linux-kernel - Re: [PATCH 3/3] kallsyms: Unexport kallsyms_lookup_name() and kallsyms_on_each

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Message-ID: <20200221151109.gxrhyaybjwxqktul@ast-mbp>
Date:   Fri, 21 Feb 2020 07:11:10 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        akpm@...ux-foundation.org,
        "K . Prasad" <prasad@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Quentin Perret <qperret@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 3/3] kallsyms: Unexport kallsyms_lookup_name() and
 kallsyms_on_each_symbol()

On Fri, Feb 21, 2020 at 11:44:04AM +0000, Will Deacon wrote:
> kallsyms_lookup_name() and kallsyms_on_each_symbol() are exported to
> modules despite having no in-tree users and being wide open to abuse by
> out-of-tree modules that can use them as a method to invoke arbitrary
> non-exported kernel functions.
> 
> Unexport kallsyms_lookup_name() and kallsyms_on_each_symbol().
> 
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Quentin Perret <qperret@...gle.com>
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  kernel/kallsyms.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index a9b3f660dee7..16c8c605f4b0 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -175,7 +175,6 @@ unsigned long kallsyms_lookup_name(const char *name)
>  	}
>  	return module_kallsyms_lookup_name(name);
>  }
> -EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
>  
>  int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
>  				      unsigned long),
> @@ -194,7 +193,6 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
>  	}
>  	return module_kallsyms_on_each_symbol(fn, data);
>  }
> -EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);

Looking at commit 75a66614db21 ("Ksplice: Add functions for walking kallsyms symbols")
this change will break ksplice.
But I think it's the right call. live-patching needs to find a way to be better
integrated with the core kernel.

Acked-by: Alexei Starovoitov <ast@...nel.org>