linux-kernel - Re: [PATCH v2 2/4] arm64: unwind: Prohibit probing on return

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Message-ID: <038c4b88-e7ef-aaab-0a79-5d7371719aa5@arm.com>
Date:   Tue, 23 Jul 2019 17:04:21 +0100
From:   James Morse <james.morse@....com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Dan Rue <dan.rue@...aro.org>,
        Matt Hart <matthew.hart@...aro.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Daniel Diaz <daniel.diaz@...aro.org>
Subject: Re: [PATCH v2 2/4] arm64: unwind: Prohibit probing on
 return_address()

Hi,

On 22/07/2019 08:48, Masami Hiramatsu wrote:
> Prohibit probing on return_address() and subroutines which
> is called from return_address(), since the it is invoked from
> trace_hardirqs_off() which is also kprobe blacklisted.

(Nits: "which are called" and "since it is")


> diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c
> index b21cba90f82d..7f8a143268b0 100644
> --- a/arch/arm64/kernel/return_address.c
> +++ b/arch/arm64/kernel/return_address.c
> @@ -8,6 +8,7 @@
>  
>  #include <linux/export.h>
>  #include <linux/ftrace.h>
> +#include <linux/kprobes.h>
>  
>  #include <asm/stack_pointer.h>
>  #include <asm/stacktrace.h>
> @@ -17,7 +18,7 @@ struct return_address_data {
>  	void *addr;
>  };
>  
> -static int save_return_addr(struct stackframe *frame, void *d)
> +static nokprobe_inline int save_return_addr(struct stackframe *frame, void *d)

This nokprobe_inline ends up as __always_inline if kprobes is enabled.
What do we expect the compiler to do with this? save_return_addr is passed as a
function-pointer to walk_stackframe()... I don't see how the compiler can inline it!

This would be needed for on_accessible_stack().
Should we cover ftrace_graph_get_ret_stack()?, or is that already in hand?


>  {
>  	struct return_address_data *data = d;
>  
> @@ -52,3 +53,4 @@ void *return_address(unsigned int level)
>  		return NULL;
>  }
>  EXPORT_SYMBOL_GPL(return_address);
> +NOKPROBE_SYMBOL(return_address);


Thanks,

James