[PATCH bpf-next v3 0/2] bpf: Enforce gotox targets against subprog bounds

[PATCH bpf-next v3 0/2] bpf: Enforce gotox targets against subprog bounds

[Nuoqi Gui]

For gotox, CFG construction models the indirect-jump target set in
insn_aux_data->jt, while do_check() later follows targets from the runtime
PTR_TO_INSN register's own INSN_ARRAY map. If the same gotox can be
reached with PTR_TO_INSN values from different maps, do_check() can accept
a target outside the calling subprog.

The observed x86 JIT case can then enter another subprog without a matching
BPF call frame and crash when the program is run.

Fix this by rejecting gotox map targets outside the current gotox subprog.
Add a regression test covering the two-map cross-subprog case.

v1 -> v2:
  - Validate gotox runtime targets against the current subprog bounds instead
    of scanning the CFG jump table.
  - Fix the selftest expected error from -EACCES to -EINVAL.

v2 -> v3:
  - Drop the Validation section from the cover letter.
  - Clarify that the crash was observed through the x86 JIT path while the
    verifier invariant is generic.
  - Simplify the cover letter and commit message.
  - Remove the unused skel argument from the raw-insn selftest.
  - Move the raw-insn selftest to the end of test_bpf_gotox().

v1:
  https://lore.kernel.org/bpf/20260609-f01-03-gotox-bpf-next-v1-0-b441d63a1559@mails.tsinghua.edu.cn/

v2:
  https://lore.kernel.org/bpf/20260613-f01-03-gotox-bpf-next-v2-send-v2-0-7c883b43f3c3@mails.tsinghua.edu.cn/

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
---
Nuoqi Gui (2):
      bpf: Enforce gotox targets against subprog bounds
      selftests/bpf: Add cross-subprog gotox target coverage

 kernel/bpf/verifier.c                              | 19 ++++++
 tools/testing/selftests/bpf/prog_tests/bpf_gotox.c | 73 ++++++++++++++++++++++
 2 files changed, 92 insertions(+)
---
base-commit: 7bfb93e3475be9de894f1cecd3a727d3e1649b03
change-id: 20260628-f01-03-gotox-bpf-next-1a7af91d2c82

Best regards,
--  
Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>

[PATCH bpf-next v3 1/2] bpf: Enforce gotox targets against subprog bounds

[Nuoqi Gui]

During CFG construction, the verifier records the modeled gotox target set
in insn_aux_data->jt. Later, check_indirect_jump() follows targets from
the runtime PTR_TO_INSN register's actual INSN_ARRAY map.

This lets one gotox instruction observe different INSN_ARRAY maps on
different paths and accept a target outside the calling subprog. The
observed x86 JIT case can then enter another subprog without a matching
BPF call frame and crash when executed.

Reject every target copied from the actual PTR_TO_INSN map if it is
outside the calling subprog.

Fixes: 493d9e0d6083 ("bpf, x86: add support for indirect jumps")
Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
---
 kernel/bpf/verifier.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index eb46a81a8c51..05a996a5ecdd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17145,9 +17145,11 @@ static int indirect_jump_min_max_index(struct bpf_verifier_env *env,
 static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *insn)
 {
 	struct bpf_verifier_state *other_branch;
+	struct bpf_subprog_info *subprog;
 	struct bpf_reg_state *dst_reg;
 	struct bpf_map *map;
 	u32 min_index, max_index;
+	int subprog_start, subprog_end;
 	int err = 0;
 	int n;
 	int i;
@@ -17188,6 +17190,23 @@ static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *in
 		return -EINVAL;
 	}
 
