From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755649AbaDMRq2 (ORCPT ); Sun, 13 Apr 2014 13:46:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:4643 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755089AbaDMRp7 (ORCPT ); Sun, 13 Apr 2014 13:45:59 -0400 Date: Sun, 13 Apr 2014 19:45:53 +0200 From: Oleg Nesterov To: Ingo Molnar , Srikar Dronamraju Cc: Ananth N Mavinakayanahalli , Anton Arapov , David Long , Denys Vlasenko , "Frank Ch. Eigler" , Jim Keniston , Jonathan Lebon , Masami Hiramatsu , linux-kernel@vger.kernel.org Subject: [PATCH v3 09/15] uprobes/x86: Teach arch_uprobe_post_xol() to restart if possible Message-ID: <20140413174553.GA11871@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140413174508.GA11811@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 files changed, 16 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index e0f1406..1ea7e1a 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; } } -- 1.5.5.1