lkml.org 
[lkml]   [2013]   [Apr]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] Fix perf LBR filtering
On Wed, Apr 24, 2013 at 04:04:53PM -0700, Andi Kleen wrote:
> Possible options:
>
> I) Disable FAR calls for ANY_CALL/RETURNS.
> This just means syscalls are not logged
> as calls. This also lowers the overhead of call logging.
> This changes semantics slightly.
> This is reasonable on Sandy Bridge and later, but would
> cause additional problems on Nehalem and Westmere with
> their additional filters.
>
> II) Simple disable any filtering for kernel space.
> This means interrupts in kernel space are reported as calls
> and on Nehalem/Westmere some indirect jumps are reported
> as calls too
>
> III) Enumerate all the kernel entry points and check.
> Any bad call must have a kernel entry point as to.
> This seemed to fragile to maintain.
>
> IV) Enumerate all kernel code and check for these ranges.
> Quite complicated, especially with the new kernel code JITs.
> Would also allow to probe for kernel code (defeating randomized kernel)

So why not do the same as we do for userspace? Copy MAX_INSN_SIZE bytes
and trap -EFAULT.

With Steven's recent NMI nesting stuff we should be able to take the fault and
do the fixup_exception() thing. Or alternatively we could software walk the
kernel pagetables.



\
 
 \ /
  Last update: 2013-04-25 19:01    [W:0.098 / U:1.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site