selftests/bpf: check bpf verifier log buffer usage works for HW offload

Make netdevsim print a message to the BPF verifier log buffer when a
program is offloaded.

Then use this message in hardware offload selftests to make sure that
using this buffer actually prints the message to the console for
eBPF hardware offload.

The message is appended after the last instruction is processed with the
verifying function from netdevsim. Output looks like the following:

    $ tc filter add dev foo ingress bpf obj sample_ret0.o \
        sec .text verbose skip_sw

    Prog section '.text' loaded (5)!
     - Type:         3
     - Instructions: 2 (0 over limit)
     - License:

    Verifier analysis:

    0: (b7) r0 = 0
    1: (95) exit
    [netdevsim] Hello from netdevsim!
    processed 2 insns, stack depth 0

"verbose" flag is required to see it in the console since netdevsim does
not throw an error after printing the message.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/netdevsim/bpf.c

@@ -23,6 +23,9 @@
 
 #include "netdevsim.h"
 
+#define pr_vlog(env, fmt, ...)	\
+	bpf_verifier_log_write(env, "[netdevsim] " fmt, ##__VA_ARGS__)
+
 struct nsim_bpf_bound_prog {
 	struct netdevsim *ns;
 	struct bpf_prog *prog;
@@ -77,6 +80,9 @@ nsim_bpf_verify_insn(struct bpf_verifier_env *env, int insn_idx, int prev_insn)
 	if (state->ns->bpf_bind_verifier_delay && !insn_idx)
 		msleep(state->ns->bpf_bind_verifier_delay);
 
+	if (insn_idx == env->prog->len - 1)
+		pr_vlog(env, "Hello from netdevsim!\n");
+
 	return 0;
 }
 

tools/testing/selftests/bpf/test_offload.py

@@ -362,8 +362,10 @@ class NetdevSim:
         return ip("link set dev %s mtu %d" % (self.dev["ifname"], mtu),
                   fail=fail)
 
-    def set_xdp(self, bpf, mode, force=False, JSON=True,
+    def set_xdp(self, bpf, mode, force=False, JSON=True, verbose=False,
                 fail=True, include_stderr=False):
+        if verbose:
+            bpf += " verbose"
         return ip("link set dev %s xdp%s %s" % (self.dev["ifname"], mode, bpf),
                   force=force, JSON=JSON,
                   fail=fail, include_stderr=include_stderr)
@@ -427,11 +429,13 @@ class NetdevSim:
                  (len(filters), expected))
         return filters
 
-    def cls_bpf_add_filter(self, bpf, da=False, skip_sw=False, skip_hw=False,
-                           fail=True, include_stderr=False):
+    def cls_bpf_add_filter(self, bpf, da=False, verbose=False, skip_sw=False,
+                           skip_hw=False, fail=True, include_stderr=False):
         params = ""
         if da:
             params += " da"
+        if verbose:
+            params += " verbose"
         if skip_sw:
             params += " skip_sw"
         if skip_hw:
@@ -520,6 +524,13 @@ def check_extack(output, reference, args):
 def check_extack_nsim(output, reference, args):
     check_extack(output, "Error: netdevsim: " + reference, args)
 
+def check_verifier_log(output, reference):
+    lines = output.split("\n")
+    for l in reversed(lines):
+        if l == reference:
+            return
+    fail(True, "Missing or incorrect message from netdevsim in verifier log")
+
 # Parse command line
 parser = argparse.ArgumentParser()
 parser.add_argument("--log", help="output verbose log to given file")
@@ -634,8 +645,10 @@ try:
     sim.wait_for_flush()
 
     start_test("Test TC offloads work...")
-    ret, _ = sim.cls_bpf_add_filter(obj, skip_sw=True, fail=False)
+    ret, _, err = sim.cls_bpf_add_filter(obj, verbose=True, skip_sw=True,
+                                         fail=False, include_stderr=True)
     fail(ret != 0, "TC filter did not load with TC offloads enabled")
+    check_verifier_log(err, "[netdevsim] Hello from netdevsim!")
 
     start_test("Test TC offload basics...")
     dfs = sim.dfs_get_bound_progs(expected=1)
@@ -744,12 +757,13 @@ try:
 
     sim.wait_for_flush()
     start_test("Test XDP offload...")
-    sim.set_xdp(obj, "offload")
+    _, _, err = sim.set_xdp(obj, "offload", verbose=True, include_stderr=True)
     ipl = sim.ip_link_show(xdp=True)
     link_xdp = ipl["xdp"]["prog"]
     progs = bpftool_prog_list(expected=1)
     prog = progs[0]
     fail(link_xdp["id"] != prog["id"], "Loaded program has wrong ID")
+    check_verifier_log(err, "[netdevsim] Hello from netdevsim!")
 
     start_test("Test XDP offload is device bound...")
     dfs = sim.dfs_get_bound_progs(expected=1)