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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/10/15 03:56, Konrad Rzeszutek Wilk wrote:

@@ -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;

A NULL guest handle should return size, in the same way that we have size queries with other hypercalls.  In the future, build-id will probably extend to sha256 and get longer as a result.

+
+        if ( len == 0 )
+            return -EINVAL;

This check is redundant with the "sz > len" check below.

+
+        if ( !guest_handle_okay(arg, len) )
+            return -EINVAL;

This check is performed by copy_to_guest() below.

+
+        rc = xen_build_id(&p, &sz);
+        if ( rc )
+            return rc;
+
+        if ( sz > len )
+            return -ENOMEM;

ENOBUFS

+
+        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 Elf_Note __note_gnu_build_id_start[], __note_gnu_build_id_end[];

+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;

const Elf_Note *n = __note_gnu_build_id_start;

+
+    /* Something is wrong. */
+    if ( __note_gnu_build_id_end <= (char *)&__note_gnu_build_id_start )

Need to check for a full Note header as well.

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);

This information could be cached in a couple of static variables, so the sanity checks are only performed once.

+
+    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.

Return value is the number of bytes written, or -ve error.

~Andrew

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