boot: Read files in small chunks on broken firmware

Fixes: #25911

src/boot/efi/boot.c

@@ -2311,12 +2311,13 @@ static EFI_STATUS initrd_prepare(
                 if (info->FileSize == 0) /* Automatically skip over empty files */
                         continue;
 
-                size_t new_size, read_size = info->FileSize;
-                if (__builtin_add_overflow(size, read_size, &new_size))
+                size_t new_size, read_size;
+                if (__builtin_add_overflow(size, info->FileSize, &new_size))
                         return EFI_OUT_OF_RESOURCES;
                 initrd = xrealloc(initrd, size, new_size);
 
-                err = handle->Read(handle, &read_size, initrd + size);
+                void *read_buf = initrd + size;
+                err = file_read(root, *i, 0, info->FileSize, &read_buf, &read_size);
                 if (err != EFI_SUCCESS)
                         return err;
 

src/boot/efi/util.c

@@ -333,9 +333,46 @@ EFI_STATUS file_read(EFI_FILE *dir, const char16_t *name, size_t off, size_t siz
         }
 
         err = handle->Read(handle, &size, read_buf);
-        if (err != EFI_SUCCESS)
+        if (!IN_SET(err, EFI_SUCCESS, EFI_BAD_BUFFER_SIZE))
                 return err;
 
+        /* Some firmwares cannot handle large file reads and will instead return EFI_BAD_BUFFER_SIZE.
+         * As a workaround, read such files in small chunks.
+         *
+         * https://github.com/systemd/systemd/issues/25911 */
+        if (err == EFI_BAD_BUFFER_SIZE) {
+                /* Handle is probably in a permanent bad state. Re-open the file. */
+                (void) handle->Close(handle);
+                handle = NULL;
+
+                err = dir->Open(dir, &handle, (char16_t *) name, EFI_FILE_MODE_READ, 0);
+                if (err != EFI_SUCCESS)
+                        return err;
+
+                if (off > 0) {
+                        err = handle->SetPosition(handle, off);
+                        if (err != EFI_SUCCESS)
+                                return err;
+                }
+
+                size_t remaining = size;
+                size = 0;
+                while (remaining > 0) {
+                        size_t chunk = MIN(1024U * 1024U, remaining);
+
+                        err = handle->Read(handle, &chunk, (uint8_t *) read_buf + size);
+                        if (err != EFI_SUCCESS)
+                                return err;
+                        if (chunk == 0)
+                                /* Caller requested more bytes than are in file. */
+                                break;
+
+                        assert(chunk <= remaining);
+                        size += chunk;
+                        remaining -= chunk;
+                }
+        }
+
         if (buf_owned) {
                 /* Note that handle->Read() changes size to reflect the actually bytes read. */
                 memset((uint8_t *) read_buf + size, 0, extra);