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

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Date:   Fri, 4 Oct 2019 11:28:23 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Vincent Chen <vincent.chen@...ive.com>
cc:     linux-riscv@...ts.infradead.org, palmer@...ive.com,
        aou@...s.berkeley.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] riscv: Correct the handling of unexpected ebreak in
 do_trap_break()

On Mon, 23 Sep 2019, Vincent Chen wrote:

> 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>

Thanks, queued the following for v5.4-rc.


- Paul

From: Vincent Chen <vincent.chen@...ive.com>
Date: Mon, 23 Sep 2019 08:45:16 +0800
Subject: [PATCH] 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>
Reviewed-by: Christoph Hellwig <hch@....de>
[paul.walmsley@...ive.com: fixed checkpatch issue]
Signed-off-by: Paul Walmsley <paul.walmsley@...ive.com>
---
 arch/riscv/kernel/traps.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 82f42a55451e..93742df9067f 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 +138,10 @@ asmlinkage void do_trap_break(struct pt_regs *regs)
 		default:
 			die(regs, "Kernel BUG");
 		}
+	} else {
+		force_sig_fault(SIGTRAP, TRAP_BRKPT,
+				(void __user *)(regs->sepc));
 	}
-	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)(regs->sepc));
 }
 
 #ifdef CONFIG_GENERIC_BUG
-- 
2.23.0