linux-kernel - [PATCH v3 3/7] riscv: Fixup kprobes handler couldn't change pc

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Date:   Mon, 13 Jul 2020 23:39:18 +0000
From:   guoren@...nel.org
To:     palmerdabbelt@...gle.com, paul.walmsley@...ive.com,
        mhiramat@...nel.org, oleg@...hat.com
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        anup@...infault.org, linux-csky@...r.kernel.org,
        greentime.hu@...ive.com, zong.li@...ive.com, guoren@...nel.org,
        me@...ki.ch, bjorn.topel@...il.com,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH v3 3/7] riscv: Fixup kprobes handler couldn't change pc

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

The "Changing Execution Path" section in the Documentation/kprobes.txt
said:

Since kprobes can probe into a running kernel code, it can change the
register set, including instruction pointer.

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Palmer Dabbelt <palmerdabbelt@...gle.com>
---
 arch/riscv/kernel/mcount-dyn.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index 35a6ed7..4b58b54 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -123,6 +123,7 @@ ENDPROC(ftrace_caller)
 	sd	ra, (PT_SIZE_ON_STACK+8)(sp)
 	addi	s0, sp, (PT_SIZE_ON_STACK+16)
 
+	sd ra,  PT_EPC(sp)
 	sd x1,  PT_RA(sp)
 	sd x2,  PT_SP(sp)
 	sd x3,  PT_GP(sp)
@@ -157,6 +158,7 @@ ENDPROC(ftrace_caller)
 	.endm
 
 	.macro RESTORE_ALL
+	ld ra,  PT_EPC(sp)
 	ld x1,  PT_RA(sp)
 	ld x2,  PT_SP(sp)
 	ld x3,  PT_GP(sp)
@@ -190,7 +192,6 @@ ENDPROC(ftrace_caller)
 	ld x31, PT_T6(sp)
 
 	ld	s0, (PT_SIZE_ON_STACK)(sp)
-	ld	ra, (PT_SIZE_ON_STACK+8)(sp)
 	addi	sp, sp, (PT_SIZE_ON_STACK+16)
 	.endm
 
-- 
2.7.4