linux-kernel - [PATCH] riscv, kprobes: Stricter c.jr/c.jalr decoding

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Message-Id: <20230102160748.1307289-1-bjorn@kernel.org>
Date:   Mon,  2 Jan 2023 17:07:48 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...nel.org>
Cc:     Björn Töpel <bjorn@...osinc.com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: [PATCH] riscv, kprobes: Stricter c.jr/c.jalr decoding

From: Björn Töpel <bjorn@...osinc.com>

In the compressed instruction extension, c.jr, c.jalr, c.mv, and c.add
is encoded the following way (each instruction is 16b):

---+-+-----------+-----------+--
100 0 rs1[4:0]!=0       00000 10 : c.jr
100 1 rs1[4:0]!=0       00000 10 : c.jalr
100 0  rd[4:0]!=0 rs2[4:0]!=0 10 : c.mv
100 1  rd[4:0]!=0 rs2[4:0]!=0 10 : c.add

The following logic is used to decode c.jr and c.jalr:

  insn & 0xf007 == 0x8002 => instruction is an c.jr
  insn & 0xf007 == 0x9002 => instruction is an c.jalr

When 0xf007 is used to mask the instruction, c.mv can be incorrectly
decoded as c.jr, and c.add as c.jalr.

Correct the decoding by changing the mask from 0xf007 to 0xf07f.

Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
Signed-off-by: Björn Töpel <bjorn@...osinc.com>
---
 arch/riscv/kernel/probes/simulate-insn.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
index cb6ff7dccb92..de8474146a9b 100644
--- a/arch/riscv/kernel/probes/simulate-insn.h
+++ b/arch/riscv/kernel/probes/simulate-insn.h
@@ -31,9 +31,9 @@ __RISCV_INSN_FUNCS(fence,	0x7f, 0x0f);
 	} while (0)
 
 __RISCV_INSN_FUNCS(c_j,		0xe003, 0xa001);
-__RISCV_INSN_FUNCS(c_jr,	0xf007, 0x8002);
+__RISCV_INSN_FUNCS(c_jr,	0xf07f, 0x8002);
 __RISCV_INSN_FUNCS(c_jal,	0xe003, 0x2001);
-__RISCV_INSN_FUNCS(c_jalr,	0xf007, 0x9002);
+__RISCV_INSN_FUNCS(c_jalr,	0xf07f, 0x9002);
 __RISCV_INSN_FUNCS(c_beqz,	0xe003, 0xc001);
 __RISCV_INSN_FUNCS(c_bnez,	0xe003, 0xe001);
 __RISCV_INSN_FUNCS(c_ebreak,	0xffff, 0x9002);

base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2
-- 
2.37.2