[0/3] kcov: fix unexpected faults

Message ID 20180504135535.53744-1-mark.rutland@arm.com
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  • kcov: fix unexpected faults
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Mark Rutland May 4, 2018, 1:55 p.m.

These patches fix a few issues where KCOV code could trigger recursive
faults, discovered while debugging a patch enabling KCOV for arch/arm:

* On CONFIG_PREEMPT kernels, there's a small race window where
  __sanitizer_cov_trace_pc() can see a bogus kcov_area.

* Lazy faulting of the vmalloc area can cause mutual recursion between
  fault handling code and __sanitizer_cov_trace_pc().

* During the context switch, switching the mm can cause the kcov_area to
  be transiently unmapped.

These are prerequisites for enabling KCOV on arm, but the issues
themsevles are generic -- we just happen to avoid them by chance rather
than design on x86-64 and arm64.

I've tested this on arm atop of v4.17-rc3, with KCOV enabled.


Mark Rutland (3):
  kcov: ensure irq code sees a valid area
  kcov: prefault the kcov_area
  sched/core / kcov: avoid kcov_area during task switch

 include/linux/kcov.h  | 14 ++++++++++++++
 include/linux/sched.h |  2 +-
 kernel/kcov.c         | 17 +++++++++++++++--
 kernel/sched/core.c   |  4 ++++
 4 files changed, 34 insertions(+), 3 deletions(-)