On 09/20/2016 04:01 PM, Kees Cook wrote:
On Tue, Sep 20, 2016 at 8:56 AM, Laura Abbott <labbott@xxxxxxxxxx> 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 ... [<fffffc00082b4280>] __check_object_size+0x70/0x3f0 [<fffffc00082cdc30>] filldir64+0x158/0x1a0 [<fffffc0000f327e8>] __fat_readdir+0x4a0/0x558 [fat] [<fffffc0000f328d4>] fat_readdir+0x34/0x40 [fat] [<fffffc00082cd8f8>] iterate_dir+0x190/0x1e0 [<fffffc00082cde58>] SyS_getdents64+0x88/0x120 [<fffffc0008082c70>] 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 <labbott@xxxxxxxxxx> --- 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! -Keesif (!virt_addr_valid(ptr)) -- 2.7.4
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