From: Kees Cook <keescook@chromium.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: 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>,
Andy Lutomirski <luto@kernel.org>,
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>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
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>,
x86-patch-review@intel.com
Subject: Re: [RFC PATCH v9 25/27] x86/cet/shstk: Handle thread Shadow Stack
Date: Tue, 25 Feb 2020 13:29:12 -0800 [thread overview]
Message-ID: <202002251324.5D515260@keescook> (raw)
In-Reply-To: <20200205181935.3712-26-yu-cheng.yu@intel.com>
On Wed, Feb 05, 2020 at 10:19:33AM -0800, Yu-cheng Yu wrote:
> The Shadow Stack (SHSTK) for clone/fork is handled as the following:
>
> (1) If ((clone_flags & (CLONE_VFORK | CLONE_VM)) == CLONE_VM),
> the kernel allocates (and frees on thread exit) a new SHSTK for the
> child.
>
> It is possible for the kernel to complete the clone syscall and set the
> child's SHSTK pointer to NULL and let the child thread allocate a SHSTK
> for itself. There are two issues in this approach: It is not
> compatible with existing code that does inline syscall and it cannot
> handle signals before the child can successfully allocate a SHSTK.
>
> (2) For (clone_flags & CLONE_VFORK), the child uses the existing SHSTK.
>
> (3) For all other cases, the SHSTK is copied/reused whenever the parent or
> the child does a call/ret.
>
> This patch handles cases (1) & (2). Case (3) is handled in the SHSTK page
> fault patches.
>
> A 64-bit SHSTK has a fixed size of RLIMIT_STACK. A compat-mode thread SHSTK
> has a fixed size of 1/4 RLIMIT_STACK. This allows more threads to share a
> 32-bit address space.
I am not understanding this part. :) Entries are sizeof(unsigned long),
yes? A 1/2 RLIMIT_STACK would cover 32-bit, but 1/4 is less, so why does
that provide for more threads?
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> arch/x86/include/asm/cet.h | 2 ++
> arch/x86/include/asm/mmu_context.h | 3 +++
> arch/x86/kernel/cet.c | 41 ++++++++++++++++++++++++++++++
> arch/x86/kernel/process.c | 7 +++++
> 4 files changed, 53 insertions(+)
>
> diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h
> index 409d4f91a0dc..9a3e2da9c1c4 100644
> --- a/arch/x86/include/asm/cet.h
> +++ b/arch/x86/include/asm/cet.h
> @@ -19,10 +19,12 @@ struct cet_status {
>
> #ifdef CONFIG_X86_INTEL_CET
> int cet_setup_shstk(void);
> +int cet_setup_thread_shstk(struct task_struct *p);
> void cet_disable_free_shstk(struct task_struct *p);
> int cet_restore_signal(bool ia32, struct sc_ext *sc);
> int cet_setup_signal(bool ia32, unsigned long rstor, struct sc_ext *sc);
> #else
> +static inline int cet_setup_thread_shstk(struct task_struct *p) { return 0; }
> static inline void cet_disable_free_shstk(struct task_struct *p) {}
> static inline int cet_restore_signal(bool ia32, struct sc_ext *sc) { return -EINVAL; }
> static inline int cet_setup_signal(bool ia32, unsigned long rstor,
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 5f33924e200f..6a8189308823 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -13,6 +13,7 @@
> #include <asm/tlbflush.h>
> #include <asm/paravirt.h>
> #include <asm/mpx.h>
> +#include <asm/cet.h>
> #include <asm/debugreg.h>
>
> extern atomic64_t last_mm_ctx_id;
> @@ -230,6 +231,8 @@ do { \
> #else
> #define deactivate_mm(tsk, mm) \
> do { \
> + if (!tsk->vfork_done) \
> + cet_disable_free_shstk(tsk); \
> load_gs_index(0); \
> loadsegment(fs, 0); \
> } while (0)
> diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
> index cba5c7656aab..5b45abda80a1 100644
> --- a/arch/x86/kernel/cet.c
> +++ b/arch/x86/kernel/cet.c
> @@ -170,6 +170,47 @@ int cet_setup_shstk(void)
> return 0;
> }
>
> +int cet_setup_thread_shstk(struct task_struct *tsk)
> +{
> + unsigned long addr, size;
> + struct cet_user_state *state;
> + struct cet_status *cet = &tsk->thread.cet;
> +
> + if (!cet->shstk_enabled)
> + return 0;
> +
> + state = get_xsave_addr(&tsk->thread.fpu.state.xsave,
> + XFEATURE_CET_USER);
> +
> + if (!state)
> + return -EINVAL;
> +
> + size = rlimit(RLIMIT_STACK);
Is SHSTK incompatible with RLIM_INFINITY stack rlimits?
