[PATCH v2 1/1] firmware: Initialize stack guard via Zkr

[Xiang W]

在 2025-12-28日的 21:04 +0530，Anup Patel写道：
> On Wed, Dec 10, 2025 at 8:40 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>
> > Reviewed-by: Anup Patel <anup at brainfault.org>
> 
> I think my Reviewed-by was premature previously. Please see
> few comments below.
> 
> > ---
> > v2 changes: add '[PATCH]'
> > 
> >  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
> 
> We have various hard-coded values related to SEED
> CSR over here. Please introduce appropriate defines in
> riscv_encoding.h and use it over here.

Please review at:
https://lists.infradead.org/pipermail/opensbi/2026-January/009301.html

> 
> > +       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
> 
> Should this not be "addi t5, t5, -16" since we are
> reading 16 bits of entropy in one loop iteration ?

t5 is initialized with bytes size, not bits size.

Regards,
Xiang W
> 
> > +       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
> > 
> 
> Regards,
> Anup