[PATCH 07/14] powerpc: Add support for restartable sequences
peterz at infradead.org
Thu May 17 17:43:14 AEST 2018
On Thu, May 17, 2018 at 09:19:49AM +0800, Boqun Feng wrote:
> On Wed, May 16, 2018 at 04:13:16PM -0400, Mathieu Desnoyers wrote:
> > and that x86 calls it from syscall_return_slowpath() (which AFAIU is
> > now used in the fast-path since KPTI), I wonder where we should call
> So we actually detect this after the syscall takes effect, right? I
> wonder whether this could be problematic, because "disallowing syscall"
> in rseq areas may means the syscall won't take effect to some people, I
It doesn't really matter I suspect, the important part is the program
I agree that doing it on sysenter is slightly nicer, but I'll take
sysexit if that's what it takes.
> > this on PowerPC ? I was under the impression that PowerPC return to
> > userspace fast-path was not calling C code unless work flags were set,
> > but I might be wrong.
> I think you're right. So we have to introduce callsite to rseq_syscall()
> in syscall path, something like:
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 51695608c68b..a25734a96640 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -222,6 +222,9 @@ system_call_exit:
> mtmsrd r11,1
> #endif /* CONFIG_PPC_BOOK3E */
> + addi r3,r1,STACK_FRAME_OVERHEAD
> + bl rseq_syscall
> ld r9,TI_FLAGS(r12)
> li r11,-MAX_ERRNO
> andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
> But I think it's important for us to first decide where (before or after
> the syscall) we do the detection.
The important thing is the processed getting very dead. Either sysenter
or sysexit gets that done.
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