From 998dd597095cbb6edd2f29020630678674181dbd Mon Sep 17 00:00:00 2001 From: Leon Hwang Date: Sun, 2 Jun 2024 18:23:58 +0800 Subject: [PATCH 1/2] bpf: Fix updating attached freplace to PROG_ARRAY map Since commit 1c123c567fb138eb ("bpf: Resolve fext program type when checking map compatibility"), freplace prog can be used as tail-callee. However, when freplace prog has been attached and then updates to PROG_ARRAY map, it will panic, because the updating checks prog type of freplace prog and 'prog->aux->dst_prog' of freplace prog is NULL. [309049.036402] BUG: kernel NULL pointer dereference, address: 0000000000000004 [309049.036419] #PF: supervisor read access in kernel mode [309049.036426] #PF: error_code(0x0000) - not-present page [309049.036432] PGD 0 P4D 0 [309049.036437] Oops: 0000 [#1] PREEMPT SMP NOPTI [309049.036444] CPU: 2 PID: 788148 Comm: test_progs Not tainted 6.8.0-31-generic #31-Ubuntu [309049.036465] Hardware name: VMware, Inc. VMware20,1/440BX Desktop Reference Platform, BIOS VMW201.00V.21805430.B64.2305221830 05/22/2023 [309049.036477] RIP: 0010:bpf_prog_map_compatible+0x2a/0x140 [309049.036488] Code: 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 49 89 fe 41 55 41 54 53 44 8b 6e 04 48 89 f3 41 83 fd 1c 75 0c 48 8b 46 38 48 8b 40 70 <44> 8b 68 04 f6 43 03 01 75 1c 48 8b 43 38 44 0f b6 a0 89 00 00 00 [309049.036505] RSP: 0018:ffffb2e080fd7ce0 EFLAGS: 00010246 [309049.036513] RAX: 0000000000000000 RBX: ffffb2e0807c1000 RCX: 0000000000000000 [309049.036521] RDX: 0000000000000000 RSI: ffffb2e0807c1000 RDI: ffff990290259e00 [309049.036528] RBP: ffffb2e080fd7d08 R08: 0000000000000000 R09: 0000000000000000 [309049.036536] R10: 0000000000000000 R11: 0000000000000000 R12: ffff990290259e00 [309049.036543] R13: 000000000000001c R14: ffff990290259e00 R15: ffff99028e29c400 [309049.036551] FS: 00007b82cbc28140(0000) GS:ffff9903b3f00000(0000) knlGS:0000000000000000 [309049.036559] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [309049.036566] CR2: 0000000000000004 CR3: 0000000101286002 CR4: 00000000003706f0 [309049.036573] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [309049.036581] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [309049.036588] Call Trace: [309049.036592] [309049.036597] ? show_regs+0x6d/0x80 [309049.036604] ? __die+0x24/0x80 [309049.036619] ? page_fault_oops+0x99/0x1b0 [309049.036628] ? do_user_addr_fault+0x2ee/0x6b0 [309049.036634] ? exc_page_fault+0x83/0x1b0 [309049.036641] ? asm_exc_page_fault+0x27/0x30 [309049.036649] ? bpf_prog_map_compatible+0x2a/0x140 [309049.036656] prog_fd_array_get_ptr+0x2c/0x70 [309049.036664] bpf_fd_array_map_update_elem+0x37/0x130 [309049.036671] bpf_map_update_value+0x1d3/0x260 [309049.036677] map_update_elem+0x1fa/0x360 [309049.036683] __sys_bpf+0x54c/0xa10 [309049.036689] __x64_sys_bpf+0x1a/0x30 [309049.036694] x64_sys_call+0x1936/0x25c0 [309049.036700] do_syscall_64+0x7f/0x180 [309049.036706] ? do_syscall_64+0x8c/0x180 [309049.036712] ? do_syscall_64+0x8c/0x180 [309049.036717] ? irqentry_exit+0x43/0x50 [309049.036723] ? common_interrupt+0x54/0xb0 [309049.036729] entry_SYSCALL_64_after_hwframe+0x73/0x7b Why 'prog->aux->dst_prog' of freplace prog is NULL? It causes by commit 3aac1ead5eb6b76f ("bpf: Move prog->aux->linked_prog and trampoline into bpf_link on attach"). As 'prog->aux->dst_prog' of freplace prog is set as NULL when attach, freplace prog does not have stable prog type. But when to update freplace prog to PROG_ARRAY map, it requires checking prog type. They are conflict in theory. This patch is unable to resolve this issue thoroughly. It resolves prog type of freplace prog by 'prog->aux->saved_dst_prog_type' to avoid panic. Signed-off-by: Leon Hwang --- include/linux/bpf_verifier.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 50aa87f8d77ff..b648a96ca310b 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -845,7 +845,7 @@ static inline u32 type_flag(u32 type) static inline enum bpf_prog_type resolve_prog_type(const struct bpf_prog *prog) { return prog->type == BPF_PROG_TYPE_EXT ? - prog->aux->dst_prog->type : prog->type; + prog->aux->saved_dst_prog_type : prog->type; } static inline bool bpf_prog_check_recur(const struct bpf_prog *prog) From dd5fe62bcaf8b20e7a98863ad0c3e14510bf3f4f Mon Sep 17 00:00:00 2001 From: Leon Hwang Date: Sun, 2 Jun 2024 18:45:05 +0800 Subject: [PATCH 2/2] selftests/bpf: Add testcase for updating attached freplace prog to PROG_ARRAY map Add a selftest to confirm the issue, panic when update attached freplace prog to PROG_ARRAY map, has been fixed. cd tools/testing/selftests/bpf; ./test_progs -t tailcall 324/18 tailcalls/tailcall_freplace:OK 