[PATCH bpf-next 2/2] selftests/bpf: Tests for uninitialized stack reads

[Eduard Zingerman <eddyz87@gmail.com>]

Two testcases to make sure that stack reads from uninitialized
locations are accepted by verifier when executed in privileged mode:
- read from a fixed offset;
- read from a variable offset.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 .../selftests/bpf/prog_tests/uninit_stack.c   |  9 +++
 .../selftests/bpf/progs/uninit_stack.c        | 55 +++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/uninit_stack.c
 create mode 100644 tools/testing/selftests/bpf/progs/uninit_stack.c

diff --git a/tools/testing/selftests/bpf/prog_tests/uninit_stack.c b/tools/testing/selftests/bpf/prog_tests/uninit_stack.c
new file mode 100644
index 000000000000..e64c71948491
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/uninit_stack.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "uninit_stack.skel.h"
+
+void test_uninit_stack(void)
+{
+	RUN_TESTS(uninit_stack);
+}
diff --git a/tools/testing/selftests/bpf/progs/uninit_stack.c b/tools/testing/selftests/bpf/progs/uninit_stack.c
new file mode 100644
index 000000000000..20ff6a22c906
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/uninit_stack.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+/* Read an uninitialized value from stack at a fixed offset */
+SEC("socket")
+__naked int read_uninit_stack_fixed_off(void *ctx)
+{
+	asm volatile ("				\
+		// force stack depth to be 128	\
+		*(u64*)(r10 - 128) = r1;	\
+		r1 = *(u8 *)(r10 - 8 );		\
+		r1 = *(u8 *)(r10 - 11);		\
+		r1 = *(u8 *)(r10 - 13);		\
+		r1 = *(u8 *)(r10 - 15);		\
+		r1 = *(u16*)(r10 - 16);		\
+		r1 = *(u32*)(r10 - 32);		\
+		r1 = *(u64*)(r10 - 64);		\
+		// read from a spill of a wrong size, it is a separate	\
+		// branch in check_stack_read_fixed_off()		\
+		*(u32*)(r10 - 72) = r1;		\
+		r1 = *(u64*)(r10 - 72);		\
+		r0 = 0;				\
+		exit;				\
+"
+		      ::: __clobber_all);
+}
+
+/* Read an uninitialized value from stack at a variable offset */
+SEC("socket")
+__naked int read_uninit_stack_var_off(void *ctx)
+{
+	asm volatile ("				\
+		call %[bpf_get_prandom_u32];	\
+		// force stack depth to be 64	\
+		*(u64*)(r10 - 64) = r0;		\
+		r0 = -r0;			\
+		// give r0 a range [-31, -1]	\
+		if r0 s<= -32 goto exit_%=;	\
+		if r0 s>= 0 goto exit_%=;	\
+		// access stack using r0	\
+		r1 = r10;			\
+		r1 += r0;			\
+		r2 = *(u8*)(r1 + 0);		\
+exit_%=:	r0 = 0;				\
+		exit;				\
+"
+		      :
+		      : __imm(bpf_get_prandom_u32)
+		      : __clobber_all);
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.39.1