bfc58e2b98
This mostly reverts the old commit 3963333fe676 ("uml: cover stubs
with a VMA") which had added a VMA to the existing PTEs. However,
there's no real reason to have the PTEs in the first place and the
VMA cannot be 'fixed' in place, which leads to bugs that userspace
could try to unmap them and be forcefully killed, or such. Also,
there's a bit of an ugly hole in userspace's address space.
Simplify all this: just install the stub code/page at the top of
the (inner) address space, i.e. put it just above TASK_SIZE. The
pages are simply hard-coded to be mapped in the userspace process
we use to implement an mm context, and they're out of reach of the
inner mmap/munmap/mprotect etc. since they're above TASK_SIZE.
Getting rid of the VMA also makes vma_merge() no longer hit one of
the VM_WARN_ON()s there because we installed a VMA while the code
assumes the stack VMA is the first one.
It also removes a lockdep warning about mmap_sem usage since we no
longer have uml_setup_stubs() and thus no longer need to do any
manipulation that would require mmap_sem in activate_mm().
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
80 lines
1.7 KiB
C
80 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
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* Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
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*/
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#include <linux/mm.h>
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#include <linux/sched/signal.h>
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#include <linux/slab.h>
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#include <asm/pgalloc.h>
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#include <asm/sections.h>
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#include <as-layout.h>
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#include <os.h>
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#include <skas.h>
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int init_new_context(struct task_struct *task, struct mm_struct *mm)
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{
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struct mm_context *from_mm = NULL;
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struct mm_context *to_mm = &mm->context;
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unsigned long stack = 0;
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int ret = -ENOMEM;
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stack = get_zeroed_page(GFP_KERNEL);
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if (stack == 0)
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goto out;
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to_mm->id.stack = stack;
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if (current->mm != NULL && current->mm != &init_mm)
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from_mm = ¤t->mm->context;
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block_signals_trace();
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if (from_mm)
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to_mm->id.u.pid = copy_context_skas0(stack,
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from_mm->id.u.pid);
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else to_mm->id.u.pid = start_userspace(stack);
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unblock_signals_trace();
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if (to_mm->id.u.pid < 0) {
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ret = to_mm->id.u.pid;
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goto out_free;
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}
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ret = init_new_ldt(to_mm, from_mm);
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if (ret < 0) {
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printk(KERN_ERR "init_new_context_skas - init_ldt"
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" failed, errno = %d\n", ret);
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goto out_free;
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}
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return 0;
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out_free:
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if (to_mm->id.stack != 0)
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free_page(to_mm->id.stack);
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out:
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return ret;
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}
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void destroy_context(struct mm_struct *mm)
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{
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struct mm_context *mmu = &mm->context;
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/*
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* If init_new_context wasn't called, this will be
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* zero, resulting in a kill(0), which will result in the
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* whole UML suddenly dying. Also, cover negative and
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* 1 cases, since they shouldn't happen either.
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*/
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if (mmu->id.u.pid < 2) {
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printk(KERN_ERR "corrupt mm_context - pid = %d\n",
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mmu->id.u.pid);
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return;
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}
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os_kill_ptraced_process(mmu->id.u.pid, 1);
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free_page(mmu->id.stack);
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free_ldt(mmu);
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}
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