riscv/kprobe: Fix instruction simulation of JALR

In the Linux kernel, the following vulnerability has been resolved:

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.

[Palmer: Pick Guo's cleanup]