From patchwork Thu Sep 29 22:29:15 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: 12994672 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 D5001C43219 for ; Thu, 29 Sep 2022 22:30:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3D56D8D0001; Thu, 29 Sep 2022 18:30:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 35D5D8D000D; Thu, 29 Sep 2022 18:30:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 13BE58D0001; Thu, 29 Sep 2022 18:30:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id E20398D000C for ; Thu, 29 Sep 2022 18:30:26 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id B9E1A1C6E4A for ; Thu, 29 Sep 2022 22:30:26 +0000 (UTC) X-FDA: 79966568052.10.D99392B Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by imf26.hostedemail.com (Postfix) with ESMTP id 3BADB14000B for ; Thu, 29 Sep 2022 22:30:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1664490626; x=1696026626; h=from:to:cc:subject:date:message-id:in-reply-to: references; bh=a9AIyyilAohGDoPHrssf1eNaoetpft93CZ4gQ0mvYLg=; b=bzzlnu1MAkqlHia0g9m+JOg5ND1GSgo1IHX8bjySy/ADH5vUdMfSzJsv 8TeUaEdyJUP+DoLxcEQJCJbT+HmsJIJMOct3pWzYbnQhALtKTunXrC+d+ 95amfp4KVtwzTmmH+qEz8c8mviIhteh9Wz6iZSv5YwhsR7chv6LZvJTgI M+zYWdEtjCbi2ZabbyVBw4JQaJNMf8xU9V2NRJ6iHFpKHktnv1+kxuYUt riNsr4+homX2tLnOhPX9Qh1Sh4clp0i5TYo82Qnkk/feBNME3+yuSzh7p KY29r1R2jJHdakqNuP1oN4X6X0kP4/4i2NtoC4v7tE3NSZGcurESGLfr1 g==; X-IronPort-AV: E=McAfee;i="6500,9779,10485"; a="328420483" X-IronPort-AV: E=Sophos;i="5.93,356,1654585200"; d="scan'208";a="328420483" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Sep 2022 15:30:24 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10485"; a="691016239" X-IronPort-AV: E=Sophos;i="5.93,356,1654585200"; d="scan'208";a="691016239" 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 15:30:20 -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 18/39] mm: Add guard pages around a shadow stack. Date: Thu, 29 Sep 2022 15:29:15 -0700 Message-Id: <20220929222936.14584-19-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-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664490626; 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=mFZ/2ILHxyUz8oUv7NSDjOnndkwzMgPd0BSIOD2PQY8=; b=HpWkGJSLis9AVWgqJOVygq0XW0gfKG2XWvkkXnlLHtDIhsxqpOpmUtqnYUtJWkeJwNGK8E RFTi4BMxqRUnI827ps/y0EVN5sNisSoY9d99p8P4Pti5TT7Tl2TFhUTpBaNPK152MB5mhk gW1xCRoPbd/QPv+/e81sClXjnSEk3Vg= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=bzzlnu1M; spf=pass (imf26.hostedemail.com: domain of rick.p.edgecombe@intel.com designates 192.55.52.88 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=1664490626; a=rsa-sha256; cv=none; b=jD/FNKHO8d9pcfFtDE4D1jpz3xX5TV9r8gHFtgYBMFnEfKMjiA0e/XH0j9AIzrFDrKkmFU D4Uf8ZnbdVNgdI8bWWXppScGUlbYy5wj5ChSSVKgdBzXSy8AqRDafIrOzOJHTQo/CxPKQj /n/Qg0kLh+y7UuT3ZSVUndDdysPPM38= Authentication-Results: imf26.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=bzzlnu1M; spf=pass (imf26.hostedemail.com: domain of rick.p.edgecombe@intel.com designates 192.55.52.88 as permitted sender) smtp.mailfrom=rick.p.edgecombe@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Rspam-User: X-Stat-Signature: t4xw5io8gsdgm7f6xdydwniz9dee7rec X-Rspamd-Queue-Id: 3BADB14000B X-Rspamd-Server: rspam08 X-HE-Tag: 1664490626-630417 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 The architecture of shadow stack constrains the ability of userspace to move the shadow stack pointer (SSP) in order to prevent corrupting or switching to other shadow stacks. The RSTORSSP can move the spp to different shadow stacks, but it requires a specially placed token in order to do this. However, the architecture does not prevent incrementing the stack pointer to wander onto an adjacent shadow stack. To prevent this in software, enforce guard pages at the beginning of shadow stack vmas, such that there will always be a gap between adjacent shadow stacks. Make the gap big enough so that no userspace SSP changing operations (besides RSTORSSP), can move the SSP from one stack to the