+	subprog = bpf_find_containing_subprog(env, env->insn_idx);
+	if (verifier_bug_if(!subprog, env,
+			    "gotox insn %d is outside subprog bounds\n",
+			    env->insn_idx))
+		return -EFAULT;
+	subprog_start = subprog->start;
+	subprog_end = (subprog + 1)->start;
+
+	for (i = 0; i < n; i++) {
+		u32 target = env->gotox_tmp_buf->items[i];
+
+		if (target < subprog_start || target >= subprog_end) {
+			verbose(env, "gotox target %u outside subprog\n", target);
+			return -EINVAL;
+		}
+	}
+
 	for (i = 0; i < n - 1; i++) {
 		mark_indirect_target(env, env->gotox_tmp_buf->items[i]);
 		other_branch = push_stack(env, env->gotox_tmp_buf->items[i],

-- 
2.34.1

Re: [PATCH bpf-next v3 1/2] bpf: Enforce gotox targets against subprog bounds

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [Critical] The patch adds a runtime bounds check to prevent `gotox` targets from jumping outside the current subprogram, but fails to ensure that dynamically observed targets were actually modeled during Control Flow Graph (CFG) construction. This allows an attacker to follow unmodeled control-flow edges and bypass static liveness-based state pruning.
--

commit 5e0bdd5b4a7e2ce073913482349669d9387d6a32
Author: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>

bpf: Enforce gotox targets against subprog bounds

During CFG construction, the verifier records the modeled gotox target set
in insn_aux_data->jt. This patch adds a check to reject targets outside the
calling subprogram bounds when check_indirect_jump() follows targets from
the runtime PTR_TO_INSN register's actual INSN_ARRAY map.

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
[ ... ]
> @@ -17188,6 +17190,23 @@ static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *in
>  		return -EINVAL;
>  	}
>  
> +	subprog = bpf_find_containing_subprog(env, env->insn_idx);
> +	if (verifier_bug_if(!subprog, env,
> +			    "gotox insn %d is outside subprog bounds\n",
> +			    env->insn_idx))
> +		return -EFAULT;
> +	subprog_start = subprog->start;
> +	subprog_end = (subprog + 1)->start;
> +
> +	for (i = 0; i < n; i++) {
> +		u32 target = env->gotox_tmp_buf->items[i];
> +
> +		if (target < subprog_start || target >= subprog_end) {

[Severity: Critical]
This is a pre-existing issue, but does this bounds check alone fully protect
against unmodeled control-flow edges?

During CFG construction in kernel/bpf/cfg.c:jt_from_subprog(), if an
INSN_ARRAY map's minimum offset falls outside the subprogram, the heuristic
skips the map entirely:

    if (jt_cur->items[0] >= subprog_start && jt_cur->items[0] < subprog_end) {

If an attacker creates an INSN_ARRAY map containing both an out-of-bounds
offset (e.g., 0) and a valid in-bounds target Y, the CFG construction drops
Y completely because items[0] is less than subprog_start.

Later at runtime, if the attacker restricts the bounds to index exactly Y,
this check passes because Y is within subprog_start and subprog_end. The
verifier then explores the gotox to Y edge that was never modeled in the
CFG jump tables.

Because liveness analysis relies strictly on the statically modeled CFG,
could traversing this unmodeled edge cause liveness to incorrectly assume
registers are dead, allowing an unsound state pruning bypass?

Should this logic verify that the dynamic target is actually present in
env->insn_aux_data[env->insn_idx].jt, rather than only verifying the target
is within subprogram boundaries?

> +			verbose(env, "gotox target %u outside subprog\n", target);
> +			return -EINVAL;
> +		}
> +	}
> +

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260628-f01-03-gotox-bpf-next-v3-0-b744432e1361@mails.tsinghua.edu.cn?part=1

[PATCH bpf-next v3 2/2] selftests/bpf: Add cross-subprog gotox target coverage

[Nuoqi Gui]

Add a gotox regression test with two one-entry INSN_ARRAY maps. CFG can
model a map whose target stays in the main subprog, while the verified path
can load a different map whose target is the first instruction of another
subprog.

