[PATCH v2 08/11] uprobes: Change handle_trampoline() to flush the frames invalidated by longjmp()

[Oleg Nesterov]

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return, so when func_1() returns the kernel uses the no longer valid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.

Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
 kernel/events/uprobes.c |   29 ++++++++++++++++++-----------
 1 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c5f316e..93d939c 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;
-- 
1.5.5.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/