linux-kernel - Re: [RFC PATCH 2/6] powerpc/trace: Add support for stack tracer

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Date:   Tue, 01 Jun 2021 19:21:27 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Torsten Duwe <duwe@...e.de>, Michael Ellerman <mpe@...erman.id.au>,
        Michal Suchanek <msuchanek@...e.de>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH 2/6] powerpc/trace: Add support for stack tracer

Naveen N. Rao wrote:
> +
> +unsigned long ftrace_get_traced_func_if_no_stackframe(unsigned long ip, unsigned long *stack)
> +{
> +	if (!is_ftrace_entry(ip))
> +		return 0;
> +
> +	if (IS_ENABLED(CONFIG_PPC32))
> +		return stack[11]; /* see MCOUNT_SAVE_FRAME */
> +
> +	if (!IS_ENABLED(CONFIG_MPROFILE_KERNEL))
> +		return 0;
> +
> +	return stack[(STACK_FRAME_OVERHEAD + offsetof(struct pt_regs, nip)) / sizeof(unsigned long)];

Looking at Daniel's patch to address KASAN errors with our stack walk 
code in show_stack() [*], I realized that I am not validating the stack 
pointer here for the above accesses...

[*] http://lkml.kernel.org/r/20210528074806.1311297-1-dja@axtens.net

> +}
> +
> +#ifdef CONFIG_STACK_TRACER
> +void stack_get_trace(unsigned long traced_ip,
> +		     unsigned long *stack_ref __maybe_unused,
> +		     unsigned long stack_size __maybe_unused,
> +		     int *tracer_frame)
> +{
> +	unsigned long sp, newsp, top, ip;
> +	int ftrace_call_found = 0;
> +	unsigned long *stack;
> +	int i = 0;
> +
> +	sp = current_stack_frame();
> +	top = (unsigned long)task_stack_page(current) + THREAD_SIZE;
> +
> +	while (validate_sp(sp, current, STACK_FRAME_OVERHEAD) && i < STACK_TRACE_ENTRIES) {
> +		stack = (unsigned long *) sp;
> +		newsp = stack[0];
> +		ip = stack[STACK_FRAME_LR_SAVE];
> +
> +		if (ftrace_call_found) {
> +			stack_dump_trace[i] = ip;
> +			stack_trace_index[i++] = top - sp;
> +		}

And I need to make the above accesses bypass KASAN as well.


- Naveen