From 9c2598d43510eff09c658f9c0e0f921ba1871c4b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= <bjorn@rivosinc.com>
Date: Mon, 3 Apr 2023 08:52:07 +0200
Subject: [PATCH] riscv: entry: Save a0 prior syscall_enter_from_user_mode()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
The RISC-V calling convention passes the first argument, and the
return value in the a0 register. For this reason, the a0 register
needs some extra care; When handling syscalls, the a0 register is
saved into regs->orig_a0, so a0 can be properly restored for,
e.g. interrupted syscalls.
This functionality was broken with the introduction of the generic
entry patches. Here, a0 was saved into orig_a0 after calling
syscall_enter_from_user_mode(), which can change regs->a0 for some
paths, incorrectly restoring a0.
This is resolved, by saving a0 prior doing the
syscall_enter_from_user_mode() call.
Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20230403065207.1070974-1-bjorn@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
arch/riscv/kernel/traps.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 1f4e37be7eb38..8c258b78c925c 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -270,11 +270,11 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
if (user_mode(regs)) {
ulong syscall = regs->a7;
- syscall = syscall_enter_from_user_mode(regs, syscall);
-
regs->epc += 4;
regs->orig_a0 = regs->a0;
+ syscall = syscall_enter_from_user_mode(regs, syscall);
+
if (syscall < NR_syscalls)
syscall_handler(regs, syscall);
else
--
GitLab