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From: Andy Lutomirski <luto@kernel.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	linux-doc@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
	linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. J. Lu" <hjl.tools@gmail.com>,
	"Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>, Oleg Nesterov <oleg@redhat.com>,
	Arnd Bergmann <arnd@arndb.de>,
	mike.kravetz@oracle.com
Subject: Re: [PATCH 05/10] x86/cet: ELF header parsing of Control Flow Enforcement
Date: Thu, 7 Jun 2018 11:38:02 -0700	[thread overview]
Message-ID: <CALCETrVyGdWnU1B5vZK4QP2TGVjTCg5wsPX8iAQRGzpcGNGr5g@mail.gmail.com> (raw)
In-Reply-To: <20180607143807.3611-6-yu-cheng.yu@intel.com>

On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> Look in .note.gnu.property of an ELF file and check if shadow stack needs
> to be enabled for the task.

Nice!  But please structure it so it's one function that parses out
all the ELF notes and some other code (a table or a switch statement)
that handles them.  We will probably want to add more kernel-parsed
ELF notes some day, so let's structure the code to make it easier.

> +static int find_cet(u8 *buf, u32 size, u32 align, int *shstk, int *ibt)
> +{
> +       unsigned long start = (unsigned long)buf;
> +       struct elf_note *note = (struct elf_note *)buf;
> +
> +       *shstk = 0;
> +       *ibt = 0;
> +
> +       /*
> +        * Go through the x86_note_gnu_property array pointed by
> +        * buf and look for shadow stack and indirect branch
> +        * tracking features.
> +        * The GNU_PROPERTY_X86_FEATURE_1_AND entry contains only
> +        * one u32 as data.  Do not go beyond buf_size.
> +        */
> +
> +       while ((unsigned long) (note + 1) - start < size) {
> +               /* Find the NT_GNU_PROPERTY_TYPE_0 note. */
> +               if (note->n_namesz == 4 &&
> +                   note->n_type == NT_GNU_PROPERTY_TYPE_0 &&
> +                   memcmp(note + 1, "GNU", 4) == 0) {
> +                       u8 *ptr, *ptr_end;
> +
> +                       /* Check for invalid property. */
> +                       if (note->n_descsz < 8 ||
> +                          (note->n_descsz % align) != 0)
> +                               return 0;
> +
> +                       /* Start and end of property array. */
> +                       ptr = (u8 *)(note + 1) + 4;
> +                       ptr_end = ptr + note->n_descsz;

Exploitable bug here?  You haven't checked that ptr is in bounds or
that ptr + ptr_end is in bounds (or that ptr_end > ptr, for that
matter).

> +
> +                       while (1) {
> +                               u32 type = *(u32 *)ptr;
> +                               u32 datasz = *(u32 *)(ptr + 4);
> +
> +                               ptr += 8;
> +                               if ((ptr + datasz) > ptr_end)
> +                                       break;
> +
> +                               if (type == GNU_PROPERTY_X86_FEATURE_1_AND &&
> +                                   datasz == 4) {
> +                                       u32 p = *(u32 *)ptr;
> +
> +                                       if (p & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
> +                                               *shstk = 1;
> +                                       if (p & GNU_PROPERTY_X86_FEATURE_1_IBT)
> +                                               *ibt = 1;
> +                                       return 1;
> +                               }
> +                       }
> +               }
> +
> +               /*
> +                * Note sections like .note.ABI-tag and .note.gnu.build-id
> +                * are aligned to 4 bytes in 64-bit ELF objects.
> +                */
> +               note = (void *)note + ELF_NOTE_NEXT_OFFSET(note, align);

A malicious value here will probably just break out of the while
statement, but it's still scary.

> +       }
> +
> +       return 0;
> +}
> +
> +static int check_pt_note_segment(struct file *file,
> +                                unsigned long note_size, loff_t *pos,
> +                                u32 align, int *shstk, int *ibt)
> +{
> +       int retval;
> +       char *note_buf;
> +
> +       /*
> +        * Try to read in the whole PT_NOTE segment.
> +        */
> +       note_buf = kmalloc(note_size, GFP_KERNEL);

kmalloc() with fully user-controlled, unchecked size is not a good idea.

  reply	other threads:[~2018-06-07 18:38 UTC|newest]

