Re: [PATCH for-6.1] hw/arm/boot: Report error if there is no fw_cfg device in the machine

[Philippe Mathieu-Daudé]

On 7/26/21 6:33 PM, Peter Maydell wrote:
> If the user provides both a BIOS/firmware image and also a guest
> kernel filename, arm_setup_firmware_boot() will pass the
> kernel image to the firmware via the fw_cfg device. However we
> weren't checking whether there really was a fw_cfg device present,
> and if there wasn't we would crash.
> 
> This crash can be provoked with a command line such as
>  qemu-system-aarch64 -M raspi3 -kernel /dev/null -bios /dev/null -display none
> 
> It is currently only possible on the raspi3 machine, because unless
> the machine sets info->firmware_loaded we won't call
> arm_setup_firmware_boot(), and the only machines which set that are:
>  * virt (has a fw-cfg device)
>  * sbsa-ref (checks itself for kernel_filename && firmware_loaded)
>  * raspi3 (crashes)
> 
> But this is an unfortunate beartrap to leave for future machine
> model implementors, so we should handle this situation in boot.c.
> 
> Check in arm_setup_firmware_boot() whether the fw-cfg device exists
> before trying to load files into it, and if it doesn't exist then
> exit with a hopefully helpful error message.
> 
> Because we now handle this check in a machine-agnostic way, we
> can remove the check from sbsa-ref.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/503
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I didn't reuse exactly the same wording sbsa-ref used to have,
> because the bit about loading an OS from hard disk might not
> apply to all machine types.
> ---
>  hw/arm/boot.c     | 9 +++++++++
>  hw/arm/sbsa-ref.c | 7 -------
>  2 files changed, 9 insertions(+), 7 deletions(-)

Thanks for fixing this.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>