From 2f968e9f4a953037f798802006ecd298c014b5b4 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Tue, 18 Oct 2022 17:28:16 -0700 Subject: [PATCH] libbpf: add non-mmapable data section selftest Add non-mmapable data section to test_skeleton selftest and make sure it really isn't mmapable by trying to mmap() it anyways. Also make sure that libbpf doesn't report BPF_F_MMAPABLE flag to users. Additional, some more manual testing was performed that this feature works as intended. Looking at created map through bpftool shows that flags passed to kernel are indeed zero: $ bpftool map show ... 1782: array name .data.non_mmapa flags 0x0 key 4B value 16B max_entries 1 memlock 4096B btf_id 1169 pids test_progs(8311) ... Checking BTF uploaded to kernel for this map shows that zero_key and zero_value are indeed marked as static, even though zero_key is actually original global (but STV_HIDDEN) variable: $ bpftool btf dump id 1169 ... [51] VAR 'zero_key' type_id=2, linkage=static [52] VAR 'zero_value' type_id=7, linkage=static ... [62] DATASEC '.data.non_mmapable' size=16 vlen=2 type_id=51 offset=0 size=4 (VAR 'zero_key') type_id=52 offset=4 size=12 (VAR 'zero_value') ... And original BTF does have zero_key marked as linkage=global: $ bpftool btf dump file test_skeleton.bpf.linked3.o ... [51] VAR 'zero_key' type_id=2, linkage=global [52] VAR 'zero_value' type_id=7, linkage=static ... [62] DATASEC '.data.non_mmapable' size=16 vlen=2 type_id=51 offset=0 size=4 (VAR 'zero_key') type_id=52 offset=4 size=12 (VAR 'zero_value') Bpftool didn't require any changes at all because it checks whether internal map is mmapable already, but just to double-check generated skeleton, we see that .data.non_mmapable neither sets mmaped pointer nor has a corresponding field in the skeleton: $ grep non_mmapable test_skeleton.skel.h struct bpf_map *data_non_mmapable; s->maps[7].name = ".data.non_mmapable"; s->maps[7].map = &obj->maps.data_non_mmapable; But .data.read_mostly has all of those things: $ grep read_mostly test_skeleton.skel.h struct bpf_map *data_read_mostly; struct test_skeleton__data_read_mostly { int read_mostly_var; } *data_read_mostly; s->maps[6].name = ".data.read_mostly"; s->maps[6].map = &obj->maps.data_read_mostly; s->maps[6].mmaped = (void **)&obj->data_read_mostly; _Static_assert(sizeof(s->data_read_mostly->read_mostly_var) == 4, "unexpected size of 'read_mostly_var'"); Acked-by: Stanislav Fomichev Acked-by: Dave Marchevsky Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20221019002816.359650-4-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- tools/testing/selftests/bpf/prog_tests/skeleton.c | 11 ++++++++++- tools/testing/selftests/bpf/progs/test_skeleton.c | 17 +++++++++++++++++ 2 files changed, 27 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/prog_tests/skeleton.c b/tools/testing/selftests/bpf/prog_tests/skeleton.c index 99dac52..bc6817a 100644 --- a/tools/testing/selftests/bpf/prog_tests/skeleton.c +++ b/tools/testing/selftests/bpf/prog_tests/skeleton.c @@ -2,6 +2,7 @@ /* Copyright (c) 2019 Facebook */ #include +#include struct s { int a; @@ -22,7 +23,8 @@ void test_skeleton(void) struct test_skeleton__kconfig *kcfg; const void *elf_bytes; size_t elf_bytes_sz = 0; - int i; + void *m; + int i, fd; skel = test_skeleton__open(); if (CHECK(!skel, "skel_open", "failed to open skeleton\n")) @@ -124,6 +126,13 @@ void test_skeleton(void) ASSERT_EQ(bss->huge_arr[ARRAY_SIZE(bss->huge_arr) - 1], 123, "huge_arr"); + fd = bpf_map__fd(skel->maps.data_non_mmapable); + m = mmap(NULL, getpagesize(), PROT_READ, MAP_SHARED, fd, 0); + if (!ASSERT_EQ(m, MAP_FAILED, "unexpected_mmap_success")) + munmap(m, getpagesize()); + + ASSERT_EQ(bpf_map__map_flags(skel->maps.data_non_mmapable), 0, "non_mmap_flags"); + elf_bytes = test_skeleton__elf_bytes(&elf_bytes_sz); ASSERT_OK_PTR(elf_bytes, "elf_bytes"); ASSERT_GE(elf_bytes_sz, 0, "elf_bytes_sz"); diff --git a/tools/testing/selftests/bpf/progs/test_skeleton.c b/tools/testing/selftests/bpf/progs/test_skeleton.c index 1a4e93f..adece9f 100644 --- a/tools/testing/selftests/bpf/progs/test_skeleton.c +++ b/tools/testing/selftests/bpf/progs/test_skeleton.c @@ -53,6 +53,20 @@ int out_mostly_var; char huge_arr[16 * 1024 * 1024]; +/* non-mmapable custom .data section */ + +struct my_value { int x, y, z; }; + +__hidden int zero_key SEC(".data.non_mmapable"); +static struct my_value zero_value SEC(".data.non_mmapable"); + +struct { + __uint(type, BPF_MAP_TYPE_ARRAY); + __type(key, int); + __type(value, struct my_value); + __uint(max_entries, 1); +} my_map SEC(".maps"); + SEC("raw_tp/sys_enter") int handler(const void *ctx) { @@ -75,6 +89,9 @@ int handler(const void *ctx) huge_arr[sizeof(huge_arr) - 1] = 123; + /* make sure zero_key and zero_value are not optimized out */ + bpf_map_update_elem(&my_map, &zero_key, &zero_value, BPF_ANY); + return 0; } -- 2.7.4