From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Andy Lutomirski <luto@kernel.org>
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 01/10] x86/cet: User-mode shadow stack support
Date: Thu, 07 Jun 2018 10:46:51 -0700 [thread overview]
Message-ID: <1528393611.4636.70.camel@2b52.sc.intel.com> (raw)
In-Reply-To: <CALCETrX4ALKbphJiZs4MXWtRFvQYD905bNAMTogbOeLh0Pp6xw@mail.gmail.com>
On Thu, 2018-06-07 at 09:37 -0700, Andy Lutomirski wrote:
> On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> >
> > This patch adds basic shadow stack enabling/disabling routines.
> > A task's shadow stack is allocated from memory with VM_SHSTK
> > flag set and read-only protection. The shadow stack is
> > allocated to a fixed size and that can be changed by the system
> > admin.
>
> How do threads work? Can a user program mremap() its shadow stack to
> make it bigger?
A pthread's shadow stack is allocated/freed by the kernel. This patch
has the supporting routines that handle both non-pthread and pthread.
In [PATCH 04/10] "Handle thread shadow stack", we allocate pthread
shadow stack in copy_thread_tls(), and free it in deactivate_mm().
If clone of a pthread fails, shadow stack is freed in
cet_disable_free_shstk() below (I will add more comments):
If (Current thread existing)
Disable and free shadow stack
If (Clone of a pthread fails)
Free the pthread shadow stack
We block mremap, mprotect, madvise, and munmap on a vma that has
VM_SHSTK (in separate patches).
> Also, did you add all the needed checks to make get_user_pages(),
> access_process_vm(), etc fail when called on the shadow stack? (Or at
> least fail if they're requesting write access and the FORCE bit isn't
> set.)
Currently if FORCE bit is set, these functions can write to shadow
stack, otherwise write access will fail. I will test it.
> > +#define SHSTK_SIZE (0x8000 * (test_thread_flag(TIF_IA32) ? 4 : 8))
>
> Please don't add more mode-dependent #defines. Also, please try to
> avoid adding any new code that looks at TIF_IA32 or similar. Uses of
> that bit are generally bugs, and the bit itself should get removed
> some day. If you need to make a guess, use in_compat_syscall() or
> similar if appropriate.
OK.
>
> > +
> > +static inline int cet_set_shstk_ptr(unsigned long addr)
> > +{
> > + u64 r;
> > +
> > + if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
> > + return -1;
> > +
> > + if ((addr >= TASK_SIZE) || (!IS_ALIGNED(addr, 4)))
> > + return -1;'
>
> TASK_SIZE_MAX, please. TASK_SIZE is weird and is usually the wrong
> thing to use.
OK.
>
> > +static unsigned long shstk_mmap(unsigned long addr, unsigned long len)
> > +{
> > + struct mm_struct *mm = current->mm;
> > + unsigned long populate;
> > +
> > + down_write(&mm->mmap_sem);
> > + addr = do_mmap(NULL, addr, len, PROT_READ,
> > + MAP_ANONYMOUS | MAP_PRIVATE, VM_SHSTK,
> > + 0, &populate, NULL);
> > + up_write(&mm->mmap_sem);
> > +
> > + if (populate)
> > + mm_populate(addr, populate);
>
> Please don't populate if do_mmap() failed.
I will fix it.
>
> > +int cet_setup_shstk(void)
> > +{
> > + unsigned long addr, size;
> > +
> > + if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
> > + return -EOPNOTSUPP;
> > +
> > + size = SHSTK_SIZE;
> > + addr = shstk_mmap(0, size);
> > +
> > + if (addr >= TASK_SIZE)
> > + return -ENOMEM;
>
> Please check the actual value that do_mmap() would return on error.
> (IS_ERR, 0, MAP_FAILED -- I don't remember.)
OK.
>
> > +
> > + cet_set_shstk_ptr(addr + size - sizeof(void *));
> > + current->thread.cet.shstk_base = addr;
> > + current->thread.cet.shstk_size = size;
> > + current->thread.cet.shstk_enabled = 1;
> > + return 0;
> > +}
> > +
> > +void cet_disable_shstk(void)
> > +{
> > + u64 r;
> > +
> > + if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
> > + return;
> > +
> > + rdmsrl(MSR_IA32_U_CET, r);
> > + r &= ~(MSR_IA32_CET_SHSTK_EN);
> > + wrmsrl(MSR_IA32_U_CET, r);
> > + wrmsrl(MSR_IA32_PL3_SSP, 0);
> > + current->thread.cet.shstk_enabled = 0;
> > +}
> > +
> > +void cet_disable_free_shstk(struct task_struct *tsk)
> > +{
> > + if (!cpu_feature_enabled(X86_FEATURE_SHSTK) ||
> > + !tsk->thread.cet.shstk_enabled)
> > + return;
> > +
> > + if (tsk == current)
> > + cet_disable_shstk();
>
> if tsk != current, then this will malfunction, right? What is it
> intended to do?
We get here when clone fails. In this condition, we don't disable the
calling task's shadow stack. I will add comments.
>
> > +
> > + /*
> > + * Free only when tsk is current or shares mm
> > + * with current but has its own shstk.
> > + */
> > + if (tsk->mm && (tsk->mm == current->mm) &&
> > + (tsk->thread.cet.shstk_base)) {
> > + vm_munmap(tsk->thread.cet.shstk_base,
> > + tsk->thread.cet.shstk_size);
> > + tsk->thread.cet.shstk_base = 0;
> > + tsk->thread.cet.shstk_size = 0;
> > + }
>
> I'm having trouble imagining why the kernel would ever want to
> automatically free the shadow stack vma. What is this for?
This is for pthreads. When a pthread exits, its shadow stack needs to
be freed.
next prev parent reply other threads:[~2018-06-07 17:50 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 [this message]
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
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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