From: nfortino@nvidia•com (Nickolas Fortino)
To: linux-arm-kernel@lists•infradead.org
Subject: preempted dup_mm misses TLB invalidate
Date: Mon, 15 Jul 2013 11:19:23 -0700 [thread overview]
Message-ID: <51E43D2B.9090709@nvidia.com> (raw)
I?ve noticed an issue in simulation where the Linux kernel is executing
a user process when the page tables and TLBs have gotten out of sync.
The page tables have a page marked as user read only, but the TLB has
the page marked as user read/write.
I?ve traced the issue back to the handling of copy on write pages
generated from the ?do_fork?, ?copy_process?, ?dup_mm?, ?dup_mmap? call
stack. If run without interruption, ?dup_mmap? calls
?flush_tlb_mm(oldmm)? on completion, avoiding any issues. In this case,
however, about 4 million instructions after ?dup_mm? is called,
?copy_pte_range? yields to another thread via __cond_resched. About 20
million instructions later, a user process with the ASID of the source
mm is scheduled. This process performs a store to a page modified from
read/write to read only in the copy on write logic of ?copy_one_pte?.
Because the TLB was not invalidated, the store hits on a TLB entry with
read/write permissions and succeeds without a fault.
What invariant in the Linux kernel is supposed to prevent this from
happening? Note I have not observed user visible corruption, but it
seems very unlikely a successful store to a page marked as read only in
the kernel is safe.
For reference, this issue was found with the Linux 3.7 kernel coming
from the Linaro 12.12 release available at
http://releases.linaro.org/12.12/android/vexpress
next reply other threads:[~2013-07-15 18:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-15 18:19 Nickolas Fortino [this message]
2013-07-17 19:27 ` preempted dup_mm misses TLB invalidate Catalin Marinas
2013-07-17 19:52 ` Stephen Warren
2013-07-17 20:01 ` Russell King - ARM Linux
2013-07-17 20:11 ` Stephen Warren
2013-07-17 20:09 ` Nickolas Fortino
2013-07-17 20:34 ` Russell King - ARM Linux
2013-07-17 21:03 ` Nickolas Fortino
2013-07-17 21:21 ` Russell King - ARM Linux
2013-07-18 1:48 ` Nickolas Fortino
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