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[PATCH 2/3] perf/x86: Tighten up the kernel_ip() check

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  [PATCH 2/3] perf/x86: Tighten up the kernel_ip() check Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-15 15:40 +0200
    Re: [PATCH 2/3] perf/x86: Tighten up the kernel_ip() check Peter Zijlstra <peterz@infradead.org> - 2016-09-15 16:10 +0200

#1484174 — [PATCH 2/3] perf/x86: Tighten up the kernel_ip() check

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@vger.kernel.org # 4.7
Reported-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.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
 }
 
-- 
2.9.3

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#1484208

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@vger.kernel.org # 4.7
> Reported-by: Adrian Hunter <adrian.hunter@intel.com>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.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.

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