linux-kernel - [tip:perf/core] uprobes: Change handle_trampoline() to flush the frames invalidated by longjmp()

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Message-ID: <tip-5eeb50de42fd3251845d03c556db012267c72b3f@git.kernel.org>
Date:	Fri, 31 Jul 2015 07:00:09 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	srikar@...ux.vnet.ibm.com, luto@...capital.net,
	linux-kernel@...r.kernel.org, panand@...hat.com, hpa@...or.com,
	peterz@...radead.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, oleg@...hat.com, arapov@...il.com,
	mingo@...nel.org
Subject: [tip:perf/core] uprobes: Change handle_trampoline()
  to flush the frames invalidated by longjmp()

Commit-ID:  5eeb50de42fd3251845d03c556db012267c72b3f
Gitweb:     http://git.kernel.org/tip/5eeb50de42fd3251845d03c556db012267c72b3f
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 21 Jul 2015 15:40:21 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 31 Jul 2015 10:38:05 +0200

uprobes: Change handle_trampoline() to flush the frames invalidated by longjmp()

Test-case:

	#include <stdio.h>
	#include <setjmp.h>

	jmp_buf jmp;

	void func_2(void)
	{
		longjmp(jmp, 1);
	}

	void func_1(void)
	{
		if (setjmp(jmp))
			return;
		func_2();
		printf("ERR!! I am running on the caller's stack\n");
	}

	int main(void)
	{
		func_1();
		return 0;
	}

fails if you probe func_1() and func_2() because
handle_trampoline() assumes that the probed function should must
return and hit the bp installed be prepare_uretprobe(). But in
this case func_2() does not return, so when func_1() returns the
kernel uses the no longer valid return_instance of func_2().

Change handle_trampoline() to unwind ->return_instances until we
know that the next chain is alive or NULL, this ensures that the
current chain is the last we need to report and free.

Alternatively, every return_instance could use unique
trampoline_vaddr, in this case we could use it as a key. And
this could solve the problem with sigaltstack() automatically.

But this approach needs more changes, and it puts the "hard"
limit on MAX_URETPROBE_DEPTH. Plus it can not solve another
problem partially fixed by the next patch.

Note: this change has no effect on !x86, the arch-agnostic
version of arch_uretprobe_is_alive() just returns "true".

TODO: as documented by the previous change, arch_uretprobe_is_alive()
      can be fooled by sigaltstack/etc.

Tested-by: Pratyush Anand <panand@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Acked-by: Anton Arapov <arapov@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20150721134021.GA4773@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/uprobes.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c5f316e..93d939c8 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1774,6 +1774,7 @@ static void handle_trampoline(struct pt_regs *regs)
 {
 	struct uprobe_task *utask;
 	struct return_instance *ri, *next;
+	bool valid;
 
 	utask = current->utask;
 	if (!utask)
@@ -1783,18 +1784,24 @@ static void handle_trampoline(struct pt_regs *regs)
 	if (!ri)
 		goto sigill;
 
-	next = find_next_ret_chain(ri);
-	/*
-	 * TODO: we should throw out return_instance's invalidated by
-	 * longjmp(), currently we assume that the probed function always
-	 * returns.
-	 */
-	instruction_pointer_set(regs, ri->orig_ret_vaddr);
 	do {
-		handle_uretprobe_chain(ri, regs);
-		ri = free_ret_instance(ri);
-		utask->depth--;
-	} while (ri != next);
+		/*
+		 * We should throw out the frames invalidated by longjmp().
+		 * If this chain is valid, then the next one should be alive
+		 * or NULL; the latter case means that nobody but ri->func
+		 * could hit this trampoline on return. TODO: sigaltstack().
+		 */
+		next = find_next_ret_chain(ri);
+		valid = !next || arch_uretprobe_is_alive(next, regs);
+
+		instruction_pointer_set(regs, ri->orig_ret_vaddr);
+		do {
+			if (valid)
+				handle_uretprobe_chain(ri, regs);
+			ri = free_ret_instance(ri);
+			utask->depth--;
+		} while (ri != next);
+	} while (!valid);
 
 	utask->return_instances = ri;
 	return;
--
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