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selftests: bpf: Add a test for mmapable vmlinux BTF

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Add a basic test for the ability to mmap /sys/kernel/btf/vmlinux.
Ensure that the data is valid BTF and that it is padded with zero.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-2-e8c941acc414@isovalent.com
This commit is contained in:
Lorenz Bauer 2025-05-20 14:01:18 +01:00 committed by Andrii Nakryiko
parent a539e2a6d5
commit 828226b69f
1 changed files with 81 additions and 0 deletions
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81
tools/testing/selftests/bpf/prog_tests/btf_sysfs.c Normal file
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// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
/* Copyright (c) 2025 Isovalent */
#include <test_progs.h>
#include <bpf/btf.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
static void test_btf_mmap_sysfs(const char *path, struct btf *base)
{
struct stat st;
__u64 btf_size, end;
void *raw_data = NULL;
int fd = -1;
long page_size;
struct btf *btf = NULL;
page_size = sysconf(_SC_PAGESIZE);
if (!ASSERT_GE(page_size, 0, "get_page_size"))
goto cleanup;
if (!ASSERT_OK(stat(path, &st), "stat_btf"))
goto cleanup;
btf_size = st.st_size;
end = (btf_size + page_size - 1) / page_size * page_size;
fd = open(path, O_RDONLY);
if (!ASSERT_GE(fd, 0, "open_btf"))
goto cleanup;
raw_data = mmap(NULL, btf_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_writable"))
goto cleanup;
raw_data = mmap(NULL, btf_size, PROT_READ, MAP_SHARED, fd, 0);
if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_shared"))
goto cleanup;
raw_data = mmap(NULL, end + 1, PROT_READ, MAP_PRIVATE, fd, 0);
if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_invalid_size"))
goto cleanup;
raw_data = mmap(NULL, end, PROT_READ, MAP_PRIVATE, fd, 0);
if (!ASSERT_OK_PTR(raw_data, "mmap_btf"))
goto cleanup;
if (!ASSERT_EQ(mprotect(raw_data, btf_size, PROT_READ | PROT_WRITE), -1,
"mprotect_writable"))
goto cleanup;
if (!ASSERT_EQ(mprotect(raw_data, btf_size, PROT_READ | PROT_EXEC), -1,
"mprotect_executable"))
goto cleanup;
/* Check padding is zeroed */
for (int i = btf_size; i < end; i++) {
if (((__u8 *)raw_data)[i] != 0) {
PRINT_FAIL("tail of BTF is not zero at page offset %d\n", i);
goto cleanup;
}
}
btf = btf__new_split(raw_data, btf_size, base);
if (!ASSERT_OK_PTR(btf, "parse_btf"))
goto cleanup;
cleanup:
btf__free(btf);
if (raw_data && raw_data != MAP_FAILED)
munmap(raw_data, btf_size);
if (fd >= 0)
close(fd);
}
void test_btf_sysfs(void)
{
test_btf_mmap_sysfs("/sys/kernel/btf/vmlinux", NULL);
}