linux-kernel - [PATCH 5.14 024/151] csky: Fixup regs.sr broken in ptrace

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Date:   Mon, 18 Oct 2021 15:23:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH 5.14 024/151] csky: Fixup regs.sr broken in ptrace

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

commit af89ebaa64de726ca0a39bbb0bf0c81a1f43ad50 upstream.

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>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/csky/kernel/ptrace.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/csky/kernel/ptrace.c
+++ b/arch/csky/kernel/ptrace.c
@@ -99,7 +99,8 @@ static int gpr_set(struct task_struct *t
 	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