohlack@xxxxxxxxx>

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 len is provided to the hypervisor).

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.

Note that there are no changes to the XSM files (dummy.c
and hooks.c) as the priviliged subops fall in the default case.

Since the new sub-ops provides the len parameter in the
arguments to the hypercall we have to modify libxc to allow
copying the arguments before the hypercall. We provide a
new macro that modifies the bounce structure to change
the direction.

Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Martin Pohlack <mpohlack@xxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
v1: Rebase it on Martin's initial patch
v2: Move it to XENVER hypercall
v3: Fix EFI building (Ross's fix)
v4: Don't use the third argument for length.
v5: Use new structure for XENVER_build_id with variable buf.
---
 tools/libxc/xc_private.c            |  7 +++++++
 tools/libxc/xc_private.h            | 10 ++++++++++
 xen/arch/x86/Makefile               | 14 +++++++++-----
 xen/arch/x86/xen.lds.S              |  6 ++++++
 xen/common/kernel.c                 | 29 +++++++++++++++++++++++++++++
 xen/common/version.c                | 36 ++++++++++++++++++++++++++++++++++++
 xen/include/public/version.h        | 15 ++++++++++++++-
 xen/include/xen/version.h           |  1 +
 xen/xsm/flask/policy/access_vectors |  2 +-
 9 files changed, 113 insertions(+), 7 deletions(-)

diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c
index 7c39897..9cd676e 100644
--- a/tools/libxc/xc_private.c
+++ b/tools/libxc/xc_private.c
@@ -712,6 +712,13 @@ int xc_version(xc_interface *xch, int cmd, void *arg)
     case XENVER_commandline:
         sz = sizeof(xen_commandline_t);
         break;
+    case XENVER_build_id:
+        {
+            xen_build_id_t *build_id = (xen_build_id_t *)arg;
+            sz = sizeof(*build_id) + build_id->len;
+            HYPERCALL_BOUNCE_SET_DIR(arg, XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
+            break;
+        }
     default:
         ERROR("xc_version: unknown command %d\n", cmd);
         return -EINVAL;
diff --git a/tools/libxc/xc_private.h b/tools/libxc/xc_private.h
index 2df1d59..aa0cad7 100644
--- a/tools/libxc/xc_private.h
+++ b/tools/libxc/xc_private.h
@@ -202,6 +202,16 @@ enum {
 #define DECLARE_HYPERCALL_BOUNCE(_ubuf, _sz, _dir) 
DECLARE_NAMED_HYPERCALL_BOUNCE(_ubuf, _ubuf, _sz, _dir)
 
 /*
+ * Change the direction.
+ *
+ * Can only be used if the bounce_pre/bounce_post commands have
+ * not been used.
+ */
+#define HYPERCALL_BOUNCE_SET_DIR(_buf, _dir) do { if 
((HYPERCALL_BUFFER(_buf))->hbuf)         \
+                                                        assert(1);             
               \
+                                                   
(HYPERCALL_BUFFER(_buf))->dir = _dir;      \
+                                                } while (0)
+/*
  * Set the size of data to bounce. Useful when the size is not known
  * when the bounce buffer is declared.
  */
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index d4e507a..17a4830 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -109,15 +109,19 @@ $(TARGET)-syms: prelink.o xen.lds 
$(BASEDIR)/common/symbols-dummy.o
        $(NM) -pa --format=sysv $(@D)/.$(@F).0 \
                | $(BASEDIR)/tools/symbols --sysv --sort >$(@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) -pa --format=sysv $(@D)/.$(@F).1 \
                | $(BASEDIR)/tools/symbols --sysv --sort --warn-dup 
>$(@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 $@
        rm -f $(@D)/.$(@F).[0-9]*
 
+build_id.o: $(TARGET)-syms
+       $(OBJCOPY) --only-section=.note.gnu.build-id $< build_id.o
+
+
 EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(LDFLAGS)) --subsystem=10
 EFI_LDFLAGS += --image-base=$(1) --stack=0,0 --heap=0,0 --strip-debug
 EFI_LDFLAGS += --section-alignment=0x200000 --file-alignment=0x20
@@ -130,7 +134,7 @@ $(TARGET).efi: VIRT_BASE = 0x$(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 &&) :
@@ -145,8 +149,8 @@ $(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o 
$(BASEDIR)/common/symbol
        $(guard) $(NM) -pa --format=sysv $(@D)/.$(@F).$(VIRT_BASE).1 \
                | $(guard) $(BASEDIR)/tools/symbols --sysv --sort 
>$(@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 d51a3ed..1574c63 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -366,6 +366,35 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
             return -EFAULT;
         return 0;
     }
+    case XENVER_build_id:
+    {
+        xen_build_id_t build_id;
+        unsigned int sz;
+        int rc = 0;
+        char *p = NULL;
+
+        if ( deny )
+            return -EPERM;
+
+        if ( copy_from_guest(&build_id, arg, 1) )
+            return -EFAULT;
+
+        if ( build_id.len == 0 )
+            return -EINVAL;
+
+        rc = xen_build_id(&p, &sz);
+        if ( rc )
+            return rc;
+
+        if ( sz > build_id.len )
+            return -ENOMEM;
+
+        if ( copy_to_guest_offset(arg, offsetof(xen_build_id_t, buf),
+                                  deny ? xen_deny() : p, sz) )
+            return -EFAULT;
+
+        return sz;
+    }
     }
 
     return -ENOSYS;
diff --git a/xen/common/version.c b/xen/common/version.c
index 786be4e..d556c35 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)
 {
@@ -60,3 +64,35 @@ const char *xen_deny(void)
 {
     return "<denied>";
 }
+#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..adae298 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 +84,18 @@ typedef struct xen_feature_info xen_feature_info_t;
 #define XENVER_commandline 9
 typedef char xen_commandline_t[1024];
 
+/* arg = xen_build_id_t. Returns size in bytes or XEN_Exx. */
+#define XENVER_build_id 10
+struct xen_build_id {
+        uint32_t        len; /* IN: size of buf[]. */
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
+        unsigned char   buf[];
+#elif defined(__GNUC__)
+        unsigned char   buf[1]; /* OUT: Variable length buffer with build_id. 
*/
+#endif
+};
+typedef struct xen_build_id xen_build_id_t;
+
 #endif /* __XEN_PUBLIC_VERSION_H__ */
 
 /*
diff --git a/xen/include/xen/version.h b/xen/include/xen/version.h
index 2015c0b..466c977 100644
--- a/xen/include/xen/version.h
+++ b/xen/include/xen/version.h
@@ -13,5 +13,6 @@ const char *xen_extra_version(void);
 const char *xen_changeset(void);
 const char *xen_banner(void);
 const char *xen_deny(void);
+int xen_build_id(char **p, unsigned int *len);
 
 #endif /* __XEN_VERSION_H__ */
diff --git a/xen/xsm/flask/policy/access_vectors 
b/xen/xsm/flask/policy/access_vectors
index 273459f..35bdb42 100644
--- a/xen/xsm/flask/policy/access_vectors
+++ b/xen/xsm/flask/policy/access_vectors
@@ -93,7 +93,7 @@ class xen2
     pmu_ctrl
 # PMU use (domains, including unprivileged ones, will be using this operation)
     pmu_use
-# XENVER_[compile_info|changeset|commandline|extraversion] usage.
+# XENVER_[compile_info|changeset|commandline|extraversion|buildid] usage.
    version_priv
 }
 
-- 
2.1.0


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