linux-kernel - Re: [PATCH 1/3 v8] livepatch: add old_sympos as disambiguator field to klp

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Date:	Mon, 23 Nov 2015 10:47:34 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Chris J Arges <chris.j.arges@...onical.com>
cc:	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	jpoimboe@...hat.com, jikos@...nel.org, pmladek@...e.com,
	jeyu@...hat.com, Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.com>
Subject: Re: [PATCH 1/3 v8] livepatch: add old_sympos as disambiguator field
 to klp_func

On Fri, 20 Nov 2015, Chris J Arges wrote:

> Currently, patching objects with duplicate symbol names fail because the
> creation of the sysfs function directory collides with the previous
> attempt. Appending old_addr to the function name is problematic as it
> reveals the address of the function being patch to a normal user. Using
> the symbol's occurrence in kallsyms to postfix the function name in the
> sysfs directory solves the issue of having consistent unique names and
> ensuring that the address is not exposed to a normal user.
> 
> In addition, using the symbol position as the user's method to disambiguate
> symbols instead of addr allows for disambiguating symbols in modules as
> well for both function addresses and for relocs. This also simplifies much
> of the code. Special handling for kASLR is no longer needed and can be
> removed. The klp_find_verify_func_addr function can be replaced by
> klp_find_object_symbol, and klp_verify_vmlinux_symbol and its callback can
> be removed completely.
> 
> In cases of duplicate symbols, old_sympos will be used to disambiguate
> instead of old_addr. By default old_sympos will be 0, and patching will
> only succeed if the symbol is unique. Specifying a positive value will
> ensure that occurrence of the symbol in kallsyms for the patched object
> will be used for patching if it is valid.
> 
> In addition, make old_addr an internal structure field not to be specified
> by the user. Finally, remove klp_find_verify_func_addr as it can be
> replaced by klp_find_object_symbol directly.
> 
> Support for symbol position disambiguation for relocations is added in the
> next patch in this series.
> 
> Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>

Reviewed-by: Miroslav Benes <mbenes@...e.cz>

Miroslav
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