[PATCH 4.19 133/293] selftests/bpf: Test variable offset stack access

[Greg Kroah-Hartman]

From: Andrey Ignatov <rdna@xxxxxx>

commit 8ff80e96e3ccea5ff0a890d4f18997e0344dbec2 upstream.

Test different scenarios of indirect variable-offset stack access: out of
bound access (>0), min_off below initialized part of the stack,
max_off+size above initialized part of the stack, initialized stack.

Example of output:
  ...
  #856/p indirect variable-offset stack access, out of bound OK
  #857/p indirect variable-offset stack access, max_off+size > max_initialized OK
  #858/p indirect variable-offset stack access, min_off < min_initialized OK
  #859/p indirect variable-offset stack access, ok OK
  ...

Signed-off-by: Andrey Ignatov <rdna@xxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
[OP: backport to 4.19]
Signed-off-by: Ovidiu Panait <ovidiu.panait@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 tools/testing/selftests/bpf/test_verifier.c |   79 +++++++++++++++++++++++++++-
 1 file changed, 77 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -8495,7 +8495,7 @@ static struct bpf_test tests[] = {
 		.prog_type = BPF_PROG_TYPE_LWT_IN,
 	},
 	{
-		"indirect variable-offset stack access",
+		"indirect variable-offset stack access, out of bound",
 		.insns = {
 			/* Fill the top 8 bytes of the stack */
 			BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
@@ -8516,11 +8516,86 @@ static struct bpf_test tests[] = {
 			BPF_EXIT_INSN(),
 		},
 		.fixup_map1 = { 5 },
-		.errstr = "variable stack read R2",
+		.errstr = "invalid stack type R2 var_off",
 		.result = REJECT,
 		.prog_type = BPF_PROG_TYPE_LWT_IN,
 	},
 	{
+		"indirect variable-offset stack access, max_off+size > max_initialized",
+		.insns = {
+		/* Fill only the second from top 8 bytes of the stack. */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
+		/* Get an unknown value. */
+		BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
+		/* Make it small and 4-byte aligned. */
+		BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
+		BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16),
+		/* Add it to fp.  We now have either fp-12 or fp-16, but we don't know
+		 * which. fp-12 size 8 is partially uninitialized stack.
+		 */
+		BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
+		/* Dereference it indirectly. */
+		BPF_LD_MAP_FD(BPF_REG_1, 0),
+		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+		},
+		.fixup_map1 = { 5 },
+		.errstr = "invalid indirect read from stack var_off",
+		.result = REJECT,
+		.prog_type = BPF_PROG_TYPE_LWT_IN,
+	},
+	{
+		"indirect variable-offset stack access, min_off < min_initialized",
+		.insns = {
+		/* Fill only the top 8 bytes of the stack. */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
+		/* Get an unknown value */
+		BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
+		/* Make it small and 4-byte aligned. */
+		BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
+		BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16),
+		/* Add it to fp.  We now have either fp-12 or fp-16, but we don't know
+		 * which. fp-16 size 8 is partially uninitialized stack.
+		 */
+		BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
+		/* Dereference it indirectly. */
+		BPF_LD_MAP_FD(BPF_REG_1, 0),
+		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+		},
+		.fixup_map1 = { 5 },
+		.errstr = "invalid indirect read from stack var_off",
+		.result = REJECT,
+		.prog_type = BPF_PROG_TYPE_LWT_IN,
+	},
+	{
+		"indirect variable-offset stack access, ok",
+		.insns = {
+		/* Fill the top 16 bytes of the stack. */
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
+		BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
+		/* Get an unknown value. */
+		BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
+		/* Make it small and 4-byte aligned. */
+		BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
+		BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 16),
+		/* Add it to fp.  We now have either fp-12 or fp-16, we don't know
+		 * which, but either way it points to initialized stack.
+		 */
+		BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
+		/* Dereference it indirectly. */
+		BPF_LD_MAP_FD(BPF_REG_1, 0),
+		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+		},
+		.fixup_map1 = { 6 },
+		.result = ACCEPT,
+		.prog_type = BPF_PROG_TYPE_LWT_IN,
+	},
+	{
 		"direct stack access with 32-bit wraparound. test1",
 		.insns = {
 			BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),