From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755735AbcIUDIL (ORCPT ); Tue, 20 Sep 2016 23:08:11 -0400 Received: from mail-yw0-f176.google.com ([209.85.161.176]:35199 "EHLO mail-yw0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754649AbcIUDIK (ORCPT ); Tue, 20 Sep 2016 23:08:10 -0400 Subject: Re: [PATCH] mm: usercopy: Check for module addresses To: Kees Cook References: <1474386996-16049-1-git-send-email-labbott@redhat.com> Cc: Linux-MM , LKML , "kernel-hardening@lists.openwall.com" From: Laura Abbott Message-ID: Date: Tue, 20 Sep 2016 20:08:06 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/20/2016 04:01 PM, Kees Cook wrote: > On Tue, Sep 20, 2016 at 8:56 AM, Laura Abbott wrote: >> While running a compile on arm64, I hit a memory exposure >> >> usercopy: kernel memory exposure attempt detected from fffffc0000f3b1a8 (buffer_head) (1 bytes) >> ------------[ cut here ]------------ >> kernel BUG at mm/usercopy.c:75! >> Internal error: Oops - BUG: 0 [#1] SMP >> Modules linked in: ip6t_rpfilter ip6t_REJECT >> nf_reject_ipv6 xt_conntrack ip_set nfnetlink ebtable_broute bridge stp >> llc ebtable_nat ip6table_security ip6table_raw ip6table_nat >> nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle >> iptable_security iptable_raw iptable_nat nf_conntrack_ipv4 >> nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle >> ebtable_filter ebtables ip6table_filter ip6_tables vfat fat xgene_edac >> xgene_enet edac_core i2c_xgene_slimpro i2c_core at803x realtek xgene_dma >> mdio_xgene gpio_dwapb gpio_xgene_sb xgene_rng mailbox_xgene_slimpro nfsd >> auth_rpcgss nfs_acl lockd grace sunrpc xfs libcrc32c sdhci_of_arasan >> sdhci_pltfm sdhci mmc_core xhci_plat_hcd gpio_keys >> CPU: 0 PID: 19744 Comm: updatedb Tainted: G W 4.8.0-rc3-threadinfo+ #1 >> Hardware name: AppliedMicro X-Gene Mustang Board/X-Gene Mustang Board, BIOS 3.06.12 Aug 12 2016 >> task: fffffe03df944c00 task.stack: fffffe00d128c000 >> PC is at __check_object_size+0x70/0x3f0 >> LR is at __check_object_size+0x70/0x3f0 >> ... >> [] __check_object_size+0x70/0x3f0 >> [] filldir64+0x158/0x1a0 >> [] __fat_readdir+0x4a0/0x558 [fat] >> [] fat_readdir+0x34/0x40 [fat] >> [] iterate_dir+0x190/0x1e0 >> [] SyS_getdents64+0x88/0x120 >> [] el0_svc_naked+0x24/0x28 >> >> fffffc0000f3b1a8 is a module address. Modules may have compiled in >> strings which could get copied to userspace. In this instance, it >> looks like "." which matches with a size of 1 byte. Extend the >> is_vmalloc_addr check to be is_vmalloc_or_module_addr to cover >> all possible cases. >> >> Signed-off-by: Laura Abbott >> --- >> Longer term, it would be good to expand the check for to regions like >> regular kernel memory. >> --- >> mm/usercopy.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/mm/usercopy.c b/mm/usercopy.c >> index 8ebae91..d8b5bd3 100644 >> --- a/mm/usercopy.c >> +++ b/mm/usercopy.c >> @@ -145,8 +145,11 @@ static inline const char *check_heap_object(const void *ptr, unsigned long n, >> * Some architectures (arm64) return true for virt_addr_valid() on >> * vmalloced addresses. Work around this by checking for vmalloc >> * first. >> + * >> + * We also need to check for module addresses explicitly since we >> + * may copy static data from modules to userspace >> */ >> - if (is_vmalloc_addr(ptr)) >> + if (is_vmalloc_or_module_addr(ptr)) >> return NULL; > > I still don't understand why this happens on arm64 and not x86. > (Really what I don't understand is what virt_addr_valid() is actually > checking -- they seem to be checking very different things between x86 > and arm64.) virt_addr_valid is supposed to return true if and only if virt_to_page returns a valid pointer. arm64 is currently returning true in some cases it shouldn't. I finally got to work on a patch to fix it up so hopefully once that gets submitted we can drop these extra checks. > > Regardless, I'll get this pushed to Linus and try to make the -rc8 cut. > > Thanks! > > -Kees > >> >> if (!virt_addr_valid(ptr)) >> -- >> 2.7.4 >> > > >