Messages in this thread Patch in this message | | | Date | Thu, 3 Apr 2014 22:01:55 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 9/7] uprobes/x86: Teach arch_uprobe_post_xol() to restart if possible |
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SIGILL after the failed arch_uprobe_post_xol() should only be used as a last resort, we should try to restart the probed insn if possible.
Currently only adjust_ret_addr() can fail, and this can only happen if another thread unmapped our stack after we executed "call" out-of-line. Most probably the application if buggy, but even in this case it can have a handler for SIGSEGV/etc. And in theory it can be even correct and do something non-trivial with its memory.
Of course we can't restart unconditionally, so arch_uprobe_post_xol() does this only if ->post_xol() returns -ERESTART even if currently this is the only possible error.
Note: this is not "perfect" because handler_chain() we actually do not want the extra handler_chain() after restart, but I think this is the best solution we can realistically do without too much uglifications.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- arch/x86/kernel/uprobes.c | 15 +++++++++++---- 1 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 3bdfb6e..78c4bb3 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -443,16 +443,17 @@ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs { struct uprobe_task *utask = current->utask; long correction = (long)(utask->vaddr - utask->xol_vaddr); - int ret = 0; handle_riprel_post_xol(auprobe, regs, &correction); if (auprobe->fixups & UPROBE_FIX_IP) regs->ip += correction; - if (auprobe->fixups & UPROBE_FIX_CALL) - ret = adjust_ret_addr(regs->sp, correction); + if (auprobe->fixups & UPROBE_FIX_CALL) { + if (adjust_ret_addr(regs->sp, correction)) + return -ERESTART; + } - return ret; + return 0; } static struct uprobe_xol_ops default_xol_ops = { @@ -599,6 +600,12 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) int err = auprobe->ops->post_xol(auprobe, regs); if (err) { arch_uprobe_abort_xol(auprobe, regs); + /* + * Restart the probed insn. ->post_xol() must ensure + * this is really possible if it returns -ERESTART. + */ + if (err == -ERESTART) + return 0; return err; } } -- 1.5.5.1
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