Thread overview: 98+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-07 14:37 [PATCH 00/10] Control Flow Enforcement - Part (3) Yu-cheng Yu
2018-06-07 14:37 ` [PATCH 01/10] x86/cet: User-mode shadow stack support Yu-cheng Yu
2018-06-07 16:37   ` Andy Lutomirski
2018-06-07 17:46     ` Yu-cheng Yu
2018-06-07 17:55       ` Dave Hansen
2018-06-07 18:23       ` Andy Lutomirski
2018-06-12 11:56   ` Balbir Singh
2018-06-12 15:03     ` Yu-cheng Yu
2018-06-07 14:37 ` [PATCH 02/10] x86/cet: Introduce WRUSS instruction Yu-cheng Yu
2018-06-07 16:40   ` Andy Lutomirski
2018-06-07 16:51     ` Yu-cheng Yu
2018-06-07 18:41     ` Peter Zijlstra
2018-06-07 20:31       ` Yu-cheng Yu
2018-06-11  8:17     ` Peter Zijlstra
2018-06-11 15:02       ` Yu-cheng Yu
2018-06-14  1:30   ` Balbir Singh
2018-06-14 14:43     ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 03/10] x86/cet: Signal handling for shadow stack Yu-cheng Yu
2018-06-07 18:30   ` Andy Lutomirski
2018-06-07 18:58     ` Florian Weimer
2018-06-07 19:51       ` Yu-cheng Yu
2018-06-07 20:07     ` Cyrill Gorcunov
2018-06-07 20:57       ` Andy Lutomirski
2018-06-08 12:07         ` Cyrill Gorcunov
2018-06-07 20:12     ` Yu-cheng Yu
2018-06-07 20:17       ` Dave Hansen
2018-06-07 14:38 ` [PATCH 04/10] x86/cet: Handle thread " Yu-cheng Yu
2018-06-07 18:21   ` Andy Lutomirski
2018-06-07 19:47     ` Florian Weimer
2018-06-07 20:53       ` Andy Lutomirski
2018-06-08 14:53         ` Florian Weimer
2018-06-08 15:01           ` Andy Lutomirski
2018-06-08 15:50             ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 05/10] x86/cet: ELF header parsing of Control Flow Enforcement Yu-cheng Yu
2018-06-07 18:38   ` Andy Lutomirski [this message]
2018-06-07 20:40     ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 06/10] x86/cet: Add arch_prctl functions for shadow stack Yu-cheng Yu
2018-06-07 18:48   ` Andy Lutomirski
2018-06-07 20:30     ` Yu-cheng Yu
2018-06-07 21:01       ` Andy Lutomirski
2018-06-07 22:02         ` H.J. Lu
2018-06-07 23:01           ` Andy Lutomirski
2018-06-08  4:09             ` H.J. Lu
2018-06-08  4:38               ` Andy Lutomirski
2018-06-08 12:24                 ` H.J. Lu
2018-06-08 14:57                   ` Andy Lutomirski
2018-06-08 15:52                     ` Cyrill Gorcunov
2018-06-08  4:22           ` H.J. Lu
2018-06-08  4:35             ` Andy Lutomirski
2018-06-08 12:17               ` H.J. Lu
2018-06-12 10:03           ` Thomas Gleixner
2018-06-12 11:43             ` H.J. Lu
2018-06-12 16:01               ` Andy Lutomirski
2018-06-12 16:05                 ` H.J. Lu
2018-06-12 16:34                   ` Andy Lutomirski
2018-06-12 16:51                     ` H.J. Lu
2018-06-12 18:59                       ` Thomas Gleixner
2018-06-12 19:34                         ` H.J. Lu
2018-06-18 22:03                           ` Andy Lutomirski
2018-06-19  0:52                             ` Kees Cook
2018-06-19  6:40                               ` Florian Weimer
2018-06-19 14:50                               ` Andy Lutomirski
2018-06-19 16:44                                 ` Kees Cook
2018-06-19 16:59                                   ` Yu-cheng Yu
2018-06-19 17:07                                     ` Kees Cook
2018-06-19 17:20                                       ` Andy Lutomirski
2018-06-19 20:12                                         ` Kees Cook
2018-06-19 20:47                                           ` Andy Lutomirski
2018-06-19 22:38                                             ` Yu-cheng Yu
2018-06-20  0:50                                               ` Andy Lutomirski
2018-06-21 23:07                                                 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 07/10] mm: Prevent mprotect from changing " Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 08/10] mm: Prevent mremap of " Yu-cheng Yu
2018-06-07 18:48   ` Andy Lutomirski
2018-06-07 20:18     ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 09/10] mm: Prevent madvise from changing " Yu-cheng Yu
2018-06-07 20:54   ` Andy Lutomirski
2018-06-07 21:09   ` Nadav Amit
2018-06-07 21:18     ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 10/10] mm: Prevent munmap and remap_file_pages of " Yu-cheng Yu
2018-06-07 18:50   ` Andy Lutomirski
2018-06-07 20:15     ` Yu-cheng Yu
2018-06-12 10:56 ` [PATCH 00/10] Control Flow Enforcement - Part (3) Balbir Singh
2018-06-12 15:03   ` Yu-cheng Yu
2018-06-12 16:00     ` Andy Lutomirski
2018-06-12 16:21       ` Yu-cheng Yu
2018-06-12 16:31         ` Andy Lutomirski
2018-06-12 17:24           ` Yu-cheng Yu
2018-06-12 20:15             ` Yu-cheng Yu
2018-06-14  1:07     ` Balbir Singh
2018-06-14 14:56       ` Yu-cheng Yu
2018-06-17  3:16         ` Balbir Singh
2018-06-18 21:44           ` Andy Lutomirski
2018-06-19  8:52             ` Balbir Singh
2018-06-26  2:46 ` Jann Horn
2018-06-26 14:56   ` Yu-cheng Yu
2018-06-26  5:26 ` Andy Lutomirski
2018-06-26 14:56   ` Yu-cheng Yu

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