linux-kernel - [PATCH 3/4] riscv: Correct the handling of unexpected ebreak in do_trap

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Date:   Mon, 23 Sep 2019 08:45:16 +0800
From:   Vincent Chen <vincent.chen@...ive.com>
To:     linux-riscv@...ts.infradead.org
Cc:     paul.walmsley@...ive.com, palmer@...ive.com, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org, vincent.chen@...ive.com
Subject: [PATCH 3/4] riscv: Correct the handling of unexpected ebreak in do_trap_break()

For the kernel space, all ebreak instructions are determined at compile
time because the kernel space debugging module is currently unsupported.
Hence, it should be treated as a bug if an ebreak instruction which does
not belong to BUG_TRAP_TYPE_WARN or BUG_TRAP_TYPE_BUG is executed in
kernel space. For the userspace, debugging module or user problem may
intentionally insert an ebreak instruction to trigger a SIGTRAP signal.
To approach the above two situations, the do_trap_break() will direct
the BUG_TRAP_TYPE_NONE ebreak exception issued in kernel space to die()
and will send a SIGTRAP to the trapped process only when the ebreak is
in userspace.

Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
---
 arch/riscv/kernel/traps.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 82f42a55451e..dd13bc90aeb6 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -130,8 +130,6 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
 		type = report_bug(regs->sepc, regs);
 		switch (type) {
 #ifdef CONFIG_GENERIC_BUG
-		case BUG_TRAP_TYPE_NONE:
-			break;
 		case BUG_TRAP_TYPE_WARN:
 			regs->sepc += get_break_insn_length(regs->sepc);
 			return;
@@ -140,8 +138,9 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
 		default:
 			die(regs, "Kernel BUG");
 		}
-	}
-	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc));
+	} else
+		force_sig_fault(SIGTRAP, TRAP_BRKPT,
+				(void __user *)(regs->sepc));
 }

 #ifdef CONFIG_GENERIC_BUG
-- 
2.7.4