From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 34EC7C4332F for ; Wed, 2 Nov 2022 04:37:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229533AbiKBEha (ORCPT ); Wed, 2 Nov 2022 00:37:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229471AbiKBEh1 (ORCPT ); Wed, 2 Nov 2022 00:37:27 -0400 Received: from mail-yw1-x112f.google.com (mail-yw1-x112f.google.com [IPv6:2607:f8b0:4864:20::112f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EDAC9ED for ; Tue, 1 Nov 2022 21:37:22 -0700 (PDT) Received: by mail-yw1-x112f.google.com with SMTP id 00721157ae682-3691e040abaso155758167b3.9 for ; Tue, 01 Nov 2022 21:37:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=kl7jVJ5y1oJ5tW7Nuyev1s6MjsKIGw83WGsKI/onrLQ=; b=Q0MGEOK+oOLZwpq9uwgU9Peye3A1IVvgxAaaw7txILYll0hfqC/5PrjNU9exdDMF3Z Dqs5Yj8pNaX5TXUV1ExT0o2U2+nMhMe9f3dhxcnYzdub/LlUgURhjm0MRIBDEe2BtIku KYyT5a3Iz+EA3j2WWL9wQcxsEj+ZPs2K3aMqA1sQwZ/Np0t+RmmSf3q74+YpQNuKjSLZ FWD8WQnxBJsvEoJsHiR72J5o7Vd+jknYYSTInuf+clvGRb4K3jn+5MBGU4ozjP2fsZf8 ZeWVaGGirdm8CWQvgu5q8ePPwr1yQmwo5Btfv5ZQr6L+HtRWRcvLtJDsPy09qvmSVvik Piig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=kl7jVJ5y1oJ5tW7Nuyev1s6MjsKIGw83WGsKI/onrLQ=; b=XU4uwN2jZlpkxAxt+m+f1mOmgNCmwah5B72g9BY189k1r31u8dW6sDZ9U8IYDAoaOo xcnv9hmWYYBnT3tJ2nSEqo/wV98ZYEjB3nAI21xJPXl2Dmii1UDYCclqi8dC21NfUjZQ 2QpJf/Kb/pu0S0fGy5VtmeKXxKa8MaK2L8R5VhR6xh0D5SO4ii2ZuvxuEBES7gBTPyDK Tw5MwMhpP8bzvqJR9TqNG7AVEkPBI/CmIOiP3JkHYkgLHhiqdOUb93VcJLooyNoSN3Tz N40JQcvIfdpbikjGAJEO8mi1VPk4dovPKEY+CutaoWgQQkW91UVlmjuuYTIIRfIyUNCf RccA== X-Gm-Message-State: ACrzQf25Mq6ryzeSgcnnn9EY3UFAhWoTgD7aZ3TIUsndlLs9soIWOMOi APe/pSrE01ztScrPf3esfQrIHAcuzscuj2CLBx/JgA== X-Google-Smtp-Source: AMsMyM6j1szn06dZj2dfYwuGMkz2Ci3yBeV/a3S/Ue5Qnj/mNeMCZVW3DJoUD3U22hGeNDj8O044zJY4Wk9rzZZtFpI= X-Received: by 2002:a81:7585:0:b0:368:28bd:9932 with SMTP id q127-20020a817585000000b0036828bd9932mr20627557ywc.332.1667363841841; Tue, 01 Nov 2022 21:37:21 -0700 (PDT) MIME-Version: 1.0 References: <20221101040440.3637007-1-zhongbaisong@huawei.com> <20221101210542.724e3442@kernel.org> <202211012121.47D68D0@keescook> In-Reply-To: <202211012121.47D68D0@keescook> From: Eric Dumazet Date: Tue, 1 Nov 2022 21:37:10 -0700 Message-ID: Subject: Re: [PATCH -next] bpf, test_run: fix alignment problem in bpf_prog_test_run_skb() To: Kees Cook Cc: Jakub Kicinski , zhongbaisong , Daniel Borkmann , davem@davemloft.net, pabeni@redhat.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org, song@kernel.org, yhs@fb.com, haoluo@google.com, Alexander Potapenko , Marco Elver , Dmitry Vyukov , Linux MM , kasan-dev@googlegroups.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 1, 2022 at 9:27 PM Kees Cook wrote: > > On Tue, Nov 01, 2022 at 09:05:42PM -0700, Jakub Kicinski wrote: > > On Wed, 2 Nov 2022 10:59:44 +0800 zhongbaisong wrote: > > > On 2022/11/2 0:45, Daniel Borkmann wrote: > > > > [ +kfence folks ] > > > > > > + cc: Alexander Potapenko, Marco Elver, Dmitry Vyukov > > > > > > Do you have any suggestions about this problem? > > > > + Kees who has been sending similar patches for drivers > > > > > > On 11/1/22 5:04 AM, Baisong Zhong wrote: > > > >> Recently, we got a syzkaller problem because of aarch64 > > > >> alignment fault if KFENCE enabled. > > > >> > > > >> When the size from user bpf program is an odd number, like > > > >> 399, 407, etc, it will cause skb shard info's alignment access, > > > >> as seen below: > > > >> > > > >> BUG: KFENCE: use-after-free read in __skb_clone+0x23c/0x2a0 > > > >> net/core/skbuff.c:1032 > > > >> > > > >> Use-after-free read at 0xffff6254fffac077 (in kfence-#213): > > > >> __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:26 [inline] > > > >> arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline] > > > >> arch_atomic_inc