From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47E37C83001 for ; Wed, 29 Apr 2020 02:15:28 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F252320730 for ; Wed, 29 Apr 2020 02:15:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F252320730 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49Bhtj3PMWzDqyh for ; Wed, 29 Apr 2020 12:15:25 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=informatik.wtf (client-ip=131.153.2.45; helo=h4.fbrelay.privateemail.com; envelope-from=cmr@informatik.wtf; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Received: from h4.fbrelay.privateemail.com (h4.fbrelay.privateemail.com [131.153.2.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 49Bhdy0ZtmzDqyG for ; Wed, 29 Apr 2020 12:04:22 +1000 (AEST) Received: from MTA-14-4.privateemail.com (mta-14.privateemail.com [198.54.118.205]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by h3.fbrelay.privateemail.com (Postfix) with ESMTPS id 8080A8084E for ; Tue, 28 Apr 2020 22:04:17 -0400 (EDT) Received: from mta-14.privateemail.com (localhost [127.0.0.1]) by mta-14.privateemail.com (Postfix) with ESMTP id 3DFE780053; Tue, 28 Apr 2020 22:04:13 -0400 (EDT) Received: from geist.attlocal.net (unknown [10.20.151.249]) by mta-14.privateemail.com (Postfix) with ESMTPA id BA9B680059; Wed, 29 Apr 2020 02:04:12 +0000 (UTC) From: "Christopher M. Riedl" To: linuxppc-dev@lists.ozlabs.org, kernel-hardening@lists.openwall.com Subject: [RFC PATCH v2 1/5] powerpc/mm: Introduce temporary mm Date: Tue, 28 Apr 2020 21:05:27 -0500 Message-Id: <20200429020531.20684-2-cmr@informatik.wtf> X-Mailer: git-send-email 2.26.1 In-Reply-To: <20200429020531.20684-1-cmr@informatik.wtf> References: <20200429020531.20684-1-cmr@informatik.wtf> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Virus-Scanned: ClamAV using ClamSMTP X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" x86 supports the notion of a temporary mm which restricts access to temporary PTEs to a single CPU. A temporary mm is useful for situations where a CPU needs to perform sensitive operations (such as patching a STRICT_KERNEL_RWX kernel) requiring temporary mappings without exposing said mappings to other CPUs. A side benefit is that other CPU TLBs do not need to be flushed when the temporary mm is torn down. Mappings in the temporary mm can be set in the userspace portion of the address-space. Interrupts must be disabled while the temporary mm is in use. HW breakpoints, which may have been set by userspace as watchpoints on addresses now within the temporary mm, are saved and disabled when loading the temporary mm. The HW breakpoints are restored when unloading the temporary mm. All HW breakpoints are indiscriminately disabled while the temporary mm is in use. Based on x86 implementation: commit cefa929c034e ("x86/mm: Introduce temporary mm structs") Signed-off-by: Christopher M. Riedl --- arch/powerpc/include/asm/debug.h | 1 + arch/powerpc/include/asm/mmu_context.h | 54 ++++++++++++++++++++++++++ arch/powerpc/kernel/process.c | 5 +++ 3 files changed, 60 insertions(+) diff --git a/arch/powerpc/include/asm/debug.h b/arch/powerpc/include/asm/debug.h index 7756026b95ca..b945bc16c932 100644 --- a/arch/powerpc/include/asm/debug.h +++ b/arch/powerpc/include/asm/debug.h @@ -45,6 +45,7 @@ static inline int debugger_break_match(struct pt_regs *regs) { return 0; } static inline int debugger_fault_handler(struct pt_regs *regs) { return 0; } #endif +void __get_breakpoint(struct arch_hw_breakpoint *brk); void __set_breakpoint(struct arch_hw_breakpoint *brk); bool ppc_breakpoint_available(void); #ifdef CONFIG_PPC_ADV_DEBUG_REGS diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h index 360367c579de..57a8695fe63f 100644 --- a/arch/powerpc/include/asm/mmu_context.h +++ b/arch/powerpc/include/asm/mmu_context.h @@ -10,6 +10,7 @@ #include #include #include +#include /* * Most if the context management is out of line @@ -270,5 +271,58 @@ static inline int arch_dup_mmap(struct mm_struct *oldmm, return 0; } +struct temp_mm { + struct mm_struct *temp; + struct mm_struct *prev; + bool is_kernel_thread; + struct arch_hw_breakpoint brk; +}; + +static inline void init_temp_mm(struct temp_mm *temp_mm, struct mm_struct *mm) +{ + temp_mm->temp = mm; + temp_mm->prev = NULL; + temp_mm->is_kernel_thread = false; + memset(&temp_mm->brk, 0, sizeof(temp_mm->brk)); +} + +static inline void use_temporary_mm(struct temp_mm *temp_mm) +{ + lockdep_assert_irqs_disabled(); + + temp_mm->is_kernel_thread = current->mm == NULL; + if (temp_mm->is_kernel_thread) + temp_mm->prev = current->active_mm; + else + temp_mm->prev = current->mm; + + /* + * Hash requires a non-NULL current->mm to allocate a userspace address + * when handling a page fault. Does not appear to hurt in Radix either. + */ + current->mm = temp_mm->temp; + switch_mm_irqs_off(NULL, temp_mm->temp, current); + + if (ppc_breakpoint_available()) { + __get_breakpoint(&temp_mm->brk); + if (temp_mm->brk.type != 0) + hw_breakpoint_disable(); + } +} + +static inline void unuse_temporary_mm(struct temp_mm *temp_mm) +{ + lockdep_assert_irqs_disabled(); + + if (temp_mm->is_kernel_thread) + current->mm = NULL; + else + current->mm = temp_mm->prev; + switch_mm_irqs_off(NULL, temp_mm->prev, current); + + if (ppc_breakpoint_available() && temp_mm->brk.type != 0) + __set_breakpoint(&temp_mm->brk); +} + #endif /* __KERNEL__ */ #endif /* __ASM_POWERPC_MMU_CONTEXT_H */ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 9c21288f8645..ec4cf890d92c 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -800,6 +800,11 @@ static inline int set_breakpoint_8xx(struct arch_hw_breakpoint *brk) return 0; } +void __get_breakpoint(struct arch_hw_breakpoint *brk) +{ + memcpy(brk, this_cpu_ptr(¤t_brk), sizeof(*brk)); +} + void __set_breakpoint(struct arch_hw_breakpoint *brk) { memcpy(this_cpu_ptr(¤t_brk), brk, sizeof(*brk)); -- 2.26.1