[DTrace-devel] [PATCH v2] error: ERROR probe firing should not corrupt probe arguments

[Kris Van Hees]

When an ERROR probe fires due to a fault happening while processing a
probe firing, it was corrupting the first 6 probe arguments of the
probe causing the fault because they were being overwritten.  But since
a fault only aborts the execution of the clause it occurs in, those
original probe arguments might still be needed for other clauses that
are executed for the original probe.

Save arg0 through arg5 prior to calling the ERROR probe, and restore
them after the ERROR probe finishes.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 bpf/probe_error.c                             |  3 ++
 libdtrace/dt_dctx.h                           |  1 +
 .../error/tst.argv-corruption-by-error.d      | 48 +++++++++++++++++++
 3 files changed, 52 insertions(+)
 create mode 100644 test/unittest/error/tst.argv-corruption-by-error.d

diff --git a/bpf/probe_error.c b/bpf/probe_error.c
index c8ddcdfa..8d631704 100644
--- a/bpf/probe_error.c
+++ b/bpf/probe_error.c
@@ -26,7 +26,9 @@ noinline void dt_probe_error(const dt_dctx_t *dctx, uint64_t pc, uint64_t fault,
 			     uint64_t illval)
 {
 	dt_mstate_t	*mst = dctx->mst;
+	uint64_t	argv[6];
 
+	__builtin_memcpy(mst->error_argv, mst->argv, sizeof(mst->error_argv));
 	mst->argv[0] = 0;
 	mst->argv[1] = mst->epid;
 	mst->argv[2] = mst->clid;
@@ -36,5 +38,6 @@ noinline void dt_probe_error(const dt_dctx_t *dctx, uint64_t pc, uint64_t fault,
 
 	dt_error(dctx);
 
+	__builtin_memcpy(mst->argv, mst->error_argv, sizeof(mst->error_argv));
 	mst->fault = fault;
 }
diff --git a/libdtrace/dt_dctx.h b/libdtrace/dt_dctx.h
index 1422ad24..9f33f1fb 100644
--- a/libdtrace/dt_dctx.h
+++ b/libdtrace/dt_dctx.h
@@ -31,6 +31,7 @@ typedef struct dt_mstate {
 	dt_pt_regs	regs;		/* CPU registers */
 	uint64_t	argv[10];	/* Probe arguments */
 	uint64_t	saved_argv[10];	/* Saved probe arguments */
+	uint64_t	error_argv[6];	/* ERROR probe saved arguments */
 } dt_mstate_t;
 
 #define DMST_EPID		offsetof(dt_mstate_t, epid)
diff --git a/test/unittest/error/tst.argv-corruption-by-error.d b/test/unittest/error/tst.argv-corruption-by-error.d
new file mode 100644
index 00000000..6fd1834e
--- /dev/null
+++ b/test/unittest/error/tst.argv-corruption-by-error.d
@@ -0,0 +1,48 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+/*
+ * ASSERTION: A fault that triggers the ERROR probe terminates the execution of
+ *            the current clause, while other clauses for the same probe should
+ *            still be executed.  This tests that the ERROR probe invocation
+ *            does not corrupt the arguments of the original probe.
+ *
+ * SECTION: dtrace Provider
+ */
+
+#pragma D option quiet
+
+syscall::write*:entry
+{
+	self->arg0 = arg0;
+	self->arg1 = arg1;
+	self->arg2 = arg2;
+	self->arg3 = arg3;
+	self->arg4 = arg4;
+	self->arg5 = arg5;
+
+	printf("%d / %d / %d / %d / %d / %d\n",
+	       arg0, arg1, arg2, arg3, arg4, arg5);
+}
+
+syscall::write*:entry
+{
+	trace(*(int *)0);
+}
+
+syscall::write*:entry,
+ERROR {
+	printf("%d / %d / %d / %d / %d / %d\n",
+	       arg0, arg1, arg2, arg3, arg4, arg5);
+}
+
+syscall::write*:entry
+{
+	exit(self->arg0 != arg0 || self->arg1 != arg1 || self->arg2 != arg2 ||
+	     self->arg3 != arg3 || self->arg4 != arg4 || self->arg5 != arg5
+		? 1 : 0);
+}
-- 
2.45.2