From patchwork Tue Jun 8 19:30:15 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Fastabend X-Patchwork-Id: 12308009 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D208FC4743F for ; Tue, 8 Jun 2021 19:33:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE93661001 for ; Tue, 8 Jun 2021 19:33:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238399AbhFHTfd (ORCPT ); Tue, 8 Jun 2021 15:35:33 -0400 Received: from mail-il1-f169.google.com ([209.85.166.169]:38558 "EHLO mail-il1-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238872AbhFHTdc (ORCPT ); Tue, 8 Jun 2021 15:33:32 -0400 Received: by mail-il1-f169.google.com with SMTP id d1so17846375ils.5; Tue, 08 Jun 2021 12:31:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:from:to:cc:date:message-id:in-reply-to:references :user-agent:mime-version:content-transfer-encoding; bh=AAEaQnkcEin0xfopI4B5HxP0UPGqn6HkcxHsdLoqoo8=; b=lN0ezurN19ijysdHRyRCpv7N1gqTE7BQCzDCX19YSxzhzI8ftYBH5Z3FUDAJSmGnPS TcR+D2T6YDMsJil0GI1UAEAR/F7s2v9DVMaHvcExwcqueWkqNOz8H+pwhoQLlrulpIwL BBeW8jfUfLJDfbQSGH8zbO9tlxqoMmRDvpElyqERq6pSt8GjgfSUt4Hsg9j+9U3cjXIo 2N+wyduePEsP6hcmiQZgS9swUaaRn8khoW/A0OplVwwV3ijjcMi5iHgSJAbx3gQkqOMh ghC9+9c18aVCk0JH3pgqZ/t9R4xWC6+YsE3JhA6VitBiCk02M9lF9qU1Yz7jEaNwnK0R ewcg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:from:to:cc:date:message-id:in-reply-to :references:user-agent:mime-version:content-transfer-encoding; bh=AAEaQnkcEin0xfopI4B5HxP0UPGqn6HkcxHsdLoqoo8=; b=EHr/VYVruuF7gtOP1Zc8lGDubjywAEghaiHFjzrImo35FwAn1nlOX/oZLbaEpxPc0E uZ3q2/7PAcWNiLKiG2evzM2dfq8TsRReLkky23chI042pm2PjXZhMCCoMqScXj8rhDMi 7PzYxsQO2KxwPk+b5lwNzzg2XW4N5KJKPeqdIjofbvDAllzFmCezN6w1LZKVIfqHXAPx O3diJDZZ58L1Pe71DUeipnu6TOWIWhyRrupYX7jYP7RmbjZ/H5eX9HRqYZjJkJcL2RMe LY+Y88tpdg+TbhbZxUsDUy5xVHV7PT3Youjk6fWM7+l/Q3JAoOZCJvjPp2jzJXnQ1JbJ /qmw== X-Gm-Message-State: AOAM532gFYEeJ8nThMImgbKBmIFBga9Hh/w0JxmLLKHdwjfGmmdQGiig uai4bZ/kSesSbkACBeu5dqg= X-Google-Smtp-Source: ABdhPJwyvZckIsCq+ekKEwln5K68p9lAiarvDCnEo/yZB9FN/vh/X12yRNJlGqvNQa6hN0ws0C8ZEQ== X-Received: by 2002:a92:c949:: with SMTP id i9mr14825767ilq.38.1623180627229; Tue, 08 Jun 2021 12:30:27 -0700 (PDT) Received: from [127.0.1.1] ([172.243.157.240]) by smtp.gmail.com with ESMTPSA id t15sm302258ilq.84.2021.06.08.12.30.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Jun 2021 12:30:26 -0700 (PDT) Subject: [PATCH bpf 1/2] bpf: Fix null ptr deref with mixed tail calls and subprogs From: John Fastabend To: ast@kernel.org, daniel@iogearbox.net, andriin@fb.com Cc: john.fastabend@gmail.com, netdev@vger.kernel.org, bpf@vger.kernel.org, maciej.fijalkowski@intel.com Date: Tue, 08 Jun 2021 12:30:15 -0700 Message-ID: <162318061518.323820.4329181800429686297.stgit@john-XPS-13-9370> In-Reply-To: <162318053542.323820.3719766457956848570.stgit@john-XPS-13-9370> References: <162318053542.323820.3719766457956848570.stgit@john-XPS-13-9370> User-Agent: StGit/0.23-85-g6af9 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net The sub-programs prog->aux->poke_tab[] is populated in jit_subprogs() and then used when emitting 'BPF_JMP|BPF_TAIL_CALL' insn->code from the individual JITs. The poke_tab[] to use is stored in the insn->imm by the code adding it to that array slot. The JIT then uses imm to find the right entry for an individual instruction. In the x86 bpf_jit_comp.c this is done by calling emit_bpf_tail_call_direct with the poke_tab[] of the imm value. However, we observed the below null-ptr-deref when mixing tail call programs with subprog programs. For this to happen we just need to mix bpf-2-bpf calls and