Re: [PATCH v3 1/2] RISC-V: Add support for restartable sequence

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Mar 1, 2022, at 9:30 PM, Vincent Chen vincent.chen@sifive.com wrote:

> Add calls to rseq_signal_deliver() and rseq_syscall() to introduce RSEQ
> support.
> 
> 1. Call the rseq_signal_deliver() function to fixup on the pre-signal
>   frame when a signal is delivered on top of a restartable sequence
>   critical section.
> 
> 2. Check that system calls are not invoked from within rseq critical
>   sections by invoking rseq_signal() from ret_from_syscall(). With
>   CONFIG_DEBUG_RSEQ, such behavior results in termination of the
>   process with SIGSEGV.
> 
> Signed-off-by: Vincent Chen <vincent.chen@sifive.com>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Will it be picked by by riscv maintainers ?

Thanks,

Mathieu

> ---
> arch/riscv/Kconfig         | 1 +
> arch/riscv/kernel/entry.S  | 4 ++++
> arch/riscv/kernel/signal.c | 2 ++
> 3 files changed, 7 insertions(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 5adcbd9b5e88..67a671b099b6 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -101,6 +101,7 @@ config RISCV
> 	select HAVE_FUNCTION_ARG_ACCESS_API
> 	select HAVE_STACKPROTECTOR
> 	select HAVE_SYSCALL_TRACEPOINTS
> +	select HAVE_RSEQ
> 	select IRQ_DOMAIN
> 	select IRQ_FORCED_THREADING
> 	select MODULES_USE_ELF_RELA if MODULES
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index ed29e9c8f660..56ada2a583fa 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -225,6 +225,10 @@ ret_from_syscall:
> 	 * (If it was configured with SECCOMP_RET_ERRNO/TRACE)
> 	 */
> ret_from_syscall_rejected:
> +#ifdef CONFIG_DEBUG_RSEQ
> +	move a0, sp
> +	call rseq_syscall
> +#endif
> 	/* Trace syscalls, but only if requested by the user. */
> 	REG_L t0, TASK_TI_FLAGS(tp)
> 	andi t0, t0, _TIF_SYSCALL_WORK
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index c2d5ecbe5526..16da3c3b53a1 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -258,6 +258,8 @@ static void handle_signal(struct ksignal *ksig, struct
> pt_regs *regs)
> 		}
> 	}
> 
> +	rseq_signal_deliver(ksig, regs);
> +
> 	/* Set up the stack frame */
> 	ret = setup_rt_frame(ksig, oldset, regs);
> 
> --
> 2.17.1

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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