From patchwork Thu Jul 9 04:03:12 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Christopher M. Riedl" X-Patchwork-Id: 11653299 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 58E1460D for ; Thu, 9 Jul 2020 04:01:36 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id BF0E2206E2 for ; Thu, 9 Jul 2020 04:01:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BF0E2206E2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=informatik.wtf Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19262-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 25774 invoked by uid 550); 9 Jul 2020 04:01:22 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 25707 invoked from network); 9 Jul 2020 04:01:21 -0000 From: "Christopher M. Riedl" To: linuxppc-dev@lists.ozlabs.org Cc: kernel-hardening@lists.openwall.com Subject: [PATCH v2 1/5] powerpc/mm: Introduce temporary mm Date: Wed, 8 Jul 2020 23:03:12 -0500 Message-Id: <20200709040316.12789-2-cmr@informatik.wtf> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200709040316.12789-1-cmr@informatik.wtf> References: <20200709040316.12789-1-cmr@informatik.wtf> MIME-Version: 1.0 X-Virus-Scanned: ClamAV using ClamSMTP 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 | 64 ++++++++++++++++++++++++++ arch/powerpc/kernel/process.c | 5 ++ 3 files changed, 70 insertions(+) diff --git a/arch/powerpc/include/asm/debug.h b/arch/powerpc/include/asm/debug.h index ec57daf87f40..827350c9bcf3 100644 --- a/arch/powerpc/include/asm/debug.h +++ b/arch/powerpc/include/asm/debug.h @@ -46,6 +46,7 @@ static inline int debugger_fault_handler(struct pt_regs *regs) { return 0; } #endif void __set_breakpoint(int nr, struct arch_hw_breakpoint *brk); +void __get_breakpoint(int nr, struct arch_hw_breakpoint *brk); bool ppc_breakpoint_available(void); #ifdef CONFIG_PPC_ADV_DEBUG_REGS extern void do_send_trap(struct pt_regs *regs, unsigned long address, diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h index 1a474f6b1992..9269c7c7b04e 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 @@ -300,5 +301,68 @@ 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[HBP_NUM_MAX]; +}; + +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()) { + struct arch_hw_breakpoint null_brk = {0}; + int i = 0; + + for (; i < nr_wp_slots(); ++i) { + __get_breakpoint(i, &temp_mm->brk[i]); + if (temp_mm->brk[i].type != 0) + __set_breakpoint(i, &null_brk); + } + } +} + +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()) { + int i = 0; + + for (; i < nr_wp_slots(); ++i) + if (temp_mm->brk[i].type != 0) + __set_breakpoint(i, &temp_mm->brk[i]); + } +} + #endif /* __KERNEL__ */ #endif /* __ASM_POWERPC_MMU_CONTEXT_H */ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 4650b9bb217f..b6c123bf5edd 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -824,6 +824,11 @@ static inline int set_breakpoint_8xx(struct arch_hw_breakpoint *brk) return 0; } +void __get_breakpoint(int nr, struct arch_hw_breakpoint *brk) +{ + memcpy(brk, this_cpu_ptr(¤t_brk[nr]), sizeof(*brk)); +} + void __set_breakpoint(int nr, struct arch_hw_breakpoint *brk) { memcpy(this_cpu_ptr(¤t_brk[nr]), brk, sizeof(*brk));