riscv/kprobe: Fix instruction simulation of JALR

Set kprobe at 'jalr 1140(ra)' of vfs_write results in the following
crash:

[   32.092235] Unable to handle kernel access to user memory without uaccess routines at virtual address 00aaaaaad77b1170
[   32.093115] Oops [#1]
[   32.093251] Modules linked in:
[   32.093626] CPU: 0 PID: 135 Comm: ftracetest Not tainted 6.2.0-rc2-00013-gb0aa5e5df0cb-dirty #16
[   32.093985] Hardware name: riscv-virtio,qemu (DT)
[   32.094280] epc : ksys_read+0x88/0xd6
[   32.094855]  ra : ksys_read+0xc0/0xd6
[   32.095016] epc : ffffffff801cda80 ra : ffffffff801cdab8 sp : ff20000000d7bdc0
[   32.095227]  gp : ffffffff80f14000 tp : ff60000080f9cb40 t0 : ffffffff80f13e80
[   32.095500]  t1 : ffffffff8000c29c t2 : ffffffff800dbc54 s0 : ff20000000d7be60
[   32.095716]  s1 : 0000000000000000 a0 : ffffffff805a64ae a1 : ffffffff80a83708
[   32.095921]  a2 : ffffffff80f160a0 a3 : 0000000000000000 a4 : f229b0afdb165300
[   32.096171]  a5 : f229b0afdb165300 a6 : ffffffff80eeebd0 a7 : 00000000000003ff
[   32.096411]  s2 : ff6000007ff76800 s3 : fffffffffffffff7 s4 : 00aaaaaad77b1170
[   32.096638]  s5 : ffffffff80f160a0 s6 : ff6000007ff76800 s7 : 0000000000000030
[   32.096865]  s8 : 00ffffffc3d97be0 s9 : 0000000000000007 s10: 00aaaaaad77c9410
[   32.097092]  s11: 0000000000000000 t3 : ffffffff80f13e48 t4 : ffffffff8000c29c
[   32.097317]  t5 : ffffffff8000c29c t6 : ffffffff800dbc54
[   32.097505] status: 0000000200000120 badaddr: 00aaaaaad77b1170 cause: 000000000000000d
[   32.098011] [<ffffffff801cdb72>] ksys_write+0x6c/0xd6
[   32.098222] [<ffffffff801cdc06>] sys_write+0x2a/0x38
[   32.098405] [<ffffffff80003c76>] ret_from_syscall+0x0/0x2

Since the rs1 and rd might be the same one, such as 'jalr 1140(ra)',
hence it requires obtaining the target address from rs1 followed by
updating rd.

Fixes: c22b0bcb ("riscv: Add kprobes supported")
Signed-off-by: Liao Chang <liaochang1@huawei.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20230116064342.2092136-1-liaochang1@huawei.com
[Palmer: Pick Guo's cleanup]
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/probes/simulate-insn.c

@@ -71,11 +71,11 @@ bool __kprobes simulate_jalr(u32 opcode, unsigned long addr, struct pt_regs *reg
 	u32 rd_index = (opcode >> 7) & 0x1f;
 	u32 rs1_index = (opcode >> 15) & 0x1f;
 
-	ret = rv_insn_reg_set_val(regs, rd_index, addr + 4);
+	ret = rv_insn_reg_get_val(regs, rs1_index, &base_addr);
 	if (!ret)
 		return ret;
 
-	ret = rv_insn_reg_get_val(regs, rs1_index, &base_addr);
+	ret = rv_insn_reg_set_val(regs, rd_index, addr + 4);
 	if (!ret)
 		return ret;