[PATCH] kprobes/powerpc: Fix possible system crash during out-of-line single-stepping

[Will Schmidt]

On Fri, 2006-11-08 at 17:01 +0530, Ananth N Mavinakayanahalli wrote:
> - On archs that have no-exec support, we vmalloc() a executable scratch
> area of PAGE_SIZE and divide it up into an array of slots of maximum
> instruction size for that arch
> - On a kprobe registration, the original instruction is copied to the
> first available free slot, so if multiple kprobes are registered, chances
> are, they get contiguous slots
> - On POWER4, due to not having coherent icaches, we could hit a situation
> where a probe that is registered on one processor, is hit immediately on
> another. This second processor could have fetched the stream of text from
> the out-of-line single-stepping area *before* the probe registration
> completed, possibly due to an earlier (and a different) kprobe hit and
> hence would see stale data at the slot.
> 
> Executing such an arbitrary instruction lead to a problem as reported
> in LTC bugzilla 23555.
> 
> The correct solution is to call flush_icache_range() as soon as the
> instruction is copied for out-of-line single-stepping, so the correct
> instruction is seen on all processors.
> 
> Thanks to Will Schmidt who tracked this down.
> 
> Ananth
> ---
> 
> Signed-off-by: Ananth N Mavinakayanahalli <ananth at in.ibm.com>

Acked-by: Will Schmidt <will_schmidt at vnet.ibm.com>

-Will