Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH 2/3] kcov: prefault the kcov_area | Date | Fri, 4 May 2018 14:55:34 +0100 |
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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.
Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Dmitry Vyukov <dvyukov@google.com> --- kernel/kcov.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/kernel/kcov.c b/kernel/kcov.c index 5be9a60a959f..3b82f8e258da 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -324,6 +324,17 @@ static int kcov_close(struct inode *inode, struct file *filep) return 0; } +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 +383,7 @@ 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; -- 2.11.0
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