Commit 7d057943 authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Alexei Starovoitov
Browse files

selftests/bpf: verify states_equal() maintains idmap across all frames 



A test case that would erroneously pass verification if
verifier.c:states_equal() maintains separate register ID mappings for
call frames.

Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20221209135733.28851-5-eddyz87@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 5dd9cdbc

tools/testing/selftests/bpf/verifier/calls.c

+82 −0
Original line number Diff line number Diff line
@@ -2305,3 +2305,85 @@ 
	.errstr = "!read_ok",

	.result = REJECT,

},

/* Make sure that verifier.c:states_equal() considers IDs from all

 * frames when building 'idmap' for check_ids().

 */

{

	"calls: check_ids() across call boundary",

	.insns = {

	/* Function main() */

	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),

	/* fp[-24] = map_lookup_elem(...) ; get a MAP_VALUE_PTR_OR_NULL with some ID */

	BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),

	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),

	BPF_LD_MAP_FD(BPF_REG_1,

		      0),

	BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),

	BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_0, -24),

	/* fp[-32] = map_lookup_elem(...) ; get a MAP_VALUE_PTR_OR_NULL with some ID */

	BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),

	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),

	BPF_LD_MAP_FD(BPF_REG_1,

		      0),

	BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),

	BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_0, -32),

	/* call foo(&fp[-24], &fp[-32])   ; both arguments have IDs in the current

	 *                                ; stack frame

	 */

	BPF_MOV64_REG(BPF_REG_1, BPF_REG_FP),

	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -24),

	BPF_MOV64_REG(BPF_REG_2, BPF_REG_FP),

	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -32),

	BPF_CALL_REL(2),

	/* exit 0 */

	BPF_MOV64_IMM(BPF_REG_0, 0),

	BPF_EXIT_INSN(),

	/* Function foo()

	 *

	 * r9 = &frame[0].fp[-24]  ; save arguments in the callee saved registers,

	 * r8 = &frame[0].fp[-32]  ; arguments are pointers to pointers to map value

	 */

	BPF_MOV64_REG(BPF_REG_9, BPF_REG_1),

	BPF_MOV64_REG(BPF_REG_8, BPF_REG_2),

	/* r7 = ktime_get_ns() */

	BPF_EMIT_CALL(BPF_FUNC_ktime_get_ns),

	BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),

	/* r6 = ktime_get_ns() */

	BPF_EMIT_CALL(BPF_FUNC_ktime_get_ns),

	BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),

	/* if r6 > r7 goto +1      ; no new information about the state is derived from

	 *                         ; this check, thus produced verifier states differ

	 *                         ; only in 'insn_idx'

	 * r9 = r8

	 */

	BPF_JMP_REG(BPF_JGT, BPF_REG_6, BPF_REG_7, 1),

	BPF_MOV64_REG(BPF_REG_9, BPF_REG_8),

	/* r9 = *r9                ; verifier get's to this point via two paths:

	 *                         ; (I) one including r9 = r8, verified first;

	 *                         ; (II) one excluding r9 = r8, verified next.

	 *                         ; After load of *r9 to r9 the frame[0].fp[-24].id == r9.id.

	 *                         ; Suppose that checkpoint is created here via path (I).

	 *                         ; When verifying via (II) the r9.id must be compared against

	 *                         ; frame[0].fp[-24].id, otherwise (I) and (II) would be

	 *                         ; incorrectly deemed equivalent.

	 * if r9 == 0 goto <exit>

	 */

	BPF_LDX_MEM(BPF_DW, BPF_REG_9, BPF_REG_9, 0),

	BPF_JMP_IMM(BPF_JEQ, BPF_REG_9, 0, 1),

	/* r8 = *r8                ; read map value via r8, this is not safe

	 * r0 = *r8                ; because r8 might be not equal to r9.

	 */

	BPF_LDX_MEM(BPF_DW, BPF_REG_8, BPF_REG_8, 0),

	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_8, 0),

	/* exit 0 */

	BPF_MOV64_IMM(BPF_REG_0, 0),

	BPF_EXIT_INSN(),

	},

	.flags = BPF_F_TEST_STATE_FREQ,

	.fixup_map_hash_8b = { 3, 9 },

	.result = REJECT,

	.errstr = "R8 invalid mem access 'map_value_or_null'",

	.result_unpriv = REJECT,

	.errstr_unpriv = "",

	.prog_type = BPF_PROG_TYPE_CGROUP_SKB,

},