[PATCH v4 1/2] RISC-V: Add support for restartable sequence

[Vincent Chen]

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