x86: return modified setup_data only if read as memory, not as file

If setup_data is being read into a specific memory location, then
generally the setup_data address parameter is read first, so that the
caller knows where to read it into. In that case, we should return
setup_data containing the absolute addresses that are hard coded and
determined a priori. This is the case when kernels are loaded by BIOS,
for example. In contrast, when setup_data is read as a file, then we
shouldn't modify setup_data, since the absolute address will be wrong by
definition. This is the case when OVMF loads the image.

This allows setup_data to be used like normal, without crashing when EFI
tries to use it.

(As a small development note, strangely, fw_cfg_add_file_callback() was
exported but fw_cfg_add_bytes_callback() wasn't, so this makes that
consistent.)

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Laurent Vivier <laurent@vivier.eu>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Message-Id: <20220921093134.2936487-1-Jason@zx2c4.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
index 0e7a8bc7af..e4fef393be 100644
--- a/include/hw/nvram/fw_cfg.h
+++ b/include/hw/nvram/fw_cfg.h
@@ -118,6 +118,28 @@ struct FWCfgMemState {
 void fw_cfg_add_bytes(FWCfgState *s, uint16_t key, void *data, size_t len);
 
 /**
+ * fw_cfg_add_bytes_callback:
+ * @s: fw_cfg device being modified
+ * @key: selector key value for new fw_cfg item
+ * @select_cb: callback function when selecting
+ * @write_cb: callback function after a write
+ * @callback_opaque: argument to be passed into callback function
+ * @data: pointer to start of item data
+ * @len: size of item data
+ * @read_only: is file read only
+ *
+ * Add a new fw_cfg item, available by selecting the given key, as a raw
+ * "blob" of the given size. The data referenced by the starting pointer
+ * is only linked, NOT copied, into the data structure of the fw_cfg device.
+ */
+void fw_cfg_add_bytes_callback(FWCfgState *s, uint16_t key,
+                               FWCfgCallback select_cb,
+                               FWCfgWriteCallback write_cb,
+                               void *callback_opaque,
+                               void *data, size_t len,
+                               bool read_only);
+
+/**
  * fw_cfg_add_string:
  * @s: fw_cfg device being modified
  * @key: selector key value for new fw_cfg item