From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ex13-edg-ou-002.vmware.com ([208.91.0.190]:7262 "EHLO EX13-EDG-OU-002.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727204AbeH2MYT (ORCPT ); Wed, 29 Aug 2018 08:24:19 -0400 From: Nadav Amit Subject: [RFC PATCH 2/6] x86/mm: temporary mm struct Date: Wed, 29 Aug 2018 01:11:43 -0700 Message-ID: <20180829081147.184610-3-namit@vmware.com> In-Reply-To: <20180829081147.184610-1-namit@vmware.com> References: <20180829081147.184610-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-arch-owner@vger.kernel.org List-ID: To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Ingo Molnar , x86@kernel.org, Arnd Bergmann , linux-arch@vger.kernel.org, Andy Lutomirski , Masami Hiramatsu , Kees Cook , Peter Zijlstra , Nadav Amit Message-ID: <20180829081143.JgmySGwoB-60bTZR6KmDyRUYSaY3vV0eOtdDvwsk7Nw@z> From: Andy Lutomirski Sometimes we want to set a temporary page-table entries (PTEs) in one of the cores, without allowing other cores to use - even speculatively - these mappings. There are two benefits for doing so: (1) Security: if sensitive PTEs are set, temporary mm prevents their use in other cores. This hardens the security as it prevents exploding a dangling pointer to overwrite sensitive data using the sensitive PTE. (2) Avoiding TLB shootdowns: the PTEs do not need to be flushed in remote page-tables. To do so a temporary mm_struct can be used. Mappings which are private for this mm can be set in the userspace part of the address-space. During the whole time in which the temporary mm is loaded, interrupts must be disabled. The first use-case for temporary PTEs, which will follow, is for poking the kernel text. [ Commit message was written by Nadav ] Cc: Andy Lutomirski Cc: Masami Hiramatsu Cc: Kees Cook Cc: Peter Zijlstra Signed-off-by: Nadav Amit --- arch/x86/include/asm/mmu_context.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index eeeb9289c764..96afc8c0cf15 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -338,4 +338,24 @@ static inline unsigned long __get_current_cr3_fast(void) return cr3; } +typedef struct { + struct mm_struct *prev; +} temporary_mm_state_t; + +static inline temporary_mm_state_t use_temporary_mm(struct mm_struct *mm) +{ + temporary_mm_state_t state; + + lockdep_assert_irqs_disabled(); + state.prev = this_cpu_read(cpu_tlbstate.loaded_mm); + switch_mm_irqs_off(NULL, mm, current); + return state; +} + +static inline void unuse_temporary_mm(temporary_mm_state_t prev) +{ + lockdep_assert_irqs_disabled(); + switch_mm_irqs_off(NULL, prev.prev, current); +} + #endif /* _ASM_X86_MMU_CONTEXT_H */ -- 2.17.1