um: remove process stub VMA

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>

1 files changed, 0 insertions, 87 deletions

diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index d9961163da66..125df465e8ea 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -14,47 +14,6 @@
 #include <os.h>
 #include <skas.h>
 
-static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
-			 unsigned long kernel)
-{
-	pgd_t *pgd;
-	p4d_t *p4d;
-	pud_t *pud;
-	pmd_t *pmd;
-	pte_t *pte;
-
-	pgd = pgd_offset(mm, proc);
-
-	p4d = p4d_alloc(mm, pgd, proc);
-	if (!p4d)
-		goto out;
-
-	pud = pud_alloc(mm, p4d, proc);
-	if (!pud)
-		goto out_pud;
-
-	pmd = pmd_alloc(mm, pud, proc);
-	if (!pmd)
-		goto out_pmd;
-
-	pte = pte_alloc_map(mm, pmd, proc);
-	if (!pte)
-		goto out_pte;
-
-	*pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
-	*pte = pte_mkread(*pte);
-	return 0;
-
- out_pte:
-	pmd_free(mm, pmd);
- out_pmd:
-	pud_free(mm, pud);
- out_pud:
-	p4d_free(mm, p4d);
- out:
-	return -ENOMEM;
-}
-
 int init_new_context(struct task_struct *task, struct mm_struct *mm)
 {
  	struct mm_context *from_mm = NULL;
@@ -98,52 +57,6 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
 	return ret;
 }
 
-void uml_setup_stubs(struct mm_struct *mm)
-{
-	int err, ret;
-
-	ret = init_stub_pte(mm, STUB_CODE,
-			    (unsigned long) __syscall_stub_start);
-	if (ret)
-		goto out;
-
-	ret = init_stub_pte(mm, STUB_DATA, mm->context.id.stack);
-	if (ret)
-		goto out;
-
-	mm->context.stub_pages[0] = virt_to_page(__syscall_stub_start);
-	mm->context.stub_pages[1] = virt_to_page(mm->context.id.stack);
-
-	/* dup_mmap already holds mmap_lock */
-	err = install_special_mapping(mm, STUB_START, STUB_END - STUB_START,
-				      VM_READ | VM_MAYREAD | VM_EXEC |
-				      VM_MAYEXEC | VM_DONTCOPY | VM_PFNMAP,
-				      mm->context.stub_pages);
-	if (err) {
-		printk(KERN_ERR "install_special_mapping returned %d\n", err);
-		goto out;
-	}
-	return;
-
-out:
-	force_sigsegv(SIGSEGV);
-}
-
-void arch_exit_mmap(struct mm_struct *mm)
-{
-	pte_t *pte;
-
-	pte = virt_to_pte(mm, STUB_CODE);
-	if (pte != NULL)
-		pte_clear(mm, STUB_CODE, pte);
-
-	pte = virt_to_pte(mm, STUB_DATA);
-	if (pte == NULL)
-		return;
-
-	pte_clear(mm, STUB_DATA, pte);
-}
-
 void destroy_context(struct mm_struct *mm)
 {
 	struct mm_context *mmu = &mm->context;