diff options
| author | Mark Rutland | 2018-06-14 15:27:37 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2018-06-15 07:55:24 +0900 |
| commit | dc55daff9040a90adce97208e776ee0bf515ab12 (patch) | |
| tree | 28b562c0d2a06c901e481d217b85cdf1a24723a6 | |
| parent | c9484b986ef03492357fddd50afbdd02929cfa72 (diff) | |
kcov: prefault the kcov_area
On many architectures the vmalloc area is lazily faulted in upon first
access. This is problematic for KCOV, as __sanitizer_cov_trace_pc
accesses the (vmalloc'd) kcov_area, and fault handling code may be
instrumented. If an access to kcov_area faults, this will result in
mutual recursion through the fault handling code and
__sanitizer_cov_trace_pc(), eventually leading to stack corruption
and/or overflow.
We can avoid this by faulting in the kcov_area before
__sanitizer_cov_trace_pc() is permitted to access it. Once it has been
faulted in, it will remain present in the process page tables, and will
not fault again.
[akpm@linux-foundation.org: code cleanup]
[akpm@linux-foundation.org: add comment explaining kcov_fault_in_area()]
[akpm@linux-foundation.org: fancier code comment from Mark]
Link: http://lkml.kernel.org/r/20180504135535.53744-3-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>
| -rw-r--r-- | kernel/kcov.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/kcov.c b/kernel/kcov.c index 5be9a60a959f..cf250392c55c 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -324,6 +324,21 @@ static int kcov_close(struct inode *inode, struct file *filep) return 0; } +/* + * Fault in a lazily-faulted vmalloc area before it can be used by + * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the + * vmalloc fault handling path is instrumented. + */ +static void kcov_fault_in_area(struct kcov *kcov) +{ + unsigned long stride = PAGE_SIZE / sizeof(unsigned long); + unsigned long *area = kcov->area; + unsigned long offset; + + for (offset = 0; offset < kcov->size; offset += stride) + READ_ONCE(area[offset]); +} + static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd, unsigned long arg) { @@ -372,6 +387,7 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd, #endif else return -EINVAL; + kcov_fault_in_area(kcov); /* Cache in task struct for performance. */ t->kcov_size = kcov->size; t->kcov_area = kcov->area; |