linux-kernel - [PATCH] csky: Fixup regs.sr broken in ptrace

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Date:   Fri, 24 Sep 2021 15:36:45 +0800
From:   guoren@...nel.org
To:     guoren@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-csky@...r.kernel.org,
        Guo Ren <guoren@...ux.alibaba.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH] csky: Fixup regs.sr broken in ptrace

From: Guo Ren <guoren@...ux.alibaba.com>

gpr_get() return the entire pt_regs (include sr) to userspace, if we
don't restore the C bit in gpr_set, it may break the ALU result in
that context. So the C flag bit is part of gpr context, that's why
riscv totally remove the C bit in the ISA. That makes sr reg clear
from userspace to supervisor privilege.

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
---
 arch/csky/kernel/ptrace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/csky/kernel/ptrace.c b/arch/csky/kernel/ptrace.c
index 0105ac81b432..1a5f54e0d272 100644
--- a/arch/csky/kernel/ptrace.c
+++ b/arch/csky/kernel/ptrace.c
@@ -99,7 +99,8 @@ static int gpr_set(struct task_struct *target,
 	if (ret)
 		return ret;
 
-	regs.sr = task_pt_regs(target)->sr;
+	/* BIT(0) of regs.sr is Condition Code/Carry bit */
+	regs.sr = (regs.sr & BIT(0)) | (task_pt_regs(target)->sr & ~BIT(0));
 #ifdef CONFIG_CPU_HAS_HILO
 	regs.dcsr = task_pt_regs(target)->dcsr;
 #endif
-- 
2.25.1