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From: Ingo Molnar <mingo@kernel.org>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org,
	Arnaldo Carvalho de Melo <acme@infradead.org>
Subject: Re: [PATCH 1/2] perf/x86/intel/ds: Work around BTS leaking kernel addresses
Date: Fri, 28 Aug 2015 07:30:37 +0200	[thread overview]
Message-ID: <20150828053037.GB26741@gmail.com> (raw)
In-Reply-To: <1440688422-27954-2-git-send-email-alexander.shishkin@linux.intel.com>


* Alexander Shishkin <alexander.shishkin@linux.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

  reply	other threads:[~2015-08-28  5:30 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-27 15:13 [PATCH 0/2] perf/x86/intel: Work around BTS leaking kernel addresses Alexander Shishkin
2015-08-27 15:13 ` [PATCH 1/2] perf/x86/intel/ds: " Alexander Shishkin
2015-08-28  5:30   ` Ingo Molnar [this message]
2015-08-28  6:06     ` Alexander Shishkin
2015-08-27 15:13 ` [PATCH 2/2] perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems Alexander Shishkin
2015-08-28  5:31   ` Ingo Molnar
2015-08-28  9:40     ` Alexander Shishkin

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