[PATCH v3 12/13] riscv: Initialize thread pointer before calling C functions

[Ard Biesheuvel]

On Mon, 20 Dec 2021 at 10:11, Guo Ren <guoren at kernel.org> wrote:
>
> On Tue, Dec 7, 2021 at 11:55 AM Alexandre Ghiti
> <alexandre.ghiti at canonical.com> wrote:
> >
> > Because of the stack canary feature that reads from the current task
> > structure the stack canary value, the thread pointer register "tp" must
> > be set before calling any C function from head.S: by chance, setup_vm
> Shall we disable -fstack-protector for setup_vm() with __attribute__?

Don't use __attribute__((optimize())) for that: it is known to be
broken, and documented as debug purposes only in the GCC info pages:

https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html




> Actually, we've already init tp later.
>
> > and all the functions that it calls does not seem to be part of the
> > functions where the canary check is done, but in the following commits,
> > some functions will.
> >
> > Fixes: f2c9699f65557a31 ("riscv: Add STACKPROTECTOR supported")
> > Signed-off-by: Alexandre Ghiti <alexandre.ghiti at canonical.com>
> > ---
> >  arch/riscv/kernel/head.S | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index c3c0ed559770..86f7ee3d210d 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -302,6 +302,7 @@ clear_bss_done:
> >         REG_S a0, (a2)
> >
> >         /* Initialize page tables and relocate to virtual addresses */
> > +       la tp, init_task
> >         la sp, init_thread_union + THREAD_SIZE
> >         XIP_FIXUP_OFFSET sp
> >  #ifdef CONFIG_BUILTIN_DTB
> > --
> > 2.32.0
> >
>
>
> --
> Best Regards
>  Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/