[POWERPC] kprobes: Fix possible system crash during out-of-line single-stepping
- 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. Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com> Acked-by: Will Schmidt <will_schmidt@vnet.ibm.com> Signed-off-by: Paul Mackerras <paulus@samba.org>
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@ -61,6 +61,8 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
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if (!ret) {
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memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
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p->opcode = *p->addr;
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flush_icache_range((unsigned long)p->ainsn.insn,
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(unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
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}
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return ret;
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