firmware: Initialize stack guard via Zkr

[Anup Patel]

On Mon, Oct 6, 2025 at 1:33 PM Xiang W <wxjstz at 126.com> wrote:
>
> Try to initialize stack protection guard via the zkr extension.
>
> Signed-off-by: Xiang W <wxjstz at 126.com>

The patch subject is lacking the "[PATCH]" prefix otherwise
it looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup

> ---
>  firmware/fw_base.S | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index 5300ecf2..953fba95 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -107,6 +107,30 @@ _bss_zero:
>         add     s4, s4, __SIZEOF_POINTER__
>         blt     s4, s5, _bss_zero
>
> +       /* Trying to initialize the stack guard via the Zkr extension */
> +       lla     t0, __stack_chk_guard_done
> +       csrw    CSR_MTVEC, t0
> +       li      t0, 0
> +       li      t3, 2
> +       li      t4, 0xffff
> +       li      t5, __SIZEOF_POINTER__
> +__stack_chk_guard_loop:
> +       csrrw   t1, CSR_SEED, x0
> +       srli    t2, t1, 30
> +       andi    t2, t2, 3
> +       bgt     t2, t3, __stack_chk_guard_done
> +       blt     t2, t3, __stack_chk_guard_loop
> +       and     t1, t1, t4
> +       slli    t0, t0, 16
> +       or      t0, t0, t1
> +       addi    t5, t5, -2
> +       bgtz    t5, __stack_chk_guard_loop
> +       lla     t1, __stack_chk_guard
> +       REG_S   t0, 0(t1)
> +       j       __stack_chk_guard_done
> +       .align 3
> +__stack_chk_guard_done:
> +
>         /* Setup temporary trap handler */
>         lla     s4, _start_hang
>         csrw    CSR_MTVEC, s4
> --
> 2.47.3
>