next. The SSP can increment or decrement by CALL, RET and INCSSP. CALL and RET can move the SSP by a maximum of 8 bytes, at which point the shadow stack would be accessed. The INCSSP instruction can also increment the shadow stack pointer. It is the shadow stack analog of an instruction like: addq $0x80, %rsp However, there is one important difference between an ADD on %rsp and INCSSP. In addition to modifying SSP, INCSSP also reads from the memory of the first and last elements that were "popped". It can be thought of as acting like this: READ_ONCE(ssp); // read+discard top element on stack ssp += nr_to_pop * 8; // move the shadow stack READ_ONCE(ssp-8); // read+discard last popped stack element The maximum distance INCSSP can move the SSP is 2040 bytes, before it would read the memory. Therefore a single page gap will be enough to prevent any operation from shifting the SSP to an adjacent stack, since it would have to land in the gap at least once, causing a fault. This could be accomplished by using VM_GROWSDOWN, but this has a downside. The behavior would allow shadow stack's to grow, which is unneeded and adds a strange difference to how most regular stacks work. Signed-off-by: Yu-cheng Yu Co-developed-by: Rick Edgecombe Signed-off-by: Rick Edgecombe Cc: Kees Cook Reviewed-by: Kees Cook --- v2: - Use __weak instead of #ifdef (Dave Hansen) - Only have start gap on shadow stack (Andy Luto) - Create stack_guard_start_gap() to not duplicate code in an arch version of vm_start_gap() (Dave Hansen) - Improve commit log partly with verbiage from (Dave Hansen) Yu-cheng v25: - Move SHADOW_STACK_GUARD_GAP to arch/x86/mm/mmap.c. Yu-cheng v24: - Instead changing vm_*_gap(), create x86-specific versions. arch/x86/mm/mmap.c | 23 +++++++++++++++++++++++ include/linux/mm.h | 11 ++++++----- mm/mmap.c | 7 +++++++ 3 files changed, 36 insertions(+), 5 deletions(-) diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index f3f52c5e2fd6..b0427bd2da30 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -250,3 +250,26 @@ bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot) return false; return true; } + +unsigned long stack_guard_start_gap(struct vm_area_struct *vma) +{ + if (vma->vm_flags & VM_GROWSDOWN) + return stack_guard_gap; + + /* + * Shadow stack pointer is moved by CALL, RET, and INCSSP(Q/D). + * INCSSPQ moves shadow stack pointer up to 255 * 8 = ~2 KB + * (~1KB for INCSSPD) and touches the first and the last element + * in the range, which triggers a page fault if the range is not + * in a shadow stack. Because of this, creating 4-KB guard pages + * around a shadow stack prevents these instructions from going + * beyond. + * + * Creation of VM_SHADOW_STACK is tightly controlled, so a vma + * can't be both VM_GROWSDOWN and VM_SHADOW_STACK + */ + if (vma->vm_flags & VM_SHADOW_STACK) + return PAGE_SIZE; + + return 0; +} diff --git a/include/linux/mm.h b/include/linux/mm.h index fef14ab3abcb..09458e77bf52 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2775,15 +2775,16 @@ struct vm_area_struct *vma_lookup(struct mm_struct *mm, unsigned long addr) return vma; } +unsigned long stack_guard_start_gap(struct vm_area_struct *vma); + static inline unsigned long vm_start_gap(struct vm_area_struct *vma) { + unsigned long gap = stack_guard_start_gap(vma); unsigned long vm_start = vma->vm_start; - if (vma->vm_flags & VM_GROWSDOWN) { - vm_start -= stack_guard_gap; - if (vm_start > vma->vm_start) - vm_start = 0; - } + vm_start -= gap; + if (vm_start > vma->vm_start) + vm_start = 0; return vm_start; } diff --git a/mm/mmap.c b/mm/mmap.c index 9d780f415be3..f0d2e9143bd0 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -247,6 +247,13 @@ SYSCALL_DEFINE1(brk, unsigned long, brk) return origbrk; } +unsigned long __weak stack_guard_start_gap(struct vm_area_struct *vma) +{ + if (vma->vm_flags & VM_GROWSDOWN) + return stack_guard_gap; + return 0; +} + static inline unsigned long vma_compute_gap(struct vm_area_struct *vma) { unsigned long gap, prev_end;