From patchwork Thu Sep 29 22:29:22 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Edgecombe, Rick P" X-Patchwork-Id: 12994679 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5BA2C43219 for ; Thu, 29 Sep 2022 22:30:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B75D18D0013; Thu, 29 Sep 2022 18:30:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B274B8D000C; Thu, 29 Sep 2022 18:30:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9A1188D0013; Thu, 29 Sep 2022 18:30:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 856C18D000C for ; Thu, 29 Sep 2022 18:30:42 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 60BE51213F0 for ; Thu, 29 Sep 2022 22:30:42 +0000 (UTC) X-FDA: 79966568724.21.033F3D1 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf02.hostedemail.com (Postfix) with ESMTP id C304280014 for ; Thu, 29 Sep 2022 22:30:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1664490641; x=1696026641; h=from:to:cc:subject:date:message-id:in-reply-to: references; bh=sfY0qfAAMaBKBaoxmspQvWEjmGcNq7mh/op82wqEfzo=; b=MNfFuXwJJZBLf0pX1oF1YTAq60D4LAKeO+KZzASVT2TXcFW1epgG1o+l w/k3IvlTWMIV5wKjcf8dAsOIKkqFACJQFTKlJ7ZjiyccT0d2iBfHjwGeA 4BejpMO1gF+EbQaJZBOds59U+J8IcubfIm7PE03k0EG3ReyCUsC1NgI/n i2cZWIKUr77RWeazIvQIHiWA4IIBrVMfxGoGE7tyPa4a09/lkFsifzTLg DvyIFMcBEVFo1RvrAx/iOdTi2Tca/X6zMtqoFYDGGBCfuxOVKoYsFgVfV q57dfXZ6xjQcMpBh9KSvfl3aUxeaHEOony1rTwlD4FiyEx6V4833Z8UZS w==; X-IronPort-AV: E=McAfee;i="6500,9779,10485"; a="289207517" X-IronPort-AV: E=Sophos;i="5.93,356,1654585200"; d="scan'208";a="289207517" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Sep 2022 15:30:40 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10485"; a="691016319" X-IronPort-AV: E=Sophos;i="5.93,356,1654585200"; d="scan'208";a="691016319" Received: from sergungo-mobl.amr.corp.intel.com (HELO rpedgeco-desk.amr.corp.intel.com) ([10.251.25.88]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Sep 2022 15:30:38 -0700 From: Rick Edgecombe To: x86@kernel.org, "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , 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 , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V . Shankar" , Weijiang Yang , "Kirill A . Shutemov" , joao.moreira@intel.com, John Allen , kcc@google.com, eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com, dethoma@microsoft.com Cc: rick.p.edgecombe@intel.com, Yu-cheng Yu Subject: [PATCH v2 25/39] x86/cet/shstk: Handle thread shadow stack Date: Thu, 29 Sep 2022 15:29:22 -0700 Message-Id: <20220929222936.14584-26-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220929222936.14584-1-rick.p.edgecombe@intel.com> References: <20220929222936.14584-1-rick.p.edgecombe@intel.com> ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=MNfFuXwJ; spf=pass (imf02.hostedemail.com: domain of rick.p.edgecombe@intel.com designates 134.134.136.20 as permitted sender) smtp.mailfrom=rick.p.edgecombe@intel.com; dmarc=pass (policy=none) header.from=intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664490642; a=rsa-sha256; cv=none; b=n4171uN6Mg54F0kE5ZDD5YNMTvi2swaNaS4iT3GEwEm5IBP54dLo8K9U0JWIRXKO+CyPZ3 WlAEb6EAdQhrCxSay8Ffji/pdWBw0yNx+VJg6OFByxieWTnAJtI1XKLiC5zN3C5z6awx1q f7vj0zS7PxVhYIRi9u2KDqP9TZOM8sE= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664490642; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references:dkim-signature; bh=enSeqn6/zMbUDQ8oNusi22DzvIgvNm7w+oXXQu9Ss8w=; b=TiqRmuI32VGHqQFa9WTr5ReG0Mykzkw70oztHFpX1n1ykpoCuUxmpdmawJsL8v5JTKOpjq jouY041UCML5ohuHe63+N1k5cqAGra5lxw30P6pGACHmarEfiIlVur7DFR8jkXeZpoaJMl CqCMBxRKYj9tq2ypAZK/na+F2RUUBp8= Authentication-Results: imf02.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=MNfFuXwJ; spf=pass (imf02.hostedemail.com: domain of rick.p.edgecombe@intel.com designates 134.134.136.20 as permitted sender) smtp.mailfrom=rick.p.edgecombe@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Rspam-User: X-Stat-Signature: zbkcfbpycawj634mcgmxbpt79eisrbyc X-Rspamd-Queue-Id: C304280014 X-Rspamd-Server: rspam05 X-HE-Tag: 1664490641-429646 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Yu-cheng Yu When a process is duplicated, but the child shares the address space with the parent, there is potential for the threads sharing a single stack to cause conflicts for each other. In the normal non-cet case this is handled in two ways. With regular CLONE_VM a new stack is provided by userspace such that the parent and child have different stacks. For vfork, the parent is suspended until the child exits. So as long as the child doesn't return from the vfork()/CLONE_VFORK calling