Re: [PATCH 0/9] mm: Hardened usercopy
From: Ingo Molnar
Date: Sat Jul 09 2016 - 03:56:07 EST
* Rik van Riel <riel@xxxxxxxxxx> wrote:
> On Fri, 2016-07-08 at 19:22 -0700, Laura Abbott wrote:
> >
> > Even with the SLUB fixup I'm still seeing this blow up on my arm64
> > system. This is a
> > Fedora rawhide kernel + the patches
> >
> > [ 0.666700] usercopy: kernel memory exposure attempt detected from
> > fffffc0008b4dd58 (<kernel text>) (8 bytes)
> > [ 0.666720] CPU: 2 PID: 79 Comm: modprobe Tainted:
> > G W 4.7.0-0.rc6.git1.1.hardenedusercopy.fc25.aarch64 #1
> > [ 0.666733] Hardware name: AppliedMicro Mustang/Mustang, BIOS
> > 1.1.0 Nov 24 2015
> > [ 0.666744] Call trace:
> > [ 0.666756] [<fffffc0008088a20>] dump_backtrace+0x0/0x1e8
> > [ 0.666765] [<fffffc0008088c2c>] show_stack+0x24/0x30
> > [ 0.666775] [<fffffc0008455344>] dump_stack+0xa4/0xe0
> > [ 0.666785] [<fffffc000828d874>] __check_object_size+0x6c/0x230
> > [ 0.666795] [<fffffc00083a5748>] create_elf_tables+0x74/0x420
> > [ 0.666805] [<fffffc00082fb1f0>] load_elf_binary+0x828/0xb70
> > [ 0.666814] [<fffffc0008298b4c>] search_binary_handler+0xb4/0x240
> > [ 0.666823] [<fffffc0008299864>] do_execveat_common+0x63c/0x950
> > [ 0.666832] [<fffffc0008299bb4>] do_execve+0x3c/0x50
> > [ 0.666841] [<fffffc00080e3720>]
> > call_usermodehelper_exec_async+0xe8/0x148
> > [ 0.666850] [<fffffc0008084a80>] ret_from_fork+0x10/0x50
> >
> > This happens on every call to execve. This seems to be the first
> > copy_to_user in
> > create_elf_tables. I didn't get a chance to debug and I'm going out
> > of town
> > all of next week so all I have is the report unfortunately. config
> > attached.
>
> That's odd, this should be copying a piece of kernel data (not text)
> to userspace.
>
> from fs/binfmt_elf.c
>
> const char *k_platform = ELF_PLATFORM;
>
> ...
> size_t len = strlen(k_platform) + 1;
>
> u_platform = (elf_addr_t __user *)STACK_ALLOC(p, len);
> if (__copy_to_user(u_platform, k_platform, len))
> return -EFAULT;
>
> from arch/arm/include/asm/elf.h:
>
> #define ELF_PLATFORM_SIZE 8
> #define ELF_PLATFORM (elf_platform)
>
> extern char elf_platform[];
>
> from arch/arm/kernel/setup.c:
>
> char elf_platform[ELF_PLATFORM_SIZE];
> EXPORT_SYMBOL(elf_platform);
>
> ...
>
> snprintf(elf_platform, ELF_PLATFORM_SIZE, "%s%c",
> list->elf_name, ENDIANNESS);
>
> How does that end up in the .text section of the
> image, instead of in one of the various data sections?
>
> What kind of linker oddity is going on with ARM?
I think the crash happened on ARM64, not ARM.
Thanks,
Ingo