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

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Date:   Mon, 20 Dec 2021 10:17:20 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     Alexandre Ghiti <alexandre.ghiti@...onical.com>,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Zong Li <zong.li@...ive.com>, Anup Patel <anup@...infault.org>,
        Atish Patra <Atish.Patra@...osinc.com>,
        Christoph Hellwig <hch@....de>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Mayuresh Chitale <mchitale@...tanamicro.com>,
        panqinglin2020@...as.ac.cn,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 12/13] riscv: Initialize thread pointer before calling
 C functions

On Mon, 20 Dec 2021 at 10:11, Guo Ren <guoren@...nel.org> wrote:
>
> On Tue, Dec 7, 2021 at 11:55 AM Alexandre Ghiti
> <alexandre.ghiti@...onical.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@...onical.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/