Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Andy Lutomirski <luto@amacapital.net>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
	Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function
Date: Fri, 7 Jun 2019 09:35:27 -0700
Message-ID: <76B7B1AE-3AEA-4162-B539-990EF3CCE2C2@amacapital.net> (raw)
In-Reply-To: <aa8a92ef231d512b5c9855ef416db050b5ab59a6.camel@intel.com>



> On Jun 7, 2019, at 9:23 AM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> 
>> On Fri, 2019-06-07 at 10:08 +0200, Peter Zijlstra wrote:
>>> On Thu, Jun 06, 2019 at 01:09:15PM -0700, Yu-cheng Yu wrote:
>>> Indirect Branch Tracking (IBT) provides an optional legacy code bitmap
>>> that allows execution of legacy, non-IBT compatible library by an
>>> IBT-enabled application.  When set, each bit in the bitmap indicates
>>> one page of legacy code.
>>> 
>>> The bitmap is allocated and setup from the application.
>>> +int cet_setup_ibt_bitmap(unsigned long bitmap, unsigned long size)
>>> +{
>>> +    u64 r;
>>> +
>>> +    if (!current->thread.cet.ibt_enabled)
>>> +        return -EINVAL;
>>> +
>>> +    if (!PAGE_ALIGNED(bitmap) || (size > TASK_SIZE_MAX))
>>> +        return -EINVAL;
>>> +
>>> +    current->thread.cet.ibt_bitmap_addr = bitmap;
>>> +    current->thread.cet.ibt_bitmap_size = size;
>>> +
>>> +    /*
>>> +     * Turn on IBT legacy bitmap.
>>> +     */
>>> +    modify_fpu_regs_begin();
>>> +    rdmsrl(MSR_IA32_U_CET, r);
>>> +    r |= (MSR_IA32_CET_LEG_IW_EN | bitmap);
>>> +    wrmsrl(MSR_IA32_U_CET, r);
>>> +    modify_fpu_regs_end();
>>> +
>>> +    return 0;
>>> +}
>> 
>> So you just program a random user supplied address into the hardware.
>> What happens if there's not actually anything at that address or the
>> user munmap()s the data after doing this?
> 
> This function checks the bitmap's alignment and size, and anything else is the
> app's responsibility.  What else do you think the kernel should check?
> 

One might reasonably wonder why this state is privileged in the first place and, given that, why we’re allowing it to be written like this.

Arguably we should have another prctl to lock these values (until exec) as a gardening measure.

