The patch titled
Subject: kcov: prefault the kcov_area
has been added to the -mm tree. Its filename is
kcov-prefault-the-kcov_area.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kcov-prefault-the-kcov_area.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kcov-prefault-the-kcov_area.patch
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------------------------------------------------------
From: Mark Rutland <mark.rutland@xxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20180504135535.53744-3-mark.rutland@xxxxxxx
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Acked-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/kcov.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff -puN kernel/kcov.c~kcov-prefault-the-kcov_area kernel/kcov.c
--- a/kernel/kcov.c~kcov-prefault-the-kcov_area
+++ a/kernel/kcov.c
@@ -324,6 +324,17 @@ static int kcov_close(struct inode *inod
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
#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;
_
Patches currently in -mm which might be from mark.rutland@xxxxxxx are
kcov-ensure-irq-code-sees-a-valid-area.patch
kcov-prefault-the-kcov_area.patch
sched-core-kcov-avoid-kcov_area-during-task-switch.patch
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