That second target is outside the subprog that contains this gotox
instruction, so program load must be rejected with -EINVAL.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
---
 tools/testing/selftests/bpf/prog_tests/bpf_gotox.c | 73 ++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c b/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c
index 73dc63882b7d..997724c61c8b 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_gotox.c
@@ -255,6 +255,30 @@ static int create_jt_map(__u32 max_entries)
 			      key_size, value_size, max_entries, NULL);
 }
 
+static int create_jt_map_with_target(__u32 target)
+{
+	struct bpf_insn_array_value val = { .orig_off = target };
+	__u32 key = 0;
+	int map_fd;
+
+	map_fd = create_jt_map(1);
+	if (!ASSERT_GE(map_fd, 0, "create_jt_map"))
+		return -1;
+
+	if (!ASSERT_EQ(bpf_map_update_elem(map_fd, &key, &val, 0),
+		       0, "bpf_map_update_elem")) {
+		close(map_fd);
+		return -1;
+	}
+
+	if (!ASSERT_EQ(bpf_map_freeze(map_fd), 0, "bpf_map_freeze")) {
+		close(map_fd);
+		return -1;
+	}
+
+	return map_fd;
+}
+
 static int prog_load(struct bpf_insn *insns, __u32 insn_cnt)
 {
 	return bpf_prog_load(BPF_PROG_TYPE_RAW_TRACEPOINT, NULL, "GPL", insns, insn_cnt, NULL);
@@ -393,6 +417,52 @@ reject_offsets(struct bpf_insn *insns, __u32 insn_cnt, int off1, int off2, int o
 		close(prog_fd);
 }
 
+static void
+check_cross_subprog_gotox_target(void)
+{
+	struct bpf_insn insns[] = {
+		/* main subprog [0,14) */
+		BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_CALL, 0, 12),
+		BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_6, 0),
+		BPF_JMP_IMM(BPF_JEQ, BPF_REG_7, 0, 4),
+		BPF_LD_IMM64_RAW(BPF_REG_2, BPF_PSEUDO_MAP_VALUE, 0),
+		BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_2, 0),
+		BPF_JMP_A(3),
+		BPF_LD_IMM64_RAW(BPF_REG_2, BPF_PSEUDO_MAP_VALUE, 0),
+		BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_2, 0),
+		BPF_RAW_INSN(BPF_JMP | BPF_JA | BPF_X, BPF_REG_2, 0, 0, 0),
+		BPF_MOV64_IMM(BPF_REG_0, 1),
+		BPF_EXIT_INSN(),
+
+		/* static subprog [14,16) */
+		BPF_MOV64_IMM(BPF_REG_0, 42),
+		BPF_EXIT_INSN(),
+	};
+	int good_fd, bad_fd, prog_fd;
+
+	good_fd = create_jt_map_with_target(12);
+	if (!ASSERT_GE(good_fd, 0, "create_good_jt_map"))
+		return;
+
+	bad_fd = create_jt_map_with_target(14);
+	if (!ASSERT_GE(bad_fd, 0, "create_bad_jt_map")) {
+		close(good_fd);
+		return;
+	}
+
+	insns[4].imm = bad_fd;
+	insns[8].imm = good_fd;
+
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL",
+				insns, ARRAY_SIZE(insns), NULL);
+	if (!ASSERT_EQ(prog_fd, -EINVAL, "cross_subprog_gotox_prog_load"))
+		close(prog_fd);
+
+	close(bad_fd);
+	close(good_fd);
+}
+
 /*
  * Verify a bit more complex programs which include indirect jumps
  * and with jump tables loaded with a non-zero offset
@@ -541,5 +611,8 @@ void test_bpf_gotox(void)
 	if (test__start_subtest("check-ldimm64-off-gotox-llvm"))
 		__subtest(skel, check_ldimm64_off_gotox_llvm);
 
+	if (test__start_subtest("check-cross-subprog-gotox-target"))
+		check_cross_subprog_gotox_target();
+
 	bpf_gotox__destroy(skel);
 }

-- 
2.34.1