[SeaBIOS] [PATCH v5 3/5] QEMU fw_cfg: Add command to write back address of file

From: Ben Warren

This command is similar to ADD_POINTER, but instead of patching
memory, it writes the pointer back to QEMU over the DMA interface.

Signed-off-by: Ben Warren 
---
 src/fw/romfile_loader.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 src/fw/romfile_loader.h | 23 ++++++++++++++++++++---
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/src/fw/romfile_loader.c b/src/fw/romfile_loader.c
index 7737453..30e7b58 100644
--- a/src/fw/romfile_loader.c
+++ b/src/fw/romfile_loader.c
@@ -5,6 +5,7 @@
 #include "romfile.h" // struct romfile_s
 #include "malloc.h" // Zone*, _malloc
 #include "output.h" // warn_*
+#include "paravirt.h" // qemu_cfg_write_file

struct romfile_loader_file {
     struct romfile_s *file;
@@ -127,6 +128,46 @@ err:
     warn_internalerror();
 }

+static void romfile_loader_write_pointer(struct romfile_loader_entry_s *entry,
+                                         struct romfile_loader_files *files)
+{
+    struct romfile_s *dest_file;
+    struct romfile_loader_file *src_file;
+    unsigned dst_offset = le32_to_cpu(entry->wr_pointer.dst_offset);
+    unsigned src_offset = le32_to_cpu(entry->wr_pointer.src_offset);
+    u64 pointer = 0;
+
+    /* Writing back to a file that may not be loaded in RAM */
+    dest_file = romfile_find(entry->wr_pointer.dest_file);
+    src_file = romfile_loader_find(entry->wr_pointer.src_file, files);
+
+    if (!dest_file || !src_file || !src_file->data ||
+        dst_offset + entry->wr_pointer.size < dst_offset ||
+        dst_offset + entry->wr_pointer.size > dest_file->size ||
+        src_offset >= src_file->file->size ||
+        entry->wr_pointer.size < 1 || entry->wr_pointer.size > 8 ||
+        entry->wr_pointer.size & (entry->wr_pointer.size - 1)) {
+        goto err;
+    }
+
+    pointer = (unsigned long)src_file->data + src_offset;
+    /* Make sure the pointer fits within wr_pointer.size */
+    if ((entry->wr_pointer.size != sizeof(u64)) &&
+        ((pointer >> (entry->wr_pointer.size * 8)) > 0)) {
+        goto err;
+    }
+    pointer = cpu_to_le64(pointer);
+
+    /* Only supported on QEMU */
+    if (qemu_cfg_write_file(&pointer, dest_file, dst_offset,
+                            entry->wr_pointer.size) != entry->wr_pointer.size) {
+        goto err;
+    }
+    return;
+ err:
+    warn_internalerror();
+}
+
 int romfile_loader_execute(const char *name)
 {
     struct romfile_loader_entry_s *entry;
@@ -161,6 +202,10 @@ int romfile_loader_execute(const char *name)
                         break;
                 case ROMFILE_LOADER_COMMAND_ADD_CHECKSUM:
                         romfile_loader_add_checksum(entry, files);
+                        break;
+                case ROMFILE_LOADER_COMMAND_WRITE_POINTER:
+                        romfile_loader_write_pointer(entry, files);
+                        break;
                 default:
                         /* Skip commands that we don't recognize. */
                         break;
diff --git a/src/fw/romfile_loader.h b/src/fw/romfile_loader.h
index bce3719..4dc50ab 100644
--- a/src/fw/romfile_loader.h
+++ b/src/fw/romfile_loader.h
@@ -51,15 +51,32 @@ struct romfile_loader_entry_s {
             u32 length;
         } cksum;

+        /*
+         * COMMAND_WRITE_POINTER - Write back to a host file via DMA,
+         * @wr_pointer.dest_file at offset @wr_pointer.dst_offset, a pointer
+         * to the table originating from @wr_pointer.src_file at offset
+         * @wr_pointer.src_offset.
+         * 1,2,4 or 8 byte unsigned addition is used depending on
+         * @wr_pointer.size.
+         */
+        struct {
+            char dest_file[ROMFILE_LOADER_FILESZ];
+            char src_file[ROMFILE_LOADER_FILESZ];
+            u32 dst_offset;
+            u32 src_offset;
+            u8 size;
+        } wr_pointer;
+
         /* padding */
         char pad[124];
     };
 };

enum {
-    ROMFILE_LOADER_COMMAND_ALLOCATE     = 0x1,
-    ROMFILE_LOADER_COMMAND_ADD_POINTER  = 0x2,
-    ROMFILE_LOADER_COMMAND_ADD_CHECKSUM = 0x3,
+    ROMFILE_LOADER_COMMAND_ALLOCATE      = 0x1,
+    ROMFILE_LOADER_COMMAND_ADD_POINTER   = 0x2,
+    ROMFILE_LOADER_COMMAND_ADD_CHECKSUM  = 0x3,
+    ROMFILE_LOADER_COMMAND_WRITE_POINTER = 0x4,
 };

enum {