Messages in this thread Patch in this message | | | Date | Fri, 6 Apr 2012 00:22:03 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 5/6] uprobes: teach handle_swbp() to rely on "is_swbp" rather than uprobes_srcu |
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Currently handle_swbp() assumes that it can't race with unregister, so it roughly does:
if (find_uprobe(vaddr)) process_uprobe(); else send_sig(SIGTRAP);
This relies on the not-really-working uprobes_srcu code we are going to remove.
With this patch we rely on the result of is_swbp_at_addr_fast(bp_vaddr) if find_uprobe() fails.
If is_swbp == 1, then we hit the normal int3, we should send SIGTRAP.
If is_swbp == 0, we raced with uprobe_unregister(), we simply restart this insn again.
The "difficult" case is is_swbp == -EFAULT, when we can't read this memory. In this case I think we should restart too, and this is more correct compared to the current code which sends SIGTRAP.
Ignoring ENOMEM/etc from get_user_pages(), this can only happen if another thread unmaps this memory before find_active_uprobe() takes mmap_sem. It would be better to pretend it was unmapped before this insn was executed, restart, and get SIGSEGV. --- kernel/events/uprobes.c | 18 +++++++++++++++--- 1 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 2af458d..ed76ee5 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1538,14 +1538,26 @@ static void handle_swbp(struct pt_regs *regs) struct uprobe_task *utask; struct uprobe *uprobe; unsigned long bp_vaddr; - int is_swbp; + int uninitialized_var(is_swbp); bp_vaddr = uprobe_get_swbp_addr(regs); uprobe = find_active_uprobe(bp_vaddr, &is_swbp); if (!uprobe) { - /* No matching uprobe; signal SIGTRAP. */ - send_sig(SIGTRAP, current, 0); + if (is_swbp > 0) { + /* No matching uprobe; signal SIGTRAP. */ + send_sig(SIGTRAP, current, 0); + } else { + /* + * Either we raced with uprobe_unregister() or we can't + * access this memory. The latter is only possible if + * another thread plays with our ->mm. In both cases + * we can simply restart. If this vma was unmapped we + * can pretend this insn was not executed yet and get + * the (correct) SIGSEGV after restart. + */ + instruction_pointer_set(regs, bp_vaddr); + } return; } -- 1.5.5.1
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