mmu.c

  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 */
 21static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
 22
 23static spinlock_t mm_list_lock;
 24static struct list_head mm_list;
 25
 26void enter_turnstile(struct mm_id *mm_id) __acquires(turnstile)
 27{
 28	struct mm_context *ctx = container_of(mm_id, struct mm_context, id);
 29
 30	mutex_lock(&ctx->turnstile);
 31}
 32
 33void exit_turnstile(struct mm_id *mm_id) __releases(turnstile)
 34{
 35	struct mm_context *ctx = container_of(mm_id, struct mm_context, id);
 36
 37	mutex_unlock(&ctx->turnstile);
 38}
 39
 40int init_new_context(struct task_struct *task, struct mm_struct *mm)
 41{
 42	struct mm_id *new_id = &mm->context.id;
 43	unsigned long stack = 0;
 44	int ret = -ENOMEM;
 45
 46	mutex_init(&mm->context.turnstile);
 47	spin_lock_init(&mm->context.sync_tlb_lock);
 48
 49	stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
 50	if (stack == 0)
 51		goto out;
 52
 53	new_id->stack = stack;
 54	new_id->syscall_data_len = 0;
 55	new_id->syscall_fd_num = 0;
 56
 57	scoped_guard(spinlock_irqsave, &mm_list_lock) {
 58		/* Insert into list, used for lookups when the child dies */
 59		list_add(&mm->context.list, &mm_list);
 60	}
 61
 62	ret = start_userspace(new_id);
 63	if (ret < 0)
 64		goto out_free;
 65
 66	/* Ensure the new MM is clean and nothing unwanted is mapped */
 67	unmap(new_id, 0, STUB_START);
 68
 69	return 0;
 70
 71 out_free:
 72	free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
 73 out:
 74	return ret;
 75}
 76
 77void destroy_context(struct mm_struct *mm)
 78{
 79	struct mm_context *mmu = &mm->context;
 80
 81	/*
 82	 * If init_new_context wasn't called, this will be
 83	 * zero, resulting in a kill(0), which will result in the
 84	 * whole UML suddenly dying.  Also, cover negative and
 85	 * 1 cases, since they shouldn't happen either.
 86	 *
 87	 * Negative cases happen if the child died unexpectedly.
 88	 */
 89	if (mmu->id.pid >= 0 && mmu->id.pid < 2) {
 90		printk(KERN_ERR "corrupt mm_context - pid = %d\n",
 91		       mmu->id.pid);
 92		return;
 93	}
 94
 95	scoped_guard(spinlock_irqsave, &mm_list_lock)
 96		list_del(&mm->context.list);
 97
 98	if (mmu->id.pid > 0) {
 99		os_kill_ptraced_process(mmu->id.pid, 1);
100		mmu->id.pid = -1;
101	}
102
103	if (using_seccomp && mmu->id.sock)
104		os_close_file(mmu->id.sock);
105
106	free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
107}
108
109static irqreturn_t mm_sigchld_irq(int irq, void* dev)
110{
111	struct mm_context *mm_context;
112	pid_t pid;
113
114	guard(spinlock)(&mm_list_lock);
115
116	while ((pid = os_reap_child()) > 0) {
117		/*
118		* A child died, check if we have an MM with the PID. This is
119		* only relevant in SECCOMP mode (as ptrace will fail anyway).
120		*
121		* See wait_stub_done_seccomp for more details.
122		*/
123		list_for_each_entry(mm_context, &mm_list, list) {
124			if (mm_context->id.pid == pid) {
125				struct stub_data *stub_data;
126				printk("Unexpectedly lost MM child! Affected tasks will segfault.");
127
128				/* Marks the MM as dead */
129				mm_context->id.pid = -1;
130
131				stub_data = (void *)mm_context->id.stack;
132				stub_data->futex = FUTEX_IN_KERN;
133#if IS_ENABLED(CONFIG_SMP)
134				os_futex_wake(&stub_data->futex);
135#endif
136
137				/*
138				 * NOTE: Currently executing syscalls by
139				 * affected tasks may finish normally.
140				 */
141				break;
142			}
143		}
144	}
145
146	return IRQ_HANDLED;
147}
148
149static int __init init_child_tracking(void)
150{
151	int err;
152
153	spin_lock_init(&mm_list_lock);
154	INIT_LIST_HEAD(&mm_list);
155
156	err = request_irq(SIGCHLD_IRQ, mm_sigchld_irq, 0, "SIGCHLD", NULL);
157	if (err < 0)
158		panic("Failed to register SIGCHLD IRQ: %d", err);
159
160	return 0;
161}
162early_initcall(init_child_tracking)