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, 6 insertions, 6 deletions

diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index d605f3f45a..564bda3395 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -692,12 +692,12 @@ static const VMStateDescription vmstate_fw_cfg = {
     }
 };
 
-static 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)
+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)
 {
     int arch = !!(key & FW_CFG_ARCH_LOCAL);