kvm instrumentation: Fix kvm_mmio event NULL pointer dereference

Upstream Linux commit e39d200fa5bf ("KVM: Fix stack-out-of-bounds read
in write_mmio") introduce a NULL pointer check within TP_fast_assign().

lttng-modules commit 33630522da97 ("Update kvm instrumentation for 4.15")
introduce use of:

  ctf_sequence_hex(unsigned char, val, val, u32, len)

without the required NULL pointer check, which can trigger NULL pointer
dereference in case of unsatisfied MMIO read.

Add the missing NULL pointer check. Record a sequence of length 0 in the
trace when the val pointer is NULL.

Reported-by: Fahad Arslan <fahad.arslan@siemens.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I51a171a56af96e2cf68dba73f7eb473dd6c0ba0e

diff --git a/instrumentation/events/lttng-module/kvm.h b/instrumentation/events/lttng-module/kvm.h
index 814fb6139f24d9de58c916c09e7802eb4c96e68b..20e07aad9e36140c2d40ecceb91613a32c13f0ba 100644 (file)
--- a/instrumentation/events/lttng-module/kvm.h
+++ b/instrumentation/events/lttng-module/kvm.h
@@ -119,7 +119,7 @@ LTTNG_TRACEPOINT_EVENT(kvm_mmio,
                ctf_integer(u32, type, type)
                ctf_integer(u32, len, len)
                ctf_integer(u64, gpa, gpa)
-               ctf_sequence_hex(unsigned char, val, val, u32, len)
+               ctf_sequence_hex(unsigned char, val, val, u32, val != NULL ? len : 0)
        )
 )