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

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Message-ID: <CAJF2gTR2pDN8vvknmE2s1nj2WSuCfTkXYkU074rCck+CCwQv7Q@mail.gmail.com>
Date:   Mon, 20 Dec 2021 21:40:51 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Ard Biesheuvel <ardb@...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, Dec 20, 2021 at 5:17 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> 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
Oh, thx for the link.

>
>
>
>
> > 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/



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/