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authorAndrii Nakryiko <andriin@fb.com>2020-05-18 22:38:24 -0700
committerAlexei Starovoitov <ast@kernel.org>2020-05-20 20:21:53 -0700
commitdfeb376dd4cb2c5004aeb625e2475f58a5ff2ea7 (patch)
tree641c6f335575c230f294743042295a404e1e3aee /tools
parent0550cfe8c2c6f8e7a4c348b6603a794576db12dd (diff)
bpf: Prevent mmap()'ing read-only maps as writable
As discussed in [0], it's dangerous to allow mapping BPF map, that's meant to be frozen and is read-only on BPF program side, because that allows user-space to actually store a writable view to the page even after it is frozen. This is exacerbated by BPF verifier making a strong assumption that contents of such frozen map will remain unchanged. To prevent this, disallow mapping BPF_F_RDONLY_PROG mmap()'able BPF maps as writable, ever. [0] https://lore.kernel.org/bpf/CAEf4BzYGWYhXdp6BJ7_=9OQPJxQpgug080MMjdSB72i9R+5c6g@mail.gmail.com/ Fixes: fc9702273e2e ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY") Suggested-by: Jann Horn <jannh@google.com> Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Jann Horn <jannh@google.com> Link: https://lore.kernel.org/bpf/20200519053824.1089415-1-andriin@fb.com
Diffstat (limited to 'tools')
-rw-r--r--tools/testing/selftests/bpf/prog_tests/mmap.c13
-rw-r--r--tools/testing/selftests/bpf/progs/test_mmap.c8
2 files changed, 20 insertions, 1 deletions
diff --git a/tools/testing/selftests/bpf/prog_tests/mmap.c b/tools/testing/selftests/bpf/prog_tests/mmap.c
index 6b9dce431d41..43d0b5578f46 100644
--- a/tools/testing/selftests/bpf/prog_tests/mmap.c
+++ b/tools/testing/selftests/bpf/prog_tests/mmap.c
@@ -19,7 +19,7 @@ void test_mmap(void)
const size_t map_sz = roundup_page(sizeof(struct map_data));
const int zero = 0, one = 1, two = 2, far = 1500;
const long page_size = sysconf(_SC_PAGE_SIZE);
- int err, duration = 0, i, data_map_fd, data_map_id, tmp_fd;
+ int err, duration = 0, i, data_map_fd, data_map_id, tmp_fd, rdmap_fd;
struct bpf_map *data_map, *bss_map;
void *bss_mmaped = NULL, *map_mmaped = NULL, *tmp1, *tmp2;
struct test_mmap__bss *bss_data;
@@ -37,6 +37,17 @@ void test_mmap(void)
data_map = skel->maps.data_map;
data_map_fd = bpf_map__fd(data_map);
+ rdmap_fd = bpf_map__fd(skel->maps.rdonly_map);
+ tmp1 = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, rdmap_fd, 0);
+ if (CHECK(tmp1 != MAP_FAILED, "rdonly_write_mmap", "unexpected success\n")) {
+ munmap(tmp1, 4096);
+ goto cleanup;
+ }
+ /* now double-check if it's mmap()'able at all */
+ tmp1 = mmap(NULL, 4096, PROT_READ, MAP_SHARED, rdmap_fd, 0);
+ if (CHECK(tmp1 == MAP_FAILED, "rdonly_read_mmap", "failed: %d\n", errno))
+ goto cleanup;
+
/* get map's ID */
memset(&map_info, 0, map_info_sz);
err = bpf_obj_get_info_by_fd(data_map_fd, &map_info, &map_info_sz);
diff --git a/tools/testing/selftests/bpf/progs/test_mmap.c b/tools/testing/selftests/bpf/progs/test_mmap.c
index 6239596cd14e..4eb42cff5fe9 100644
--- a/tools/testing/selftests/bpf/progs/test_mmap.c
+++ b/tools/testing/selftests/bpf/progs/test_mmap.c
@@ -9,6 +9,14 @@ char _license[] SEC("license") = "GPL";
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
+ __uint(max_entries, 4096);
+ __uint(map_flags, BPF_F_MMAPABLE | BPF_F_RDONLY_PROG);
+ __type(key, __u32);
+ __type(value, char);
+} rdonly_map SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 512 * 4); /* at least 4 pages of data */
__uint(map_flags, BPF_F_MMAPABLE);
__type(key, __u32);