riscv: kprobe: Fixup kernel panic when probing an illegal position

From: Guo Ren <[email protected]>

The kernel would panic when probed for an illegal position. eg:

(CONFIG_RISCV_ISA_C=n)

echo 'p:hello kernel_clone+0x16 a0=%a0' >> kprobe_events echo 1 > events/kprobes/hello/enable
cat trace

Kernel panic - not syncing: stack-protector: Kernel stack
is corrupted in: __do_sys_newfstatat+0xb8/0xb8
CPU: 0 PID: 111 Comm: sh Not tainted
6.2.0-rc1-00027-g2d398fe49a4d #490
Hardware name: riscv-virtio,qemu (DT)
Call Trace:
[<ffffffff80007268>] dump_backtrace+0x38/0x48
[<ffffffff80c5e83c>] show_stack+0x50/0x68
[<ffffffff80c6da28>] dump_stack_lvl+0x60/0x84
[<ffffffff80c6da6c>] dump_stack+0x20/0x30
[<ffffffff80c5ecf4>] panic+0x160/0x374
[<ffffffff80c6db94>] generic_handle_arch_irq+0x0/0xa8
[<ffffffff802deeb0>] sys_newstat+0x0/0x30
[<ffffffff800158c0>] sys_clone+0x20/0x30
[<ffffffff800039e8>] ret_from_syscall+0x0/0x4
---[ end Kernel panic - not syncing: stack-protector:
Kernel stack is corrupted in: __do_sys_newfstatat+0xb8/0xb8 ]---

That is because the kprobe's ebreak instruction broke the kernel's original code. The user should guarantee the correction of the probe position, but it couldn't make the kernel panic.

This patch adds arch_check_kprobe in arch_prepare_kprobe to prevent an illegal position (Such as the middle of an instruction).

---
Changelog
V2:
- Fixup misaligned load (Thx Bjorn)

---
 arch/riscv/kernel/probes/kprobes.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

index f21592d20306..41c7481afde3 100644
@@ -48,6 +48,21 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
 	post_kprobe_handler(p, kcb, regs);
 }
 
+static bool __kprobes arch_check_kprobe(struct kprobe *p)
+{
+	unsigned long tmp  = (unsigned long)p->addr - p->offset;
+	unsigned long addr = (unsigned long)p->addr;
+
+	while (tmp <= addr) {
+		if (tmp == addr)
+			return true;
+
+		tmp += GET_INSN_LENGTH(*(u16 *)tmp);
+	}
+
+	return false;
+}
+
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	unsigned long probe_addr = (unsigned long)p->addr;

@@ -55,6 +70,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	if (probe_addr & 0x1)
 		return -EILSEQ;
 
+	if (!arch_check_kprobe(p))
+		return -EILSEQ;
+
 	/* copy instruction */
 	p->opcode = *p->addr;
 

2.36.1