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author | Mark Rutland <mark.rutland@arm.com> | 2018-06-14 15:27:34 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-06-15 07:55:24 +0900 |
commit | c9484b986ef03492357fddd50afbdd02929cfa72 (patch) | |
tree | 8862085259d71aa45f05980834166776ca2670ea /kernel | |
parent | 3fb3894b84c2e0f83cb1e4f4e960243742e6b3a6 (diff) | |
download | linux-c9484b986ef03492357fddd50afbdd02929cfa72.tar.gz linux-c9484b986ef03492357fddd50afbdd02929cfa72.tar.bz2 linux-c9484b986ef03492357fddd50afbdd02929cfa72.zip |
kcov: ensure irq code sees a valid area
Patch series "kcov: fix unexpected faults".
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.
This patch (of 3):
For kernels built with CONFIG_PREEMPT, some C code may execute before or
after the interrupt handler, while the hardirq count is zero. In these
cases, in_task() can return true.
A task can be interrupted in the middle of a KCOV_DISABLE ioctl while it
resets the task's kcov data via kcov_task_init(). Instrumented code
executed during this period will call __sanitizer_cov_trace_pc(), and as
in_task() returns true, will inspect t->kcov_mode before trying to write
to t->kcov_area.
In kcov_init_task() we update t->kcov_{mode,area,size} with plain stores,
which may be re-ordered, torn, etc. Thus __sanitizer_cov_trace_pc() may
see bogus values for any of these fields, and may attempt to write to
memory which is not mapped.
Let's avoid this by using WRITE_ONCE() to set t->kcov_mode, with a
barrier() to ensure this is ordered before we clear t->kov_{area,size}.
This ensures that any code execute while kcov_init_task() is preempted
will either see valid values for t->kcov_{area,size}, or will see that
t->kcov_mode is KCOV_MODE_DISABLED, and bail out without touching
t->kcov_area.
Link: http://lkml.kernel.org/r/20180504135535.53744-2-mark.rutland@arm.com
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/kcov.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/kcov.c b/kernel/kcov.c index 2c16f1ab5e10..5be9a60a959f 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -241,7 +241,8 @@ static void kcov_put(struct kcov *kcov) void kcov_task_init(struct task_struct *t) { - t->kcov_mode = KCOV_MODE_DISABLED; + WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED); + barrier(); t->kcov_size = 0; t->kcov_area = NULL; t->kcov = NULL; |