dump: add guest ELF note

Read the guest ELF PT_NOTE from guest memory when fw_cfg
etc/vmcoreinfo entry provides the location, and write it as an
additional note in the dump.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

dump.c

@@ -25,6 +25,8 @@
 #include "qapi/qmp/qerror.h"
 #include "qmp-commands.h"
 #include "qapi-event.h"
+#include "qemu/error-report.h"
+#include "hw/misc/vmcoreinfo.h"
 
 #include <zlib.h>
 #ifdef CONFIG_LZO
@@ -37,6 +39,13 @@
 #define ELF_MACHINE_UNAME "Unknown"
 #endif
 
+#define MAX_GUEST_NOTE_SIZE (1 << 20) /* 1MB should be enough */
+
+#define ELF_NOTE_SIZE(hdr_size, name_size, desc_size)   \
+    ((DIV_ROUND_UP((hdr_size), 4) +                     \
+      DIV_ROUND_UP((name_size), 4) +                    \
+      DIV_ROUND_UP((desc_size), 4)) * 4)
+
 uint16_t cpu_to_dump16(DumpState *s, uint16_t val)
 {
     if (s->dump_info.d_endian == ELFDATA2LSB) {
@@ -75,6 +84,8 @@ static int dump_cleanup(DumpState *s)
     guest_phys_blocks_free(&s->guest_phys_blocks);
     memory_mapping_list_free(&s->list);
     close(s->fd);
+    g_free(s->guest_note);
+    s->guest_note = NULL;
     if (s->resume) {
         if (s->detached) {
             qemu_mutex_lock_iothread();
@@ -234,6 +245,19 @@ static inline int cpu_index(CPUState *cpu)
     return cpu->cpu_index + 1;
 }
 
+static void write_guest_note(WriteCoreDumpFunction f, DumpState *s,
+                             Error **errp)
+{
+    int ret;
+
+    if (s->guest_note) {
+        ret = f(s->guest_note, s->guest_note_size, s);
+        if (ret < 0) {
+            error_setg(errp, "dump: failed to write guest note");
+        }
+    }
+}
+
 static void write_elf64_notes(WriteCoreDumpFunction f, DumpState *s,
                               Error **errp)
 {
@@ -257,6 +281,8 @@ static void write_elf64_notes(WriteCoreDumpFunction f, DumpState *s,
             return;
         }
     }
+
+    write_guest_note(f, s, errp);
 }
 
 static void write_elf32_note(DumpState *s, Error **errp)
@@ -302,6 +328,8 @@ static void write_elf32_notes(WriteCoreDumpFunction f, DumpState *s,
             return;
         }
     }
+
+    write_guest_note(f, s, errp);
 }
 
 static void write_elf_section(DumpState *s, int type, Error **errp)
@@ -713,6 +741,44 @@ static int buf_write_note(const void *buf, size_t size, void *opaque)
     return 0;
 }
 
+/*
+ * This function retrieves various sizes from an elf header.
+ *
+ * @note has to be a valid ELF note. The return sizes are unmodified
+ * (not padded or rounded up to be multiple of 4).
+ */
+static void get_note_sizes(DumpState *s, const void *note,
+                           uint64_t *note_head_size,
+                           uint64_t *name_size,
+                           uint64_t *desc_size)
+{
+    uint64_t note_head_sz;
+    uint64_t name_sz;
+    uint64_t desc_sz;
+
+    if (s->dump_info.d_class == ELFCLASS64) {
+        const Elf64_Nhdr *hdr = note;
+        note_head_sz = sizeof(Elf64_Nhdr);
+        name_sz = tswap64(hdr->n_namesz);
+        desc_sz = tswap64(hdr->n_descsz);
+    } else {
+        const Elf32_Nhdr *hdr = note;
+        note_head_sz = sizeof(Elf32_Nhdr);
+        name_sz = tswap32(hdr->n_namesz);
+        desc_sz = tswap32(hdr->n_descsz);
+    }
+
+    if (note_head_size) {
+        *note_head_size = note_head_sz;
+    }
+    if (name_size) {
+        *name_size = name_sz;
+    }
+    if (desc_size) {
+        *desc_size = desc_sz;
+    }
+}
+
 /* write common header, sub header and elf note to vmcore */
 static void create_header32(DumpState *s, Error **errp)
 {
@@ -1491,6 +1557,7 @@ static void dump_init(DumpState *s, int fd, bool has_format,
                       DumpGuestMemoryFormat format, bool paging, bool has_filter,
                       int64_t begin, int64_t length, Error **errp)
 {
+    VMCoreInfoState *vmci = vmcoreinfo_find();
     CPUState *cpu;
     int nr_cpus;
     Error *err = NULL;
@@ -1568,6 +1635,46 @@ static void dump_init(DumpState *s, int fd, bool has_format,
         goto cleanup;
     }
 
+    /*
+     * The goal of this block is to copy the guest note out of
+     * the guest.  Failure to do so is not fatal for dumping.
+     */
+    if (vmci) {
+        uint64_t addr, note_head_size, name_size, desc_size;
+        uint32_t size;
+        uint16_t format;
+
+        note_head_size = s->dump_info.d_class == ELFCLASS32 ?
+            sizeof(Elf32_Nhdr) : sizeof(Elf64_Nhdr);
+
+        format = le16_to_cpu(vmci->vmcoreinfo.guest_format);
+        size = le32_to_cpu(vmci->vmcoreinfo.size);
+        addr = le64_to_cpu(vmci->vmcoreinfo.paddr);
+        if (!vmci->has_vmcoreinfo) {
+            warn_report("guest note is not present");
+        } else if (size < note_head_size || size > MAX_GUEST_NOTE_SIZE) {
+            warn_report("guest note size is invalid: %" PRIu32, size);
+        } else if (format != VMCOREINFO_FORMAT_ELF) {
+            warn_report("guest note format is unsupported: %" PRIu16, format);
+        } else {
+            s->guest_note = g_malloc(size + 1); /* +1 for adding \0 */
+            cpu_physical_memory_read(addr, s->guest_note, size);
+
+            get_note_sizes(s, s->guest_note, NULL, &name_size, &desc_size);
+            s->guest_note_size = ELF_NOTE_SIZE(note_head_size, name_size,
+                                               desc_size);
+            if (name_size > MAX_GUEST_NOTE_SIZE ||
+                desc_size > MAX_GUEST_NOTE_SIZE ||
+                s->guest_note_size > size) {
+                warn_report("Invalid guest note header");
+                g_free(s->guest_note);
+                s->guest_note = NULL;
+            } else {
+                s->note_size += s->guest_note_size;
+            }
+        }
+    }
+
     /* get memory mapping */
     if (paging) {
         qemu_get_guest_memory_mapping(&s->list, &s->guest_phys_blocks, &err);

include/sysemu/dump.h

@@ -192,6 +192,8 @@ typedef struct DumpState {
                                   * this could be used to calculate
                                   * how much work we have
                                   * finished. */
+    uint8_t *guest_note;         /* ELF note content */
+    size_t guest_note_size;
 } DumpState;
 
 uint16_t cpu_to_dump16(DumpState *s, uint16_t val);