riscv: kprobes: Fix incorrect address calculation

commit 13134cc949 upstream.

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: b1756750a3 ("riscv: kprobes: Use patch_text_nosync() for insn slots")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Cc: stable@vger.kernel.org
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20241119111056.2554419-1-namcao@linutronix.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
[rebase to v6.6]
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/riscv/kernel/probes/kprobes.c

@@ -29,7 +29,7 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 	p->ainsn.api.restore = (unsigned long)p->addr + offset;
 
 	patch_text_nosync(p->ainsn.api.insn, &p->opcode, 1);
-	patch_text_nosync(p->ainsn.api.insn + offset, &insn, 1);
+	patch_text_nosync((void *)p->ainsn.api.insn + offset, &insn, 1);
 }
 
 static void __kprobes arch_prepare_simulate(struct kprobe *p)