linux-kernel - [PATCH] riscv: kprobes: Fix incorrect address calculation

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Message-Id: <20241119111056.2554419-1-namcao@linutronix.de>
Date: Tue, 19 Nov 2024 12:10:56 +0100
From: Nam Cao <namcao@...utronix.de>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Samuel Holland <samuel.holland@...ive.com>,
	Björn Töpel <bjorn@...osinc.com>,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: John Ogness <john.ogness@...utronix.de>,
	Nam Cao <namcao@...utronix.de>,
	stable@...r.kernel.org
Subject: [PATCH] riscv: kprobes: Fix incorrect address calculation

p->ainsn.api.insn is a pointer to u32, therefore arithmetic operations are
multiplied by four. This is clearly undesirable for this case.

Cast it to (void *) first before any calculation.

Below is a sample before/after. The dumped memory is two kprobe slots, the
first slot has

  - c.addiw a0, 0x1c (0x7125)
  - ebreak           (0x00100073)

and the second slot has:

  - c.addiw a0, -4   (0x7135)
  - ebreak           (0x00100073)

Before this patch:

(gdb) x/16xh 0xff20000000135000
0xff20000000135000:	0x7125	0x0000	0x0000	0x0000	0x7135	0x0010	0x0000	0x0000
0xff20000000135010:	0x0073	0x0010	0x0000	0x0000	0x0000	0x0000	0x0000	0x0000

After this patch:

(gdb) x/16xh 0xff20000000125000
0xff20000000125000:	0x7125	0x0073	0x0010	0x0000	0x7135	0x0073	0x0010	0x0000
0xff20000000125010:	0x0000	0x0000	0x0000	0x0000	0x0000	0x0000	0x0000	0x0000

Fixes: b1756750a397 ("riscv: kprobes: Use patch_text_nosync() for insn slots")
Signed-off-by: Nam Cao <namcao@...utronix.de>
Cc: stable@...r.kernel.org
---
 arch/riscv/kernel/probes/kprobes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index 474a65213657..d2dacea1aedd 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -30,7 +30,7 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 	p->ainsn.api.restore = (unsigned long)p->addr + len;
 
 	patch_text_nosync(p->ainsn.api.insn, &p->opcode, len);
-	patch_text_nosync(p->ainsn.api.insn + len, &insn, GET_INSN_LENGTH(insn));
+	patch_text_nosync((void *)p->ainsn.api.insn + len, &insn, GET_INSN_LENGTH(insn));
 }
 
 static void __kprobes arch_prepare_simulate(struct kprobe *p)
-- 
2.39.5