> +
> + /*
> + * Compat-mode pthreads share a limited address space.
> + * If each function call takes an average of four slots
> + * stack space, we need 1/4 of stack size for shadow stack.
> + */
> + if (in_compat_syscall())
> + size /= 4;
> +
> + addr = alloc_shstk(size);
I assume it'd fail here, but I worry about Stack Clash style attacks.
I'd like to see test cases that make sure the SHSTK gap is working
correctly.
-Kees
> +
> + if (IS_ERR((void *)addr)) {
> + cet->shstk_base = 0;
> + cet->shstk_size = 0;
> + cet->shstk_enabled = 0;
> + return PTR_ERR((void *)addr);
> + }
> +
> + fpu__prepare_write(&tsk->thread.fpu);
> + state->user_ssp = (u64)(addr + size);
> + cet->shstk_base = addr;
> + cet->shstk_size = size;
> + return 0;
> +}
> +
> void cet_disable_free_shstk(struct task_struct *tsk)
> {
> struct cet_status *cet = &tsk->thread.cet;
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index e102e63de641..7098618142f2 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -110,6 +110,7 @@ void exit_thread(struct task_struct *tsk)
>
> free_vm86(t);
>
> + cet_disable_free_shstk(tsk);
> fpu__drop(fpu);
> }
>
> @@ -180,6 +181,12 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
> if (clone_flags & CLONE_SETTLS)
> ret = set_new_tls(p, tls);
>
> +#ifdef CONFIG_X86_64
> + /* Allocate a new shadow stack for pthread */
> + if (!ret && (clone_flags & (CLONE_VFORK | CLONE_VM)) == CLONE_VM)
> + ret = cet_setup_thread_shstk(p);
> +#endif
> +
> if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
> io_bitmap_share(p);
>
> --
> 2.21.0
>
--
Kees Cook
next prev parent reply other threads:[~2020-02-25 21:29 UTC|newest]
Thread overview: 107+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 18:19 [RFC PATCH v9 00/27] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 01/27] Documentation/x86: Add CET description Yu-cheng Yu
2020-02-06 0:16 ` Randy Dunlap
[not found] ` <af5ee976-3b57-4afe-6304-fcab8de45c77-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2020-02-06 20:17 ` Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-28 15:55 ` Yu-cheng Yu
2020-02-26 17:57 ` Dave Hansen
2020-03-09 17:00 ` Yu-cheng Yu
2020-03-09 17:21 ` Dave Hansen
2020-03-09 19:27 ` Yu-cheng Yu
2020-03-09 19:35 ` Dave Hansen
2020-03-09 19:50 ` H.J. Lu
2020-03-09 20:16 ` Andy Lutomirski
2020-03-09 20:54 ` H.J. Lu
2020-03-09 20:59 ` Dave Hansen
2020-03-09 21:12 ` H.J. Lu
2020-03-09 22:02 ` Andy Lutomirski
2020-03-09 22:19 ` Dave Hansen
2020-03-09 23:11 ` H.J. Lu
2020-03-09 23:20 ` Dave Hansen
2020-03-09 23:51 ` H.J. Lu
2020-03-09 23:59 ` Andy Lutomirski
2020-03-10 0:08 ` H.J. Lu
2020-03-10 1:21 ` Andy Lutomirski
2020-03-10 2:13 ` H.J. Lu
2020-02-05 18:19 ` [RFC PATCH v9 03/27] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-02-25 20:04 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 04/27] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-02-25 20:06 ` Kees Cook
2020-02-26 17:10 ` Dave Hansen
2020-03-05 20:44 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack memory Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 18:07 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 07/27] Add guard pages around a Shadow Stack Yu-cheng Yu
2020-02-25 20:11 ` Kees Cook
2020-02-26 18:17 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 08/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 18:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 10/27] x86/mm: Update pte_modify, pmd_modify, and _PAGE_CHG_MASK for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-26 22:02 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 11/27] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-02-25 20:13 ` Kees Cook