include/linux/atomic-arch-fallback.h:270 [inline] > > > >> atomic_inc include/asm-generic/atomic-instrumented.h:241 [inline] > > > >> __skb_clone+0x23c/0x2a0 net/core/skbuff.c:1032 > > > >> skb_clone+0xf4/0x214 net/core/skbuff.c:1481 > > > >> ____bpf_clone_redirect net/core/filter.c:2433 [inline] > > > >> bpf_clone_redirect+0x78/0x1c0 net/core/filter.c:2420 > > > >> bpf_prog_d3839dd9068ceb51+0x80/0x330 > > > >> bpf_dispatcher_nop_func include/linux/bpf.h:728 [inline] > > > >> bpf_test_run+0x3c0/0x6c0 net/bpf/test_run.c:53 > > > >> bpf_prog_test_run_skb+0x638/0xa7c net/bpf/test_run.c:594 > > > >> bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] > > > >> __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] > > > >> __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 > > > >> > > > >> kfence-#213: 0xffff6254fffac000-0xffff6254fffac196, size=407, > > > >> cache=kmalloc-512 > > > >> > > > >> allocated by task 15074 on cpu 0 at 1342.585390s: > > > >> kmalloc include/linux/slab.h:568 [inline] > > > >> kzalloc include/linux/slab.h:675 [inline] > > > >> bpf_test_init.isra.0+0xac/0x290 net/bpf/test_run.c:191 > > > >> bpf_prog_test_run_skb+0x11c/0xa7c net/bpf/test_run.c:512 > > > >> bpf_prog_test_run kernel/bpf/syscall.c:3148 [inline] > > > >> __do_sys_bpf kernel/bpf/syscall.c:4441 [inline] > > > >> __se_sys_bpf+0xad0/0x1634 kernel/bpf/syscall.c:4381 > > > >> __arm64_sys_bpf+0x50/0x60 kernel/bpf/syscall.c:4381 > > > >> > > > >> To fix the problem, we round up allocations with kmalloc_size_roundup() > > > >> so that build_skb()'s use of kize() is always alignment and no special > > > >> handling of the memory is needed by KFENCE. > > > >> > > > >> Fixes: 1cf1cae963c2 ("bpf: introduce BPF_PROG_TEST_RUN command") > > > >> Signed-off-by: Baisong Zhong > > > >> --- > > > >> net/bpf/test_run.c | 1 + > > > >> 1 file changed, 1 insertion(+) > > > >> > > > >> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > > > >> index 13d578ce2a09..058b67108873 100644 > > > >> --- a/net/bpf/test_run.c > > > >> +++ b/net/bpf/test_run.c > > > >> @@ -774,6 +774,7 @@ static void *bpf_test_init(const union bpf_attr > > > >> *kattr, u32 user_size, > > > >> if (user_size > size) > > > >> return ERR_PTR(-EMSGSIZE); > > > >> + size = kmalloc_size_roundup(size); > > > >> data = kzalloc(size + headroom + tailroom, GFP_USER); > > > > > > > > The fact that you need to do this roundup on call sites feels broken, no? > > > > Was there some discussion / consensus that now all k*alloc() call sites > > > > would need to be fixed up? Couldn't this be done transparently in k*alloc() > > > > when KFENCE is enabled? I presume there may be lots of other such occasions > > > > in the kernel where similar issue triggers, fixing up all call-sites feels > > > > like ton of churn compared to api-internal, generic fix. > > I hope I answer this in more detail here: > https://lore.kernel.org/lkml/202211010937.4631CB1B0E@keescook/ > > The problem is that ksize() should never have existed in the first > place. :P Every runtime bounds checker has tripped over it, and with > the addition of the __alloc_size attribute, I had to start ripping > ksize() out: it can't be used to pretend an allocation grew in size. > Things need to either preallocate more or go through *realloc() like > everything else. Luckily, ksize() is rare. > > FWIW, the above fix doesn't look correct to me -- I would expect this to > be: > > size_t alloc_size; > ... > alloc_size = kmalloc_size_roundup(size + headroom + tailroom); > data = kzalloc(alloc_size, GFP_USER); Making sure the struct skb_shared_info is aligned to a cache line does not need kmalloc_size_roundup(). What is needed is to adjust @size so that (@size + @headroom) is a multiple of SMP_CACHE_BYTES