From dfeb376dd4cb2c5004aeb625e2475f58a5ff2ea7 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Mon, 18 May 2020 22:38:24 -0700 Subject: 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 Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Reviewed-by: Jann Horn Link: https://lore.kernel.org/bpf/20200519053824.1089415-1-andriin@fb.com --- tools/testing/selftests/bpf/progs/test_mmap.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'tools/testing/selftests/bpf/progs/test_mmap.c') 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 @@ -7,6 +7,14 @@ 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 */ -- cgit v1.2.3