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 01/10] x86/cet: User-mode shadow stack support
Date: Thu, 7 Jun 2018 09:37:05 -0700 [thread overview]
Message-ID: <CALCETrX4ALKbphJiZs4MXWtRFvQYD905bNAMTogbOeLh0Pp6xw@mail.gmail.com> (raw)
In-Reply-To: <20180607143807.3611-2-yu-cheng.yu@intel.com>
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?
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.)
> +#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.
> +
> +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.
> +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.
> +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.)
> +
> + 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?
> +
> + /*
> + * 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?
next prev parent reply other threads:[~2018-06-07 16:37 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 [this message]
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
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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