linux-kernel - Re: [PATCH 2/3] perf/x86: Tighten up the kernel

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Date:   Thu, 15 Sep 2016 16:07:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        vince@...ter.net, eranian@...gle.com,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 2/3] perf/x86: Tighten up the kernel_ip() check

On Thu, Sep 15, 2016 at 04:29:43PM +0300, Alexander Shishkin wrote:
> The kernel_ip() filter is used mostly by the DS/LBR code to look at the
> branch addresses, but Intel PT also uses it to validate the address
> filter offsets for kernel addresses, for which it is not sufficient:
> supplying something in bits 64:48 that's not a sign extension of the lower
> address bits (like 0xf00d000000000000) throws a #GP.
> 
> In the interest of improving everybody's kernel address checks, this
> patch adds address validation to kernel_ip().
> 
> Cc: stable@...r.kernel.org # 4.7
> Reported-by: Adrian Hunter <adrian.hunter@...el.com>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> ---
>  arch/x86/events/perf_event.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
> index 5874d8de1f..88fb389356 100644
> --- a/arch/x86/events/perf_event.h
> +++ b/arch/x86/events/perf_event.h
> @@ -783,7 +783,7 @@ static inline bool kernel_ip(unsigned long ip)
>  #ifdef CONFIG_X86_32
>  	return ip > PAGE_OFFSET;
>  #else
> -	return (long)ip < 0;
> +	return (long)ip < 0 && virt_addr_valid(ip);
>  #endif
>  }

I have a slight performance worry, this ends up being called a _lot_ on
older machines that have to do the PEBS LBR-fixup.