tailcalls with some extra calls or instructions that would be patched later by one of the fixup routines. So whats happening? Before the fixup_call_args() -- where the jit op is done -- various code patching is done by do_misc_fixups(). This may increase the insn count, for example when we patch map_lookup_up using map_gen_lookup hook. This does two things. First, it means the instruction index, insn_idx field, of a tail call instruction will move by a 'delta'. In verifier code, struct bpf_jit_poke_descriptor desc = { .reason = BPF_POKE_REASON_TAIL_CALL, .tail_call.map = BPF_MAP_PTR(aux->map_ptr_state), .tail_call.key = bpf_map_key_immediate(aux), .insn_idx = i + delta, }; Then subprog start values subprog_info[i].start will be updated with the delta and any poke descriptor index will also be updated with the delta in adjust_poke_desc(). If we look at the adjust subprog starts though we see its only adjusted when the delta occurs before the new instructions, /* NOTE: fake 'exit' subprog should be updated as well. */ for (i = 0; i <= env->subprog_cnt; i++) { if (env->subprog_info[i].start <= off) continue; Earlier subprograms are not changed because their start values are not moved. But, adjust_poke_desc() does the offset + delta indiscriminately. The result is poke descriptors are potentially corrupted. Then in jit_subprogs() we only populate the poke_tab[] when the above insn_idx is less than the next subprogram start. From above we corrupted our insn_idx so we might incorrectly assume a poke descriptor is not used in a subprogram omitting it from the subprogram. And finally when the jit runs it does the deref of poke_tab when emitting the instruction and crashes with below. Because earlier step omitted the poke descriptor. The fix is straight forward with above context. Simply move same logic from adjust_subprog_starts() into adjust_poke_descs() and only adjust insn_idx when needed. [ 88.487438] BUG: KASAN: null-ptr-deref in do_jit+0x184a/0x3290 [ 88.487455] Write of size 8 at addr 0000000000000008 by task test_progs/5295 [ 88.487490] Call Trace: [ 88.487498] dump_stack+0x93/0xc2 [ 88.487515] kasan_report.cold+0x5f/0xd8 [ 88.487530] ? do_jit+0x184a/0x3290 [ 88.487542] do_jit+0x184a/0x3290 ... [ 88.487709] bpf_int_jit_compile+0x248/0x810 ... [ 88.487765] bpf_check+0x3718/0x5140 ... [ 88.487920] bpf_prog_load+0xa22/0xf10 CC: Maciej Fijalkowski Fixes: a748c6975dea3 ("bpf: propagate poke descriptors to subprograms") Reviewed-by: Daniel Borkmann Signed-off-by: John Fastabend Acked-by: Yonghong Song Acked-by: Maciej Fijalkowski Tested-by: Maciej Fijalkowski --- kernel/bpf/verifier.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 94ba5163d4c5..ac8373da849c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11408,7 +11408,7 @@ static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len } } -static void adjust_poke_descs(struct bpf_prog *prog, u32 len) +static void adjust_poke_descs(struct bpf_prog *prog, u32 off, u32 len) { struct bpf_jit_poke_descriptor *tab = prog->aux->poke_tab; int i, sz = prog->aux->size_poke_tab; @@ -11416,6 +11416,8 @@ static void adjust_poke_descs(struct bpf_prog *prog, u32 len) for (i = 0; i < sz; i++) { desc = &tab[i]; + if (desc->insn_idx <= off) + continue; desc->insn_idx += len - 1; } } @@ -11436,7 +11438,7 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of if (adjust_insn_aux_data(env, new_prog, off, len)) return NULL; adjust_subprog_starts(env, off, len); - adjust_poke_descs(new_prog, len); + adjust_poke_descs(new_prog, off, len); return new_prog; }