Commit-ID: 5eeb50de42fd3251845d03c556db012267c72b3f
Gitweb: http://git.kernel.org/tip/5eeb50de42fd3251845d03c556db012267c72b3f
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Tue, 21 Jul 2015 15:40:21 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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kernel uses the no longer valid return_instance of func_2().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@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Acked-by: Anton Arapov <arapov@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20150721134021.GA4773@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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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