  reply index

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-06 20:09 [PATCH v7 00/14] Control-flow Enforcement: Branch Tracking, PTRACE Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 01/14] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 02/14] x86/cet/ibt: User-mode indirect branch tracking support Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function Yu-cheng Yu
2019-06-07  8:08   ` Peter Zijlstra
2019-06-07 16:23     ` Yu-cheng Yu
2019-06-07 16:35       ` Andy Lutomirski [this message]
2019-06-07 16:39         ` Dave Hansen
2019-06-07 16:45         ` Yu-cheng Yu
2019-06-07 17:05           ` Andy Lutomirski
2019-06-07 17:43       ` Peter Zijlstra
2019-06-07 17:59         ` Dave Hansen
2019-06-07 18:29           ` Andy Lutomirski
2019-06-07 18:58             ` Dave Hansen
2019-06-07 19:56               ` Yu-cheng Yu
2019-06-07 20:40               ` Andy Lutomirski
2019-06-07 21:05                 ` Dave Hansen
2019-06-07 19:49             ` Yu-cheng Yu
2019-06-07 20:00               ` Dave Hansen
2019-06-07 20:06                 ` Yu-cheng Yu
2019-06-07 21:09                   ` Dave Hansen
2019-06-07 22:27                     ` Andy Lutomirski
2019-06-10 16:03                       ` Yu-cheng Yu
2019-06-10 16:05                     ` Yu-cheng Yu
2019-06-10 17:28                       ` Florian Weimer
2019-06-10 17:59                       ` Dave Hansen
2019-06-07 20:43               ` Andy Lutomirski
2019-06-10 15:22                 ` Yu-cheng Yu
2019-06-10 18:02                   ` Dave Hansen
2019-06-10 19:38                     ` Yu-cheng Yu
2019-06-10 19:52                       ` Dave Hansen
2019-06-10 19:55                         ` Andy Lutomirski
2019-06-10 20:27                         ` Yu-cheng Yu
2019-06-10 20:43                           ` Dave Hansen
2019-06-10 20:58                             ` Yu-cheng Yu
2019-06-10 22:02                               ` Dave Hansen
2019-06-10 22:40                                 ` Yu-cheng Yu
2019-06-10 22:59                                   ` Dave Hansen
2019-06-10 23:20                                     ` H.J. Lu
2019-06-10 23:37                                       ` Dave Hansen
2019-06-10 23:54                                     ` Andy Lutomirski
2019-06-11  0:08                                       ` Dave Hansen
2019-06-11  0:36                                         ` Andy Lutomirski
2019-06-14 15:25                                     ` Yu-cheng Yu
2019-06-14 16:13                                       ` Dave Hansen
2019-06-14 17:13                                         ` Yu-cheng Yu
2019-06-14 20:57                                           ` Dave Hansen
2019-06-14 21:34                                             ` Yu-cheng Yu
2019-06-14 22:06                                               ` Dave Hansen
2019-06-15 15:30                                                 ` Andy Lutomirski
2019-06-11  7:24                                 ` Florian Weimer
2019-06-08 20:52           ` Pavel Machek
2019-06-10 15:47             ` Yu-cheng Yu
2019-06-11 10:33               ` Pavel Machek
2019-06-07 19:03   ` Dave Hansen
2019-06-07 19:23     ` Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 04/14] x86/cet/ibt: Handle signals for IBT Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 05/14] mm/mmap: Add IBT bitmap size to address space limit check Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 06/14] x86/cet/ibt: ELF header parsing for IBT Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 07/14] x86/cet/ibt: Add arch_prctl functions " Yu-cheng Yu
2019-06-07  8:07   ` Peter Zijlstra
2019-06-06 20:09 ` [PATCH v7 08/14] x86/cet/ibt: Add ENDBR to op-code-map Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 09/14] x86/vdso: Insert endbr32/endbr64 to vDSO Yu-cheng Yu
2019-06-06 20:26   ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 10/14] x86/vdso/32: Add ENDBR32 to __kernel_vsyscall entry point Yu-cheng Yu
2019-06-06 20:25   ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 11/14] x86/vsyscall/64: Add ENDBR64 to vsyscall entry points Yu-cheng Yu
2019-06-06 20:28   ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 12/14] x86/vsyscall/64: Fixup shadow stack and branch tracking for vsyscall Yu-cheng Yu
2019-06-06 20:27   ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 13/14] x86/cet: Add PTRACE interface for CET Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 14/14] x86: Discard .note.gnu.property sections Yu-cheng Yu

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=76B7B1AE-3AEA-4162-B539-990EF3CCE2C2@amacapital.net \
    --to=luto@amacapital.net \
    --cc=Dave.Martin@arm.com \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=bsingharora@gmail.com \
    --cc=corbet@lwn.net \
    --cc=dave.hansen@linux.intel.com \
    --cc=esyr@redhat.com \
    --cc=fweimer@redhat.com \
    --cc=gorcunov@gmail.com \
    --cc=hjl.tools@gmail.com \
    --cc=hpa@zytor.com \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mike.kravetz@oracle.com \
    --cc=mingo@redhat.com \
    --cc=nadav.amit@gmail.com \
    --cc=oleg@redhat.com \
    --cc=pavel@ucw.cz \
    --cc=peterz@infradead.org \
    --cc=ravi.v.shankar@intel.com \
    --cc=rdunlap@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=vedvyas.shanbhogue@intel.com \
    --cc=x86@kernel.org \
    --cc=yu-cheng.yu@intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org linux-mm@archiver.kernel.org
	public-inbox-index linux-mm


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/ public-inbox