selftests/bpf: Add tests for the KF_PERFMON gates

Add test cases where each one loads with CAP_BPF alone and checks that
the program is correctly rejected.

  # LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t verifier_kfunc_perfmon
  [...]
  #627/1   verifier_kfunc_perfmon/rdonly_cast_noperfmon:OK
  #627/2   verifier_kfunc_perfmon/rdonly_cast_noperfmon @unpriv:OK
  #627/3   verifier_kfunc_perfmon/probe_read_kernel_dynptr_noperfmon:OK
  #627/4   verifier_kfunc_perfmon/probe_read_kernel_dynptr_noperfmon @unpriv:OK
  #627/5   verifier_kfunc_perfmon/stream_vprintk_noperfmon:OK
  #627/6   verifier_kfunc_perfmon/stream_vprintk_noperfmon @unpriv:OK
  #627/7   verifier_kfunc_perfmon/get_kmem_cache_noperfmon:OK
  #627/8   verifier_kfunc_perfmon/get_kmem_cache_noperfmon @unpriv:OK
  #627/9   verifier_kfunc_perfmon/arg_untrusted_read_noperfmon:OK
  #627/10  verifier_kfunc_perfmon/arg_untrusted_read_noperfmon @unpriv:OK
  #627     verifier_kfunc_perfmon:OK
  Summary: 1/10 PASSED, 0 SKIPPED, 0/0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260910213510.49358-4-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -53,6 +53,7 @@
 #include "verifier_iterating_callbacks.skel.h"
 #include "verifier_jeq_infer_not_null.skel.h"
 #include "verifier_jit_convergence.skel.h"
+#include "verifier_kfunc_perfmon.skel.h"
 #include "verifier_ld_ind.skel.h"
 #include "verifier_ldsx.skel.h"
 #include "verifier_leak_ptr.skel.h"
@@ -216,6 +217,7 @@ void test_verifier_int_ptr(void)              { RUN(verifier_int_ptr); }
 void test_verifier_iterating_callbacks(void)  { RUN(verifier_iterating_callbacks); }
 void test_verifier_jeq_infer_not_null(void)   { RUN(verifier_jeq_infer_not_null); }
 void test_verifier_jit_convergence(void)      { RUN(verifier_jit_convergence); }
+void test_verifier_kfunc_perfmon(void)        { RUN(verifier_kfunc_perfmon); }
 void test_verifier_load_acquire(void)         { RUN(verifier_load_acquire); }
 void test_verifier_ld_ind(void)               { RUN(verifier_ld_ind); }
 void test_verifier_ldsx(void)                  { RUN(verifier_ldsx); }

tools/testing/selftests/bpf/progs/verifier_kfunc_perfmon.c

@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+void *user_ptr;
+char dynptr_buf[8];
+u64 kaddr;
+
+extern struct kmem_cache *bpf_get_kmem_cache(u64 addr) __ksym;
+
+SEC("socket")
+__success
+__caps_unpriv(CAP_BPF)
+__failure_unpriv
+__msg_unpriv("bpf_rdonly_cast is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
+int rdonly_cast_noperfmon(void *ctx)
+{
+	char *p = bpf_rdonly_cast(0, 0);
+
+	return p[0x7fff];
+}
+
+SEC("socket")
+__success
+__caps_unpriv(CAP_BPF)
+__failure_unpriv
+__msg_unpriv("bpf_probe_read_kernel_dynptr is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
+int probe_read_kernel_dynptr_noperfmon(void *ctx)
+{
+	struct bpf_dynptr dptr;
+
+	bpf_dynptr_from_mem(dynptr_buf, sizeof(dynptr_buf), 0, &dptr);
+	bpf_probe_read_kernel_dynptr(&dptr, 0, sizeof(dynptr_buf), user_ptr);
+	return 0;
+}
+
+SEC("socket")
+__success
+__caps_unpriv(CAP_BPF)
+__failure_unpriv
+__msg_unpriv("bpf_stream_vprintk is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
+int stream_vprintk_noperfmon(void *ctx)
+{
+	bpf_stream_printk(BPF_STDOUT, "%pB", (void *)kaddr);
+	return 0;
+}
+
+SEC("socket")
+__success
+__caps_unpriv(CAP_BPF)
+__failure_unpriv
+__msg_unpriv("bpf_get_kmem_cache is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
+int get_kmem_cache_noperfmon(void *ctx)
+{
+	return !!bpf_get_kmem_cache(kaddr);
+}
+
+__weak int subprog_untrusted_read(void *p __arg_untrusted)
+{
+	return *(char *)p;
+}
+
+SEC("socket")
+__success
+__caps_unpriv(CAP_BPF)
+__failure_unpriv
+__msg_unpriv("rdonly_untrusted_mem access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN")
+int arg_untrusted_read_noperfmon(void *ctx)
+{
+	return subprog_untrusted_read(0);
+}
+
+char _license[] SEC("license") = "GPL";