lkml.org 
[lkml]   [2012]   [Apr]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH 5/6] uprobes: teach handle_swbp() to rely on "is_swbp" rather than uprobes_srcu
    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



    \
     
     \ /
      Last update: 2012-04-06 00:25    [W:0.021 / U:60.156 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site