On 12/13/24 3:29 PM, Amery Hung wrote:
Test referenced kptr acquired through struct_ops argument tagged with
"__ref". The success case checks whether 1) a reference to the correct
type is acquired, and 2) the referenced kptr argument can be accessed in
multiple paths as long as it hasn't been released. In the fail cases,
we first confirm that a referenced kptr acquried through a struct_ops
argument is not allowed to be leaked. Then, we make sure this new
referenced kptr acquiring mechanism does not accidentally allow referenced
kptrs to flow into global subprograms through their arguments.
Signed-off-by: Amery Hung <amery.hung@xxxxxxxxxxxxx>
---
.../selftests/bpf/bpf_testmod/bpf_testmod.c | 7 ++
.../selftests/bpf/bpf_testmod/bpf_testmod.h | 2 +
.../prog_tests/test_struct_ops_refcounted.c | 58 ++++++++++++++++
.../bpf/progs/struct_ops_refcounted.c | 67 +++++++++++++++++++
...ruct_ops_refcounted_fail__global_subprog.c | 32 +++++++++
.../struct_ops_refcounted_fail__ref_leak.c | 17 +++++
6 files changed, 183 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_refcounted.c
create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_refcounted.c
create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__global_subprog.c
create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__ref_leak.c
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 987d41af71d2..244234546ae2 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -1135,10 +1135,17 @@ static int bpf_testmod_ops__test_maybe_null(int dummy,
return 0;
}
+static int bpf_testmod_ops__test_refcounted(int dummy,
+ struct task_struct *task__ref)
+{
+ return 0;
+}
+
static struct bpf_testmod_ops __bpf_testmod_ops = {
.test_1 = bpf_testmod_test_1,
.test_2 = bpf_testmod_test_2,
.test_maybe_null = bpf_testmod_ops__test_maybe_null,
+ .test_refcounted = bpf_testmod_ops__test_refcounted,
};
struct bpf_struct_ops bpf_bpf_testmod_ops = {
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
index fb7dff47597a..0e31586c1353 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
@@ -36,6 +36,8 @@ struct bpf_testmod_ops {
/* Used to test nullable arguments. */
int (*test_maybe_null)(int dummy, struct task_struct *task);
int (*unsupported_ops)(void);
+ /* Used to test ref_acquired arguments. */
+ int (*test_refcounted)(int dummy, struct task_struct *task);
/* The following fields are used to test shadow copies. */
char onebyte;
diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_refcounted.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_refcounted.c
new file mode 100644
index 000000000000..976df951b700
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_refcounted.c
@@ -0,0 +1,58 @@
+#include <test_progs.h>
+
+#include "struct_ops_refcounted.skel.h"
+#include "struct_ops_refcounted_fail__ref_leak.skel.h"
+#include "struct_ops_refcounted_fail__global_subprog.skel.h"
+
+/* Test that the verifier accepts a program that first acquires a referenced
+ * kptr through context and then releases the reference
+ */
+static void refcounted(void)
+{
+ struct struct_ops_refcounted *skel;
+
+ skel = struct_ops_refcounted__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "struct_ops_module_open_and_load"))
+ return;
+
+ struct_ops_refcounted__destroy(skel);
+}
+
+/* Test that the verifier rejects a program that acquires a referenced
+ * kptr through context without releasing the reference
+ */
+static void refcounted_fail__ref_leak(void)
+{
+ struct struct_ops_refcounted_fail__ref_leak *skel;
+
+ skel = struct_ops_refcounted_fail__ref_leak__open_and_load();
+ if (ASSERT_ERR_PTR(skel, "struct_ops_module_fail__open_and_load"))
+ return;
+
+ struct_ops_refcounted_fail__ref_leak__destroy(skel);
+}
+
+/* Test that the verifier rejects a program that contains a global
+ * subprogram with referenced kptr arguments
+ */
+static void refcounted_fail__global_subprog(void)
+{
+ struct struct_ops_refcounted_fail__global_subprog *skel;
+
+ skel = struct_ops_refcounted_fail__global_subprog__open_and_load();
+ if (ASSERT_ERR_PTR(skel, "struct_ops_module_fail__open_and_load"))
+ return;
+
+ struct_ops_refcounted_fail__global_subprog__destroy(skel);
+}
+
+void test_struct_ops_refcounted(void)
+{
+ if (test__start_subtest("refcounted"))
+ refcounted();
+ if (test__start_subtest("refcounted_fail__ref_leak"))
+ refcounted_fail__ref_leak();
+ if (test__start_subtest("refcounted_fail__global_subprog"))
+ refcounted_fail__global_subprog();
+}
+
diff --git a/tools/testing/selftests/bpf/progs/struct_ops_refcounted.c b/tools/testing/selftests/bpf/progs/struct_ops_refcounted.c
new file mode 100644
index 000000000000..2c1326668b92
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/struct_ops_refcounted.c
@@ -0,0 +1,67 @@
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "../bpf_testmod/bpf_testmod.h"
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+extern void bpf_task_release(struct task_struct *p) __ksym;
+
+/* This is a test BPF program that uses struct_ops to access a referenced
+ * kptr argument. This is a test for the verifier to ensure that it
+ * 1) recongnizes the task as a referenced object (i.e., ref_obj_id > 0), and
+ * 2) the same reference can be acquired from multiple paths as long as it
+ * has not been released.
