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

[Björn Töpel]

guoren@xxxxxxxxxx writes:

> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> 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).

Nice!

@liaochang Will you remove your patch from the OPTPROBE series?

> Fixes: c22b0bcb1dd0 ("riscv: Add kprobes supported")
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> ---
>  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..475989f06d6d 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(*(kprobe_opcode_t *)tmp);

kprobe_opcode_t is u32; This can trigger a misaligned load, right?

> +	}
> +
> +	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;

Not related to your patch, but this can also trigger a misaligned load.


Björn