pagemap: do not leak physical addresses to non-privileged userspace

As pointed by recent post[1] on exploiting DRAM physical imperfection,
/proc/PID/pagemap exposes sensitive information which can be used to do
attacks.

This disallows anybody without CAP_SYS_ADMIN to read the pagemap.

[1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html

[ Eventually we might want to do anything more finegrained, but for now
  this is the simple model.   - Linus ]

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Seaborn <mseaborn@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
static int show_smap(struct seq_file *m, void *v, int is_pid)
{
	struct vm_area_struct *vma = v;
	struct mem_size_stats mss;
	struct mm_walk smaps_walk = {
		.pmd_entry = smaps_pte_range,
		.mm = vma->vm_mm,
		.private = &mss,
	};

	memset(&mss, 0, sizeof mss);
	/* mmap_sem is held in m_start */
	walk_page_vma(vma, &smaps_walk);

	show_map_vma(m, vma, is_pid);

	seq_printf(m,
		   "Size:           %8lu kB\n"
		   "Rss:            %8lu kB\n"
		   "Pss:            %8lu kB\n"
		   "Shared_Clean:   %8lu kB\n"
		   "Shared_Dirty:   %8lu kB\n"
		   "Private_Clean:  %8lu kB\n"
		   "Private_Dirty:  %8lu kB\n"
		   "Referenced:     %8lu kB\n"
		   "Anonymous:      %8lu kB\n"
		   "AnonHugePages:  %8lu kB\n"
		   "Swap:           %8lu kB\n"
		   "KernelPageSize: %8lu kB\n"
		   "MMUPageSize:    %8lu kB\n"
		   "Locked:         %8lu kB\n",
		   (vma->vm_end - vma->vm_start) >> 10,
		   mss.resident >> 10,
		   (unsigned long)(mss.pss >> (10 + PSS_SHIFT)),
		   mss.shared_clean  >> 10,
		   mss.shared_dirty  >> 10,
		   mss.private_clean >> 10,
		   mss.private_dirty >> 10,
		   mss.referenced >> 10,
		   mss.anonymous >> 10,
		   mss.anonymous_thp >> 10,
		   mss.swap >> 10,
		   vma_kernel_pagesize(vma) >> 10,
		   vma_mmu_pagesize(vma) >> 10,
		   (vma->vm_flags & VM_LOCKED) ?
			(unsigned long)(mss.pss >> (10 + PSS_SHIFT)) : 0);

	show_smap_vma_flags(m, vma);
	m_cache_vma(m, vma);
	return 0;
}

static int show_smap(struct seq_file *m, void *v, int is_pid)
{
	struct vm_area_struct *vma = v;
	struct mem_size_stats mss;
	struct mm_walk smaps_walk = {
		.pmd_entry = smaps_pte_range,
		.mm = vma->vm_mm,
		.private = &mss,
	};

	memset(&mss, 0, sizeof mss);
	/* mmap_sem is held in m_start */
	walk_page_vma(vma, &smaps_walk);

	show_map_vma(m, vma, is_pid);

	seq_printf(m,
		   "Size:           %8lu kB\n"
		   "Rss:            %8lu kB\n"
		   "Pss:            %8lu kB\n"
		   "Shared_Clean:   %8lu kB\n"
		   "Shared_Dirty:   %8lu kB\n"
		   "Private_Clean:  %8lu kB\n"
		   "Private_Dirty:  %8lu kB\n"
		   "Referenced:     %8lu kB\n"
		   "Anonymous:      %8lu kB\n"
		   "AnonHugePages:  %8lu kB\n"
		   "Swap:           %8lu kB\n"
		   "KernelPageSize: %8lu kB\n"
		   "MMUPageSize:    %8lu kB\n"
		   "Locked:         %8lu kB\n",
		   (vma->vm_end - vma->vm_start) >> 10,
		   mss.resident >> 10,
		   (unsigned long)(mss.pss >> (10 + PSS_SHIFT)),
		   mss.shared_clean  >> 10,
		   mss.shared_dirty  >> 10,
		   mss.private_clean >> 10,
		   mss.private_dirty >> 10,
		   mss.referenced >> 10,
		   mss.anonymous >> 10,
		   mss.anonymous_thp >> 10,
		   mss.swap >> 10,
		   vma_kernel_pagesize(vma) >> 10,
		   vma_mmu_pagesize(vma) >> 10,
		   (vma->vm_flags & VM_LOCKED) ?
			(unsigned long)(mss.pss >> (10 + PSS_SHIFT)) : 0);

	show_smap_vma_flags(m, vma);
	m_cache_vma(m, vma);
	return 0;
}