+ *
+ * test_refcounted() is equivalent to the C code below. It is written in assembly
+ * to avoid reads from task (i.e., getting referenced kptrs to task) being merged
+ * into single path by the compiler.
+ *
+ * int test_refcounted(int dummy, struct task_struct *task)
+ * {
+ * if (dummy % 2)
+ * bpf_task_release(task);
+ * else
+ * bpf_task_release(task);
+ * return 0;
+ * }
+ */
+SEC("struct_ops/test_refcounted")
+int test_refcounted(unsigned long long *ctx)
+{
+ asm volatile (" \
+ /* r6 = dummy */ \
+ r6 = *(u64 *)(r1 + 0x0); \
+ /* if (r6 & 0x1 != 0) */ \
+ r6 &= 0x1; \
+ if r6 == 0 goto l0_%=; \
+ /* r1 = task */ \
+ r1 = *(u64 *)(r1 + 0x8); \
+ call %[bpf_task_release]; \
+ goto l1_%=; \
+l0_%=: /* r1 = task */ \
+ r1 = *(u64 *)(r1 + 0x8); \
+ call %[bpf_task_release]; \
+l1_%=: /* return 0 */ \
+" :
+ : __imm(bpf_task_release)
+ : __clobber_all);
+ return 0;
+}
You can use clang nomerge attribute to prevent bpf_task_release(task) merging. For example,
$ cat t.c
struct task_struct {
int a;
int b;
int d[20];
};
__attribute__((nomerge)) extern void bpf_task_release(struct task_struct *task);
int test_refcounted(int dummy, struct task_struct *task)
{
if (dummy % 2)
bpf_task_release(task);
else
bpf_task_release(task);
return 0;
}
$ clang --version
clang version 19.1.5 (https://github.com/llvm/llvm-project.git ab4b5a2db582958af1ee308a790cfdb42bd24720)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/yhs/work/llvm-project/llvm/build.19/Release/bin
$ clang --target=bpf -O2 -mcpu=v3 -S t.c
$ cat t.s
.text
.file "t.c"
.globl test_refcounted # -- Begin function test_refcounted
.p2align 3
.type test_refcounted,@function
test_refcounted: # @test_refcounted
# %bb.0:
w1 &= 1
if w1 == 0 goto LBB0_2
# %bb.1:
r1 = r2
call bpf_task_release
goto LBB0_3
LBB0_2:
r1 = r2
call bpf_task_release
LBB0_3:
w0 = 0
exit
.Lfunc_end0:
.size test_refcounted, .Lfunc_end0-test_refcounted
# -- End function
.addrsig
+
+/* BTF FUNC records are not generated for kfuncs referenced
+ * from inline assembly. These records are necessary for
+ * libbpf to link the program. The function below is a hack
+ * to ensure that BTF FUNC records are generated.
+ */
+void __btf_root(void)
+{
+ bpf_task_release(NULL);
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops testmod_refcounted = {
+ .test_refcounted = (void *)test_refcounted,
+};
+
+
diff --git a/tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__global_subprog.c b/tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__global_subprog.c
new file mode 100644
index 000000000000..c7e84e63b053
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__global_subprog.c
@@ -0,0 +1,32 @@
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "../bpf_testmod/bpf_testmod.h"
+
+char _license[] SEC("license") = "GPL";
+
+extern void bpf_task_release(struct task_struct *p) __ksym;
+
+__noinline int subprog_release(__u64 *ctx __arg_ctx)
+{
+ struct task_struct *task = (struct task_struct *)ctx[1];
+ int dummy = (int)ctx[0];
+
+ bpf_task_release(task);
+
+ return dummy + 1;
+}
+
+SEC("struct_ops/test_refcounted")
+int test_refcounted(unsigned long long *ctx)
+{
+ struct task_struct *task = (struct task_struct *)ctx[1];
+
+ bpf_task_release(task);
+
+ return subprog_release(ctx);
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops testmod_ref_acquire = {
+ .test_refcounted = (void *)test_refcounted,
+};
diff --git a/tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__ref_leak.c b/tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__ref_leak.c
new file mode 100644
index 000000000000..6e82859eb187
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/struct_ops_refcounted_fail__ref_leak.c
@@ -0,0 +1,17 @@
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "../bpf_testmod/bpf_testmod.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("struct_ops/test_refcounted")
+int BPF_PROG(test_refcounted, int dummy,
+ struct task_struct *task)
+{
+ return 0;
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops testmod_ref_acquire = {
+ .test_refcounted = (void *)test_refcounted,
+};