2020-02-26 22:04 ` Dave Hansen
2020-04-03 15:42 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 13/27] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-02-25 20:16 ` Kees Cook
2020-02-26 22:47 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 14/27] mm: Handle Shadow Stack page fault Yu-cheng Yu
2020-02-25 20:20 ` Kees Cook
2020-03-05 18:30 ` Yu-cheng Yu
2020-02-27 0:08 ` Dave Hansen
2020-04-07 18:14 ` Yu-cheng Yu
2020-04-07 22:21 ` Dave Hansen
2020-04-08 18:18 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB " Yu-cheng Yu
2020-02-25 20:59 ` Kees Cook
2020-03-13 22:00 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow Stack Yu-cheng Yu
2020-02-27 0:34 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 17/27] x86/cet/shstk: User-mode Shadow Stack support Yu-cheng Yu
2020-02-25 21:07 ` Kees Cook
2020-02-27 0:55 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 18/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu
2020-02-25 21:10 ` Kees Cook
2020-03-05 18:39 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 19/27] x86/cet/shstk: Handle signals for Shadow Stack Yu-cheng Yu
2020-02-25 21:17 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 20/27] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 22/27] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-02-25 21:20 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 23/27] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 24/27] x86/cet/shstk: ELF header parsing for Shadow Stack Yu-cheng Yu
2020-02-25 21:22 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 25/27] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-02-25 21:29 ` Kees Cook [this message]
2020-03-25 21:51 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 26/27] mm/mmap: Add Shadow Stack pages to memory accounting Yu-cheng Yu
[not found] ` <20200205181935.3712-1-yu-cheng.yu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2020-02-05 18:19 ` [RFC PATCH v9 02/27] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-02-25 20:02 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection Yu-cheng Yu
2020-02-25 20:07 ` Kees Cook
2020-02-26 17:03 ` Dave Hansen
2020-02-26 19:57 ` Pavel Machek
2020-03-05 20:38 ` Yu-cheng Yu
2020-02-26 18:05 ` Dave Hansen
2020-02-27 1:02 ` H.J. Lu
2020-02-27 1:16 ` Dave Hansen
2020-02-27 2:11 ` H.J. Lu
2020-02-27 3:57 ` Andy Lutomirski
2020-02-27 18:03 ` Dave Hansen
2020-03-06 18:37 ` Yu-cheng Yu
2020-03-06 19:02 ` Dave Hansen
2020-03-06 21:16 ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 09/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:12 ` Kees Cook
2020-02-26 21:35 ` Dave Hansen
2020-04-01 19:08 ` Yu-cheng Yu
2020-04-01 19:22 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 12/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:14 ` Kees Cook
2020-02-26 22:20 ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 21/27] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND Yu-cheng Yu
2020-02-25 21:18 ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 27/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu
2020-02-25 21:31 ` [RFC PATCH v9 00/27] Control-flow Enforcement: " Kees Cook
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