From: Kumar Kartikeya Dwivedi memxor@gmail.com
mainline inclusion from mainline-v6.13-rc3 commit 838a10bd2ebfe11a60dd67687533a7cfc220cc86 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBEDPP CVE: CVE-2024-56702
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Arguments to a raw tracepoint are tagged as trusted, which carries the semantics that the pointer will be non-NULL. However, in certain cases, a raw tracepoint argument may end up being NULL. More context about this issue is available in [0].
Thus, there is a discrepancy between the reality, that raw_tp arguments can actually be NULL, and the verifier's knowledge, that they are never NULL, causing explicit NULL check branch to be dead code eliminated.
A previous attempt [1], i.e. the second fixed commit, was made to simulate symbolic execution as if in most accesses, the argument is a non-NULL raw_tp, except for conditional jumps. This tried to suppress branch prediction while preserving compatibility, but surfaced issues with production programs that were difficult to solve without increasing verifier complexity. A more complete discussion of issues and fixes is available at [2].
Fix this by maintaining an explicit list of tracepoints where the arguments are known to be NULL, and mark the positional arguments as PTR_MAYBE_NULL. Additionally, capture the tracepoints where arguments are known to be ERR_PTR, and mark these arguments as scalar values to prevent potential dereference.
Each hex digit is used to encode NULL-ness (0x1) or ERR_PTR-ness (0x2), shifted by the zero-indexed argument number x 4. This can be represented as follows: 1st arg: 0x1 2nd arg: 0x10 3rd arg: 0x100 ... and so on (likewise for ERR_PTR case).
In the future, an automated pass will be used to produce such a list, or insert __nullable annotations automatically for tracepoints. Each compilation unit will be analyzed and results will be collated to find whether a tracepoint pointer is definitely not null, maybe null, or an unknown state where verifier conservatively marks it PTR_MAYBE_NULL. A proof of concept of this tool from Eduard is available at [3].
Note that in case we don't find a specification in the raw_tp_null_args array and the tracepoint belongs to a kernel module, we will conservatively mark the arguments as PTR_MAYBE_NULL. This is because unlike for in-tree modules, out-of-tree module tracepoints may pass NULL freely to the tracepoint. We don't protect against such tracepoints passing ERR_PTR (which is uncommon anyway), lest we mark all such arguments as SCALAR_VALUE.
While we are it, let's adjust the test raw_tp_null to not perform dereference of the skb->mark, as that won't be allowed anymore, and make it more robust by using inline assembly to test the dead code elimination behavior, which should still stay the same.
[0]: https://lore.kernel.org/bpf/ZrCZS6nisraEqehw@jlelli-thinkpadt14gen4.remote.c... [1]: https://lore.kernel.org/all/20241104171959.2938862-1-memxor@gmail.com [2]: https://lore.kernel.org/bpf/20241206161053.809580-1-memxor@gmail.com [3]: https://github.com/eddyz87/llvm-project/tree/nullness-for-tracepoint-params
Reported-by: Juri Lelli juri.lelli@redhat.com # original bug Reported-by: Manu Bretelle chantra@meta.com # bugs in masking fix Fixes: 3f00c5239344 ("bpf: Allow trusted pointers to be passed to KF_TRUSTED_ARGS kfuncs") Fixes: cb4158ce8ec8 ("bpf: Mark raw_tp arguments with PTR_MAYBE_NULL") Reviewed-by: Eduard Zingerman eddyz87@gmail.com Co-developed-by: Jiri Olsa jolsa@kernel.org Signed-off-by: Jiri Olsa jolsa@kernel.org Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Link: https://lore.kernel.org/r/20241213221929.3495062-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Conflicts: kernel/bpf/btf.c tools/testing/selftests/bpf/progs/raw_tp_null.c [The conflicts were due to not merge commit d798ce3f4cab] Signed-off-by: Pu Lehui pulehui@huawei.com --- kernel/bpf/btf.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 138 insertions(+)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 7a82194ad51d..4299fb5b8d52 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5924,6 +5924,101 @@ static bool prog_args_trusted(const struct bpf_prog *prog) } }