324 tailcalls:OK Summary: 1/18 PASSED, 0 SKIPPED, 0 FAILED Signed-off-by: Leon Hwang --- .../selftests/bpf/prog_tests/tailcalls.c | 82 +++++++++++++++++++ .../selftests/bpf/progs/tailcall_freplace.c | 34 ++++++++ .../testing/selftests/bpf/progs/tc_bpf2bpf.c | 21 +++++ 3 files changed, 137 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/tailcall_freplace.c create mode 100644 tools/testing/selftests/bpf/progs/tc_bpf2bpf.c diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c index 59993fc9c0d7e..d0c6f0d2a4233 100644 --- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c +++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c @@ -3,6 +3,8 @@ #include #include #include "tailcall_poke.skel.h" +#include "tailcall_freplace.skel.h" +#include "tc_bpf2bpf.skel.h" /* test_tailcall_1 checks basic functionality by patching multiple locations @@ -1187,6 +1189,84 @@ static void test_tailcall_poke(void) tailcall_poke__destroy(call); } +static void test_tailcall_freplace(void) +{ + struct tailcall_freplace *skel = NULL; + struct tc_bpf2bpf *tgt_skel = NULL; + struct bpf_link *freplace = NULL; + struct bpf_map *data_map; + int prog_fd, data_fd; + char buff[128] = {}; + __u32 key = 0; + int err, val; + + LIBBPF_OPTS(bpf_test_run_opts, topts, + .data_in = buff, + .data_size_in = sizeof(buff), + .repeat = 1, + ); + + skel = tailcall_freplace__open(); + if (!ASSERT_OK_PTR(skel, "open skel")) + goto out; + + tgt_skel = tc_bpf2bpf__open_and_load(); + if (!ASSERT_OK_PTR(tgt_skel, "open tgt_skel")) + goto out; + + err = bpf_program__set_attach_target(skel->progs.entry, + bpf_program__fd(tgt_skel->progs.entry), + "subprog"); + if (!ASSERT_OK(err, "set_attach_target")) + goto out; + + err = tailcall_freplace__load(skel); + if (!ASSERT_OK(err, "load skel")) + goto out; + + freplace = bpf_program__attach_freplace(skel->progs.entry, + bpf_program__fd(tgt_skel->progs.entry), + "subprog"); + if (!ASSERT_OK_PTR(freplace, "attatch_freplace")) + goto out; + + prog_fd = bpf_program__fd(skel->progs.entry); + if (!ASSERT_GE(prog_fd, 0, "prog_fd")) + goto out; + + err = bpf_map_update_elem(bpf_map__fd(skel->maps.jmp_table), &key, + &prog_fd, BPF_ANY); + if (!ASSERT_OK(err, "update jmp_table")) + goto out; + + prog_fd = bpf_program__fd(tgt_skel->progs.entry); + if (!ASSERT_GE(prog_fd, 0, "prog_fd")) + goto out; + + err = bpf_prog_test_run_opts(prog_fd, &topts); + ASSERT_OK(err, "test_run"); + ASSERT_EQ(topts.retval, 1, "test_run retval"); + + data_map = bpf_object__find_map_by_name(skel->obj, ".bss"); + if (!ASSERT_FALSE(!data_map || !bpf_map__is_internal(data_map), + "find .bss map")) + goto out; + + data_fd = bpf_map__fd(data_map); + if (!ASSERT_GE(data_fd, 0, ".bss map_fd")) + goto out; + + key = 0; + err = bpf_map_lookup_elem(data_fd, &key, &val); + ASSERT_OK(err, "tailcall count"); + ASSERT_EQ(val, 34, "tailcall count"); + +out: + bpf_link__destroy(freplace); + tc_bpf2bpf__destroy(tgt_skel); + tailcall_freplace__destroy(skel); +} + void test_tailcalls(void) { if (test__start_subtest("tailcall_1")) @@ -1223,4 +1303,6 @@ void test_tailcalls(void) test_tailcall_bpf2bpf_fentry_entry(); if (test__start_subtest("tailcall_poke")) test_tailcall_poke(); + if (test__start_subtest("tailcall_freplace")) + test_tailcall_freplace(); } diff --git a/tools/testing/selftests/bpf/progs/tailcall_freplace.c b/tools/testing/selftests/bpf/progs/tailcall_freplace.c new file mode 100644 index 0000000000000..fe25343e9d2fa --- /dev/null +++ b/tools/testing/selftests/bpf/progs/tailcall_freplace.c @@ -0,0 +1,34 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include "bpf_legacy.h" + +struct { + __uint(type, BPF_MAP_TYPE_PROG_ARRAY); + __uint(max_entries, 1); + __uint(key_size, sizeof(__u32)); + __uint(value_size, sizeof(__u32)); +} jmp_table SEC(".maps"); + +int count = 0; + +__noinline int +subprog(struct __sk_buff *skb) +{ + volatile int ret = 1; + + count++; + + bpf_tail_call_static(skb, &jmp_table, 0); + + return ret; +} + +SEC("freplace") +int entry(struct __sk_buff *skb) +{ + return subprog(skb); +} + +char __license[] SEC("license") = "GPL"; diff --git a/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c b/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c new file mode 100644 index 0000000000000..54abda6c3246e --- /dev/null +++ b/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c @@ -0,0 +1,21 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include "bpf_legacy.h" + +__noinline int +subprog(struct __sk_buff *skb) +{ + volatile int ret = 1; + + return ret; +} + +SEC("tc") +int entry(struct __sk_buff *skb) +{ + return subprog(skb); +} + +char __license[] SEC("license") = "GPL";