[PATCH V2] riscv: kprobe: Fixup kernel panic when probing an illegal position

[guoren at kernel.org]

From: Guo Ren <guoren at linux.alibaba.com>

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).

Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
Signed-off-by: Guo Ren <guoren at kernel.org>
---
Changelog
V2:
 - Fixup misaligned load (Thx Bjorn)
---
 arch/riscv/kernel/probes/kprobes.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
index f21592d20306..41c7481afde3 100644
--- a/arch/riscv/kernel/probes/kprobes.c
+++ b/arch/riscv/kernel/probes/kprobes.c
@@ -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