From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Andy Lutomirski <luto@amacapital.net>
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, 07 Jun 2019 09:45:02 -0700 [thread overview]
Message-ID: <ac8827d7b516f4b58e1df20f45b94998d36c418c.camel@intel.com> (raw)
In-Reply-To: <76B7B1AE-3AEA-4162-B539-990EF3CCE2C2@amacapital.net>
On Fri, 2019-06-07 at 09:35 -0700, Andy Lutomirski wrote:
> > 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.
We can prevent the bitmap from being set more than once. I will test it.
Yu-cheng
next prev parent reply other threads:[~2019-06-07 16:53 UTC|newest]
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
2019-06-07 16:39 ` Dave Hansen
2019-06-07 16:45 ` Yu-cheng Yu [this message]
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
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