+struct bpf_raw_tp_null_args { + const char *func; + u64 mask; +}; + +static const struct bpf_raw_tp_null_args raw_tp_null_args[] = { + /* sched */ + { "sched_pi_setprio", 0x10 }, + /* ... from sched_numa_pair_template event class */ + { "sched_stick_numa", 0x100 }, + { "sched_swap_numa", 0x100 }, + /* afs */ + { "afs_make_fs_call", 0x10 }, + { "afs_make_fs_calli", 0x10 }, + { "afs_make_fs_call1", 0x10 }, + { "afs_make_fs_call2", 0x10 }, + { "afs_protocol_error", 0x1 }, + { "afs_flock_ev", 0x10 }, + /* cachefiles */ + { "cachefiles_lookup", 0x1 | 0x200 }, + { "cachefiles_unlink", 0x1 }, + { "cachefiles_rename", 0x1 }, + { "cachefiles_prep_read", 0x1 }, + { "cachefiles_mark_active", 0x1 }, + { "cachefiles_mark_failed", 0x1 }, + { "cachefiles_mark_inactive", 0x1 }, + { "cachefiles_vfs_error", 0x1 }, + { "cachefiles_io_error", 0x1 }, + { "cachefiles_ondemand_open", 0x1 }, + { "cachefiles_ondemand_copen", 0x1 }, + { "cachefiles_ondemand_close", 0x1 }, + { "cachefiles_ondemand_read", 0x1 }, + { "cachefiles_ondemand_cread", 0x1 }, + { "cachefiles_ondemand_fd_write", 0x1 }, + { "cachefiles_ondemand_fd_release", 0x1 }, + /* ext4, from ext4__mballoc event class */ + { "ext4_mballoc_discard", 0x10 }, + { "ext4_mballoc_free", 0x10 }, + /* fib */ + { "fib_table_lookup", 0x100 }, + /* filelock */ + /* ... from filelock_lock event class */ + { "posix_lock_inode", 0x10 }, + { "fcntl_setlk", 0x10 }, + { "locks_remove_posix", 0x10 }, + { "flock_lock_inode", 0x10 }, + /* ... from filelock_lease event class */ + { "break_lease_noblock", 0x10 }, + { "break_lease_block", 0x10 }, + { "break_lease_unblock", 0x10 }, + { "generic_delete_lease", 0x10 }, + { "time_out_leases", 0x10 }, + /* host1x */ + { "host1x_cdma_push_gather", 0x10000 }, + /* huge_memory */ + { "mm_khugepaged_scan_pmd", 0x10 }, + { "mm_collapse_huge_page_isolate", 0x1 }, + { "mm_khugepaged_scan_file", 0x10 }, + { "mm_khugepaged_collapse_file", 0x10 }, + /* kmem */ + { "mm_page_alloc", 0x1 }, + { "mm_page_pcpu_drain", 0x1 }, + /* .. from mm_page event class */ + { "mm_page_alloc_zone_locked", 0x1 }, + /* netfs */ + { "netfs_failure", 0x10 }, + /* power */ + { "device_pm_callback_start", 0x10 }, + /* qdisc */ + { "qdisc_dequeue", 0x1000 }, + /* rxrpc */ + { "rxrpc_recvdata", 0x1 }, + { "rxrpc_resend", 0x10 }, + /* sunrpc */ + { "xs_stream_read_data", 0x1 }, + /* ... from xprt_cong_event event class */ + { "xprt_reserve_cong", 0x10 }, + { "xprt_release_cong", 0x10 }, + { "xprt_get_cong", 0x10 }, + { "xprt_put_cong", 0x10 }, + /* tcp */ + { "tcp_send_reset", 0x11 }, + /* tegra_apb_dma */ + { "tegra_dma_tx_status", 0x100 }, + /* timer_migration */ + { "tmigr_update_events", 0x1 }, + /* writeback, from writeback_folio_template event class */ + { "writeback_dirty_folio", 0x10 }, + { "folio_wait_writeback", 0x10 }, + /* rdma */ + { "mr_integ_alloc", 0x2000 }, + /* bpf_testmod */ + { "bpf_testmod_test_read", 0x0 }, +}; + bool btf_ctx_access(int off, int size, enum bpf_access_type type, const struct bpf_prog *prog, struct bpf_insn_access_aux *info) @@ -5934,6 +6029,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, const char *tname = prog->aux->attach_func_name; struct bpf_verifier_log *log = info->log; const struct btf_param *args; + bool ptr_err_raw_tp = false; const char *tag_value; u32 nr_args, arg; int i, ret; @@ -6076,6 +6172,39 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, if (prog_args_trusted(prog)) info->reg_type |= PTR_TRUSTED;
+ if (prog->expected_attach_type == BPF_TRACE_RAW_TP) { + struct btf *btf = prog->aux->attach_btf; + const struct btf_type *t; + const char *tname; + + /* BTF lookups cannot fail, return false on error */ + t = btf_type_by_id(btf, prog->aux->attach_btf_id); + if (!t) + return false; + tname = btf_name_by_offset(btf, t->name_off); + if (!tname) + return false; + /* Checked by bpf_check_attach_target */ + tname += sizeof("btf_trace_") - 1; + for (i = 0; i < ARRAY_SIZE(raw_tp_null_args); i++) { + /* Is this a func with potential NULL args? */ + if (strcmp(tname, raw_tp_null_args[i].func)) + continue; + if (raw_tp_null_args[i].mask & (0x1 << (arg * 4))) + info->reg_type |= PTR_MAYBE_NULL; + /* Is the current arg IS_ERR? */ + if (raw_tp_null_args[i].mask & (0x2 << (arg * 4))) + ptr_err_raw_tp = true; + break; + } + /* If we don't know NULL-ness specification and the tracepoint + * is coming from a loadable module, be conservative and mark + * argument as PTR_MAYBE_NULL. + */ + if (i == ARRAY_SIZE(raw_tp_null_args) && btf_is_module(btf)) + info->reg_type |= PTR_MAYBE_NULL; + } + if (tgt_prog) { enum bpf_prog_type tgt_type;
@@ -6120,6 +6249,15 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, bpf_log(log, "func '%s' arg%d has btf_id %d type %s '%s'\n", tname, arg, info->btf_id, btf_type_str(t), __btf_name_by_offset(btf, t->name_off)); + + /* Perform all checks on the validity of type for this argument, but if + * we know it can be IS_ERR at runtime, scrub pointer type and mark as + * scalar. + */ + if (ptr_err_raw_tp) { + bpf_log(log, "marking pointer arg%d as scalar as it may encode error", arg); + info->reg_type = SCALAR_VALUE; + } return true; }