Uniquely identify the PVH note header

According to Linux kernel documentation:
Each note has three parts: a name, a type and a desc.  The name is
intended to distinguish the note's originator, so it would be a
company, project, subsystem, etc; it must be in a suitable form for
use in a section name.  The type is an integer which is used to tag
the data, and is considered to be within the "name" namespace (so
"FooCo"'s type 42 is distinct from "BarProj"'s type 42).  The
"desc" field is the actual data.  There are no constraints on the
desc field's contents, though typically they're fairly small.

So check both name and type when searching for the PVH note.

Signed-off-by: Liu Jiang <gerry@linux.alibaba.com>

Author: jiangliu

src/loader/x86_64/elf/mod.rs

@@ -249,6 +249,9 @@ impl KernelLoader for Elf {
     }
 }
 
+// Size of string "Xen", including the terminating NULL.
+const PVH_NOTE_STR_SZ: usize = 4;
+
 /// Examines a supplied elf program header of type `PT_NOTE` to determine if it contains an entry
 /// of type `XEN_ELFNOTE_PHYS32_ENTRY` (0x12). Notes of this type encode a physical 32-bit entry
 /// point address into the kernel, which is used when launching guests in 32-bit (protected) mode
@@ -281,11 +284,17 @@ where
             .read_from(0, kernel_image, nhdr_sz)
             .map_err(|_| Error::ReadNoteHeader)?;
 
-        // If the note header found is not the desired one, keep reading until the end of the
-        // segment.
-        if nhdr.n_type == XEN_ELFNOTE_PHYS32_ENTRY {
-            break;
+        // Check if the note header's name and type match the ones specified by the PVH ABI.
+        if nhdr.n_type == XEN_ELFNOTE_PHYS32_ENTRY && nhdr.n_namesz as usize == PVH_NOTE_STR_SZ {
+            let mut buf = [0u8; PVH_NOTE_STR_SZ];
+            kernel_image
+                .read_exact(&mut buf)
+                .map_err(|_| Error::ReadNoteHeader)?;
+            if buf == [b'X', b'e', b'n', b'\0'] {
+                break;
+            }
         }
+
         // Skip the note header plus the size of its fields (with alignment).
         read_size += nhdr_sz
             + align_up(u64::from(nhdr.n_namesz), n_align)
@@ -306,7 +315,7 @@ where
     // just skip the name field contents.
     kernel_image
         .seek(SeekFrom::Current(
-            align_up(u64::from(nhdr.n_namesz), n_align) as i64,
+            align_up(u64::from(nhdr.n_namesz), n_align) as i64 - PVH_NOTE_STR_SZ as i64,
         ))
         .map_err(|_| Error::SeekNoteHeader)?;