linux-kernel - Re: [PATCH 1/2] perf/x86/intel/ds: Work around BTS leaking kernel addresses

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Date:	Fri, 28 Aug 2015 09:06:32 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH 1/2] perf/x86/intel/ds: Work around BTS leaking kernel addresses

Ingo Molnar <mingo@...nel.org> writes:

> * Alexander Shishkin <alexander.shishkin@...ux.intel.com> wrote:
>
>> +	for (at = base; at < top; at++) {
>> +		/*
>> +		 * Note that right now *this* BTS code only works if
>> +		 * attr::exclude_kernel is set, but let's keep this extra
>> +		 * check here in case that changes.
>> +		 */
>> +		if (event->attr.exclude_kernel &&
>> +		    (at->from >= PAGE_OFFSET || at->to >= PAGE_OFFSET))
>> +			skip++;
>
> Yeah, so that only works on 32-bit kernels, on 64-bit kernels the check for kernel 
> addresses is to see whether it's a negative address. PAGE_OFFSET points to above 
> any hypervisor's address, so even with your fix we could still leak hypervisor 
> addresses.
>
> I.e. use the kernel_ip() primitive instead.

That's what I've been looking for, thanks!

Regards,
--
Alex
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