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selftests/bpf: Add tests for raw_tp null handling

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Ensure that trusted PTR_TO_BTF_ID accesses perform PROBE_MEM handling in
raw_tp program. Without the previous fix, this selftest crashes the
kernel due to a NULL-pointer dereference. Also ensure that dead code
elimination does not kick in for checks on the pointer.

Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20241104171959.2938862-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2024-11-04 09:19:59 -08:00 committed by Alexei Starovoitov
parent 0e2fb011a0
commit d798ce3f4c
4 changed files with 67 additions and 0 deletions
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8
tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
View File

@ -40,6 +40,14 @@ DECLARE_TRACE(bpf_testmod_test_nullable_bare,
TP_ARGS(ctx__nullable)
);
struct sk_buff;
DECLARE_TRACE(bpf_testmod_test_raw_tp_null,
TP_PROTO(struct sk_buff *skb),
TP_ARGS(skb)
);
#undef BPF_TESTMOD_DECLARE_TRACE
#ifdef DECLARE_TRACE_WRITABLE
#define BPF_TESTMOD_DECLARE_TRACE(call, proto, args, size) \

2
tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
View File

@ -380,6 +380,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
(void)bpf_testmod_test_arg_ptr_to_struct(&struct_arg1_2);
(void)trace_bpf_testmod_test_raw_tp_null(NULL);
struct_arg3 = kmalloc((sizeof(struct bpf_testmod_struct_arg_3) +
sizeof(int)), GFP_KERNEL);
if (struct_arg3 != NULL) {

25
tools/testing/selftests/bpf/prog_tests/raw_tp_null.c Normal file
View File

@ -0,0 +1,25 @@
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
#include <test_progs.h>
#include "raw_tp_null.skel.h"
void test_raw_tp_null(void)
{
struct raw_tp_null *skel;
skel = raw_tp_null__open_and_load();
if (!ASSERT_OK_PTR(skel, "raw_tp_null__open_and_load"))
return;
skel->bss->tid = sys_gettid();
if (!ASSERT_OK(raw_tp_null__attach(skel), "raw_tp_null__attach"))
goto end;
ASSERT_OK(trigger_module_test_read(2), "trigger testmod read");
ASSERT_EQ(skel->bss->i, 3, "invocations");
end:
raw_tp_null__destroy(skel);
}

32
tools/testing/selftests/bpf/progs/raw_tp_null.c Normal file
View File

@ -0,0 +1,32 @@
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
#include <vmlinux.h>
#include <bpf/bpf_tracing.h>
char _license[] SEC("license") = "GPL";
int tid;
int i;
SEC("tp_btf/bpf_testmod_test_raw_tp_null")
int BPF_PROG(test_raw_tp_null, struct sk_buff *skb)
{
struct task_struct *task = bpf_get_current_task_btf();
if (task->pid != tid)
return 0;
i = i + skb->mark + 1;
/* The compiler may move the NULL check before this deref, which causes
* the load to fail as deref of scalar. Prevent that by using a barrier.
*/
barrier();
/* If dead code elimination kicks in, the increment below will
* be removed. For raw_tp programs, we mark input arguments as
* PTR_MAYBE_NULL, so branch prediction should never kick in.
*/
if (!skb)
i += 2;
return 0;
}