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Re: [PATCH for-6.1] hw/arm/boot: Report error if there is no fw_cfg devi

From: Richard Henderson
Subject: Re: [PATCH for-6.1] hw/arm/boot: Report error if there is no fw_cfg device in the machine
Date: Mon, 26 Jul 2021 13:08:00 -1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 7/26/21 6:33 AM, 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.

Signed-off-by: Peter Maydell<peter.maydell@linaro.org>

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


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