1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de) 4 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com) 5 */ 6 7 #include <linux/mm.h> 8 #include <linux/sched/signal.h> 9 #include <linux/slab.h> 10 11 #include <asm/pgalloc.h> 12 #include <asm/sections.h> 13 #include <asm/mmu_context.h> 14 #include <as-layout.h> 15 #include <os.h> 16 #include <skas.h> 17 #include <stub-data.h> 18 19 /* Ensure the stub_data struct covers the allocated area */ 20 static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE); 21 22 int init_new_context(struct task_struct *task, struct mm_struct *mm) 23 { 24 struct mm_id *new_id = &mm->context.id; 25 unsigned long stack = 0; 26 int ret = -ENOMEM; 27 28 stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES)); 29 if (stack == 0) 30 goto out; 31 32 new_id->stack = stack; 33 34 block_signals_trace(); 35 new_id->u.pid = start_userspace(stack); 36 unblock_signals_trace(); 37 38 if (new_id->u.pid < 0) { 39 ret = new_id->u.pid; 40 goto out_free; 41 } 42 43 /* 44 * Ensure the new MM is clean and nothing unwanted is mapped. 45 * 46 * TODO: We should clear the memory up to STUB_START to ensure there is 47 * nothing mapped there, i.e. we (currently) have: 48 * 49 * |- user memory -|- unused -|- stub -|- unused -| 50 * ^ TASK_SIZE ^ STUB_START 51 * 52 * Meaning we have two unused areas where we may still have valid 53 * mappings from our internal clone(). That isn't really a problem as 54 * userspace is not going to access them, but it is definitely not 55 * correct. 56 * 57 * However, we are "lucky" and if rseq is configured, then on 32 bit 58 * it will fall into the first empty range while on 64 bit it is going 59 * to use an anonymous mapping in the second range. As such, things 60 * continue to work for now as long as we don't start unmapping these 61 * areas. 62 * 63 * Change this to STUB_START once we have a clean userspace. 64 */ 65 unmap(new_id, 0, TASK_SIZE); 66 67 return 0; 68 69 out_free: 70 if (new_id->stack != 0) 71 free_pages(new_id->stack, ilog2(STUB_DATA_PAGES)); 72 out: 73 return ret; 74 } 75 76 void destroy_context(struct mm_struct *mm) 77 { 78 struct mm_context *mmu = &mm->context; 79 80 /* 81 * If init_new_context wasn't called, this will be 82 * zero, resulting in a kill(0), which will result in the 83 * whole UML suddenly dying. Also, cover negative and 84 * 1 cases, since they shouldn't happen either. 85 */ 86 if (mmu->id.u.pid < 2) { 87 printk(KERN_ERR "corrupt mm_context - pid = %d\n", 88 mmu->id.u.pid); 89 return; 90 } 91 os_kill_ptraced_process(mmu->id.u.pid, 1); 92 93 free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES)); 94 } 95