function and sticks to a limited set of operations, the parent and child can share the same stack. For shadow stack, these scenarios present similar sharing problems. For the CLONE_VM case, the child and the parent must have separate shadow stacks. Instead of changing clone to take a shadow stack, have the kernel just allocate one and switch to it. Use stack_size passed from clone3() syscall for thread shadow stack size. A compat-mode thread shadow stack size is further reduced to 1/4. This allows more threads to run in a 32-bit address space. The clone() does not pass stack_size, which was added to clone3(). In that case, use RLIMIT_STACK size and cap to 4 GB. For shadow stack enabled vfork(), the parent and child can share the same shadow stack, like they can share a normal stack. Since the parent is suspended until the child terminates, the child will not interfere with the parent while executing as long as it doesn't return from the vfork() and overwrite up the shadow stack. The child can safely overwrite down the shadow stack, as the parent can just overwrite this later. So CET does not add any additional limitations for vfork(). Userspace implementing posix vfork() can actually prevent the child from returning from the vfork() calling function, using CET. Glibc does this by adjusting the shadow stack pointer in the child, so that the child receives a #CP if it tries to return from vfork() calling function. Free the shadow stack on thread exit by doing it in mm_release(). Skip this when exiting a vfork() child since the stack is shared in the parent. During this operation, the shadow stack pointer of the new thread needs to be updated to point to the newly allocated shadow stack. Since the ability to do this is confined to the FPU subsystem, change fpu_clone() to take the new shadow stack pointer, and update it internally inside the FPU subsystem. This part was suggested by Thomas Gleixner. Suggested-by: Thomas Gleixner Signed-off-by: Yu-cheng Yu Co-developed-by: Rick Edgecombe Signed-off-by: Rick Edgecombe --- v2: - Have fpu_clone() take new shadow stack pointer and update SSP in xsave buffer for new task. (tglx) v1: - Expand commit log. - Add more comments. - Switch to xsave helpers. Yu-cheng v30: - Update comments about clone()/clone3(). (Borislav Petkov) Yu-cheng v29: - WARN_ON_ONCE() when get_xsave_addr() returns NULL, and update comments. (Dave Hansen) arch/x86/include/asm/cet.h | 7 +++++ arch/x86/include/asm/fpu/sched.h | 3 +- arch/x86/include/asm/mmu_context.h | 2 ++ arch/x86/kernel/fpu/core.c | 40 ++++++++++++++++++++++++- arch/x86/kernel/process.c | 17 ++++++++++- arch/x86/kernel/shstk.c | 48 +++++++++++++++++++++++++++++- 6 files changed, 113 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h index a4a1f4c0089b..924de99e0c61 100644 --- a/arch/x86/include/asm/cet.h +++ b/arch/x86/include/asm/cet.h @@ -16,6 +16,9 @@ struct thread_shstk { long cet_prctl(struct task_struct *task, int option, unsigned long features); int shstk_setup(void); +int shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags, + unsigned long stack_size, + unsigned long *shstk_addr); void shstk_free(struct task_struct *p); int shstk_disable(void); void reset_thread_shstk(void); @@ -23,6 +26,10 @@ void reset_thread_shstk(void); static inline long cet_prctl(struct task_struct *task, int option, unsigned long features) { return -EINVAL; } static inline int shstk_setup(void) { return -EOPNOTSUPP; } +static inline int shstk_alloc_thread_stack(struct task_struct *p, + unsigned long clone_flags, + unsigned long stack_size, + unsigned long *shstk_addr) { return 0; } static inline void shstk_free(struct task_struct *p) {} static inline int shstk_disable(void) { return -EOPNOTSUPP; } static inline void reset_thread_shstk(void) {} diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h index b2486b2cbc6e..54c9c2fd1907 100644 --- a/arch/x86/include/asm/fpu/sched.h +++ b/arch/x86/include/asm/fpu/sched.h @@ -11,7 +11,8 @@ extern void save_fpregs_to_fpstate(struct fpu *fpu); extern void fpu__drop(struct fpu *fpu); -extern int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal); +extern int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal, + unsigned long shstk_addr); extern void fpu_flush_thread(void); /* diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index b8d40ddeab00..d29988cbdf20 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -146,6 +146,8 @@ do { \ #else #define deactivate_mm(tsk, mm) \ do { \ + if (!tsk->vfork_done) \ + shstk_free(tsk); \ load_gs_index(0); \ loadsegment(fs, 0); \ } while (0) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 778d3054ccc7..f332e9b42b6d 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -555,8 +555,40 @@ static inline void fpu_inherit_perms(struct fpu *dst_fpu) } } +#ifdef CONFIG_X86_SHADOW_STACK +static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp) +{ + struct cet_user_state *xstate; + + /* If ssp update is not needed. */ + if (!ssp) + return 0; + + xstate = get_xsave_addr(&dst->thread.fpu.fpstate->regs.xsave, + XFEATURE_CET_USER); + + /* + * If there is a non-zero ssp, then 'dst' must be configured with a shadow + * stack and the fpu state should be up to date since it was just copied + * from the parent in fpu_clone(). So there must be a valid non-init CET + * state location in the buffer. + */ + if (WARN_ON_ONCE(!xstate)) + return 1; + + xstate->user_ssp = (u64)ssp; + + return 0; +} +#else +static int update_fpu_shstk(struct task_struct *dst, unsigned long shstk_addr) +{ +} +#endif + /* Clone current's FPU state on fork */ -int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal) +int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal, + unsigned long ssp) { struct fpu *src_fpu = ¤t->thread.fpu; struct fpu *dst_fpu = &dst->thread.fpu; @@ -616,6 +648,12 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal) if (use_xsave()) dst_fpu->fpstate->regs.xsave.header.xfeatures &= ~XFEATURE_MASK_PASID; + /* + * Update shadow stack pointer, in case it changed during clone. + */ + if (update_fpu_shstk(dst, ssp)) + return 1; + trace_x86_fpu_copy_src(src_fpu); trace_x86_fpu_copy_dst(dst_fpu); diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 034880311e6b..5e63d190becd 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -47,6 +47,7 @@ #include #include #include +#include #include "process.h" @@ -118,6 +119,7 @@ void exit_thread(struct task_struct *tsk) free_vm86(t); + shstk_free(tsk); fpu__drop(fpu); } @@ -139,6 +141,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) struct inactive_task_frame *frame; struct fork_frame *fork_frame; struct pt_regs *childregs; + unsigned long shstk_addr = 0; int ret = 0; childregs = task_pt_regs(p); @@ -173,7 +176,12 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) frame->flags = X86_EFLAGS_FIXED; #endif - fpu_clone(p, clone_flags, args->fn); + /* Allocate a new shadow stack for pthread if needed */ + ret = shstk_alloc_thread_stack(p, clone_flags, args->flags, &shstk_addr); + if (ret) + return ret; + + fpu_clone(p, clone_flags, args->fn, shstk_addr); /* Kernel thread ? */ if (unlikely(p->flags & PF_KTHREAD)) { @@ -219,6 +227,13 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP))) io_bitmap_share(p); + /* + * If copy_thread() if failing, don't leak the shadow stack possibly + * allocated in shstk_alloc_thread_stack() above. + */ + if (ret) + shstk_free(p); + return ret; } diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c index a0b8d4adb2bf..db4e53f9fdaf 100644 --- a/arch/x86/kernel/shstk.c +++ b/arch/x86/kernel/shstk.c @@ -118,6 +118,46 @@ void reset_thread_shstk(void) current->thread.features_locked = 0; } +int shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long clone_flags, + unsigned long stack_size, unsigned long *shstk_addr) +{ + struct thread_shstk *shstk = &tsk->thread.shstk; + unsigned long addr; + + /* + * If shadow stack is not enabled on the new thread, skip any + * switch to a new shadow stack. + */ + if (!feature_enabled(CET_SHSTK)) + return 0; + + /* + * clone() does not pass stack_size, which was added to clone3(). + * Use RLIMIT_STACK and cap to 4 GB. + */ + if (!stack_size) + stack_size = min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G); + + /* + * For CLONE_VM, except vfork, the child needs a separate shadow + * stack. + */ + if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM) + return 0; + + + stack_size = PAGE_ALIGN(stack_size); + if (IS_ERR_VALUE(addr)) + return PTR_ERR((void *)addr); + + shstk->base = addr; + shstk->size = stack_size; + + *shstk_addr = addr + stack_size; + + return 0; +} + void shstk_free(struct task_struct *tsk) { struct thread_shstk *shstk = &tsk->thread.shstk; @@ -126,7 +166,13 @@ void shstk_free(struct task_struct *tsk) !feature_enabled(CET_SHSTK)) return; - if (!tsk->mm) + /* + * When fork() with CLONE_VM fails, the child (tsk) already has a + * shadow stack allocated, and exit_thread() calls this function to + * free it. In this case the parent (current) and the child share + * the same mm struct. + */ + if (!tsk->mm || tsk->mm != current->mm) return; unmap_shadow_stack(shstk->base, shstk->size);