linux-kernel - Re: [PATCH v2] livepatch: x86: bugfix about kASLR

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Date:	Tue, 10 Nov 2015 08:07:21 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Zhou Chengming <zhouchengming1@...wei.com>
Cc:	sjenning@...hat.com, jkosina@...e.cz, vojtech@...e.cz,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	guohanjun@...wei.com, huawei.libin@...wei.com, xiexiuqi@...wei.com,
	cbay@...aysdata.com
Subject: Re: [PATCH v2] livepatch: x86: bugfix about kASLR

On Fri, Nov 06, 2015 at 02:25:00PM +0800, Zhou Chengming wrote:
> When enable KASLR, livepatch will adjust old_addr of changed
> function accordingly. So do the same thing for reloc.
> 
> [PATCH v1] https://lkml.org/lkml/2015/11/4/91
> 
> Reported-by: Cyril B. <cbay@...aysdata.com>
> Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com>
> ---
>  kernel/livepatch/core.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 6e53441..db545cb 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -294,6 +294,12 @@ static int klp_write_object_relocations(struct module *pmod,
>  
>  	for (reloc = obj->relocs; reloc->name; reloc++) {
>  		if (!klp_is_module(obj)) {
> +
> +#if defined(CONFIG_RANDOMIZE_BASE)
> +			/* If KASLR has been enabled, adjust old value accordingly */
> +			if (kaslr_enabled())
> +				reloc->val += kaslr_offset();
> +#endif
>  			ret = klp_verify_vmlinux_symbol(reloc->name,
>  							reloc->val);
>  			if (ret)

Zhou, thanks a lot for this fix.

Generally I think this patch is fine.  However, Chris J Arges is working
on another patch[*] which may get rid of reloc->val as an input and make
this patch obsolete.

So, assuming Chris's patch eventually gets accepted, I don't see a need
for this one unless anybody wants it as a bug fix for 4.4.

[*] https://lkml.kernel.org/r/1447085770-11729-1-git-send-email-chris.j.arges@canonical.com

-- 
Josh
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