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 <shared/irq_kern.h>
12 #include <asm/pgalloc.h>
13 #include <asm/sections.h>
14 #include <asm/mmu_context.h>
15 #include <as-layout.h>
16 #include <os.h>
17 #include <skas.h>
18 #include <stub-data.h>
19
20 /* Ensure the stub_data struct covers the allocated area */
21 static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
22
23 static spinlock_t mm_list_lock;
24 static struct list_head mm_list;
25
init_new_context(struct task_struct * task,struct mm_struct * mm)26 int init_new_context(struct task_struct *task, struct mm_struct *mm)
27 {
28 struct mm_id *new_id = &mm->context.id;
29 unsigned long stack = 0;
30 int ret = -ENOMEM;
31
32 stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
33 if (stack == 0)
34 goto out;
35
36 new_id->stack = stack;
37
38 scoped_guard(spinlock_irqsave, &mm_list_lock) {
39 /* Insert into list, used for lookups when the child dies */
40 list_add(&mm->context.list, &mm_list);
41 }
42
43 ret = start_userspace(new_id);
44 if (ret < 0)
45 goto out_free;
46
47 /* Ensure the new MM is clean and nothing unwanted is mapped */
48 unmap(new_id, 0, STUB_START);
49
50 return 0;
51
52 out_free:
53 free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
54 out:
55 return ret;
56 }
57
destroy_context(struct mm_struct * mm)58 void destroy_context(struct mm_struct *mm)
59 {
60 struct mm_context *mmu = &mm->context;
61
62 /*
63 * If init_new_context wasn't called, this will be
64 * zero, resulting in a kill(0), which will result in the
65 * whole UML suddenly dying. Also, cover negative and
66 * 1 cases, since they shouldn't happen either.
67 *
68 * Negative cases happen if the child died unexpectedly.
69 */
70 if (mmu->id.pid >= 0 && mmu->id.pid < 2) {
71 printk(KERN_ERR "corrupt mm_context - pid = %d\n",
72 mmu->id.pid);
73 return;
74 }
75
76 if (mmu->id.pid > 0) {
77 os_kill_ptraced_process(mmu->id.pid, 1);
78 mmu->id.pid = -1;
79 }
80
81 if (using_seccomp && mmu->id.sock)
82 os_close_file(mmu->id.sock);
83
84 free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
85
86 guard(spinlock_irqsave)(&mm_list_lock);
87
88 list_del(&mm->context.list);
89 }
90
mm_sigchld_irq(int irq,void * dev)91 static irqreturn_t mm_sigchld_irq(int irq, void* dev)
92 {
93 struct mm_context *mm_context;
94 pid_t pid;
95
96 guard(spinlock)(&mm_list_lock);
97
98 while ((pid = os_reap_child()) > 0) {
99 /*
100 * A child died, check if we have an MM with the PID. This is
101 * only relevant in SECCOMP mode (as ptrace will fail anyway).
102 *
103 * See wait_stub_done_seccomp for more details.
104 */
105 list_for_each_entry(mm_context, &mm_list, list) {
106 if (mm_context->id.pid == pid) {
107 struct stub_data *stub_data;
108 printk("Unexpectedly lost MM child! Affected tasks will segfault.");
109
110 /* Marks the MM as dead */
111 mm_context->id.pid = -1;
112
113 /*
114 * NOTE: If SMP is implemented, a futex_wake
115 * needs to be added here.
116 */
117 stub_data = (void *)mm_context->id.stack;
118 stub_data->futex = FUTEX_IN_KERN;
119
120 /*
121 * NOTE: Currently executing syscalls by
122 * affected tasks may finish normally.
123 */
124 break;
125 }
126 }
127 }
128
129 return IRQ_HANDLED;
130 }
131
init_child_tracking(void)132 static int __init init_child_tracking(void)
133 {
134 int err;
135
136 spin_lock_init(&mm_list_lock);
137 INIT_LIST_HEAD(&mm_list);
138
139 err = request_irq(SIGCHLD_IRQ, mm_sigchld_irq, 0, "SIGCHLD", NULL);
140 if (err < 0)
141 panic("Failed to register SIGCHLD IRQ: %d", err);
142
143 return 0;
144 }
145 early_initcall(init_child_tracking)
146