Commit 75f9ef0b authored Apr 03, 2014 by Oleg Nesterov

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 <oleg@redhat.com>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>

parent 014940ba

arch/x86/kernel/uprobes.c

+16 −4

Original line number	Diff line number	Diff line
		@@ -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;
		}
		}