From 75f9ef0b7f1aae33b7be7ba8d9c23c8cb48c2212 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 3 Apr 2014 20:52:19 +0200 Subject: [PATCH] uprobes/x86: Teach arch_uprobe_post_xol() to restart if possible 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. default_post_xol_op(UPROBE_FIX_CALL) can always restart, but as Jim pointed out it should not forget to pop off the return address pushed by this insn executed out-of-line. Note: this is not "perfect", we 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 Reviewed-by: Masami Hiramatsu Reviewed-by: Jim Keniston --- arch/x86/kernel/uprobes.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index e72903eacd43..cdd6909affcb 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -443,16 +443,22 @@ 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)) { + if (is_ia32_task()) + regs->sp += 4; + else + regs->sp += 8; + return -ERESTART; + } + } - return ret; + return 0; } static struct uprobe_xol_ops default_xol_ops = { @@ -599,6 +605,12 @@ 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; } } -- 2.30.2