Re: [PATCH V4 4/8] riscv: traps: Add noinstr to prevent instrumentation inserted

Guo Ren
2022-09-10T12:46:33Z

On Sat, Sep 10, 2022 at 5:17 PM Guo Ren <guoren@kernel.org> wrote:
>
> On Thu, Sep 8, 2022 at 3:34 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Wed, Sep 07, 2022 at 10:25:02PM -0400, guoren@kernel.org wrote:
> > > From: Guo Ren <guoren@linux.alibaba.com>
> > >
> > > Without noinstr the compiler is free to insert instrumentation (think
> > > all the k*SAN, KCov, GCov, ftrace etc..) which can call code we're not
> > > yet ready to run this early in the entry path, for instance it could
> > > rely on RCU which isn't on yet, or expect lockdep state. (by peterz)
> > >
> > > Link: https://lore.kernel.org/linux-riscv/YxcQ6NoPf3AH0EXe@hirez.programming.kicks-ass.net/raw
> > > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > ---
> > > arch/riscv/kernel/traps.c | 8 ++++----
> > > arch/riscv/mm/fault.c | 2 +-
> > > 2 files changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > > index 635e6ec26938..3ed3dbec250d 100644
> > > --- a/arch/riscv/kernel/traps.c
> > > +++ b/arch/riscv/kernel/traps.c
> > > @@ -97,7 +97,7 @@ static void do_trap_error(struct pt_regs *regs, int signo, int code,
> > > #define __trap_section
> > > #endif
> > > #define DO_ERROR_INFO(name, signo, code, str) \
> > > -asmlinkage __visible __trap_section void name(struct pt_regs *regs) \
> > > +asmlinkage __visible __trap_section void noinstr name(struct pt_regs *regs) \
> >
> > But now you have __trap_section and noinstr both adding a section
> > attribute.
>
> Oops, thx for correcting. Here is my solution.
>
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 635e6ec26938..eba744caa711 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -92,9 +92,11 @@ static void do_trap_error(struct pt_regs *regs, int
> signo, int code,
> }
>
> #if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_RISCV_ALTERNATIVE)
> -#define __trap_section __section(".xip.traps")
> +#define __trap_section \
> + noinline notrace __attribute((__section__(".xip.traps"))) \
> + __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
How about let __section(".xip.traps") replace the __section__(".noinstr.text")?
+#define __trap_section noinstr __attribute(__section(".xip.traps"))

> #else
> -#define __trap_section
> +#define __trap_section noinstr
> #endif
>
>
> --
> Best Regards
> Guo Ren

--
Best Regards
Guo Ren