[tip:perf/core] uprobes/x86: Reimplement arch_uretprobe_is_alive( )

[tip-bot for Oleg Nesterov <tipbot@zytor.com>]

Commit-ID:  7b868e4802a86d867aad1be0471b5767d9c20e10
Gitweb:     http://git.kernel.org/tip/7b868e4802a86d867aad1be0471b5767d9c20e10
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Tue, 21 Jul 2015 15:40:18 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 31 Jul 2015 10:38:05 +0200

uprobes/x86: Reimplement arch_uretprobe_is_alive()

Add the x86 specific version of arch_uretprobe_is_alive()
helper. It returns true if the stack frame mangled by
prepare_uretprobe() is still on stack. So if it returns false,
we know that the probed function has already returned.

We add the new return_instance->stack member and change the
generic code to initialize it in prepare_uretprobe, but it
should be equally useful for other architectures.

TODO: this assumes that the probed application can't use
      multiple stacks (say sigaltstack). We will try to improve
      this logic later.

Tested-by: Pratyush Anand <panand@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Anton Arapov <arapov@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150721134018.GA4766@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/uprobes.c | 5 +++++
 include/linux/uprobes.h   | 1 +
 kernel/events/uprobes.c   | 1 +
 3 files changed, 7 insertions(+)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 6647624..58e9b84 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -985,3 +985,8 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs
 
 	return -1;
 }
+
+bool arch_uretprobe_is_alive(struct return_instance *ret, struct pt_regs *regs)
+{
+	return regs->sp <= ret->stack;
+}
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 50d2764..7ab6d2c 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -95,6 +95,7 @@ struct uprobe_task {
 struct return_instance {
 	struct uprobe		*uprobe;
 	unsigned long		func;
+	unsigned long		stack;		/* stack pointer */
 	unsigned long		orig_ret_vaddr; /* original return address */
 	bool			chained;	/* true, if instance is nested */
 
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 1c71b62..c5f316e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1562,6 +1562,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
 
 	ri->uprobe = get_uprobe(uprobe);
 	ri->func = instruction_pointer(regs);
+	ri->stack = user_stack_pointer(regs);
 	ri->orig_ret_vaddr = orig_ret_vaddr;
 	ri->chained = chained;