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

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Message-ID: <20150828053037.GB26741@gmail.com>
Date:	Fri, 28 Aug 2015 07:30:37 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
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


* 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.

Thanks,

	Ingo
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