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

From: Ard Biesheuvel <ardb@kernel.org>
To: Guo Ren <guoren@kernel.org>
Cc: Alexandre Ghiti <alexandre.ghiti@canonical.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Zong Li <zong.li@sifive.com>,
	Anup Patel <anup@brainfault.org>,
	Atish Patra <Atish.Patra@rivosinc.com>,
	Christoph Hellwig <hch@lst.de>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>, Arnd Bergmann <arnd@arndb.de>,
	Kees Cook <keescook@chromium.org>,
	Guo Ren <guoren@linux.alibaba.com>,
	Heinrich Schuchardt <heinrich.schuchardt@canonical.com>,
	Mayuresh Chitale <mchitale@ventanamicro.com>,
	panqinglin2020@iscas.ac.cn,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	linux-efi <linux-efi@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v3 12/13] riscv: Initialize thread pointer before calling C functions
Date: Mon, 20 Dec 2021 10:17:20 +0100	[thread overview]
Message-ID: <CAMj1kXHmdDKFozkoAfM-mxsxxfanhVq5HcA1qKTrkp=vAt=Umg@mail.gmail.com> (raw)
In-Reply-To: <CAJF2gTQEHv1dVzv=JNCYSzD8oh6UxYOFRTdBOp-FFeeeOhSJrQ@mail.gmail.com>

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