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Commit a06db751 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds
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pagemap: check permissions and capabilities at open time 

This patchset makes pagemap useable again in the safe way (after row
hammer bug it was made CAP_SYS_ADMIN-only).  This patchset restores access
for non-privileged users but hides PFNs from them.

Also it adds bit 'map-exclusive' which is set if page is mapped only here:
it helps in estimation of working set without exposing pfns and allows to
distinguish CoWed and non-CoWed private anonymous pages.

Second patch removes page-shift bits and completes migration to the new
pagemap format: flags soft-dirty and mmap-exclusive are available only in
the new format.

This patch (of 5):

This patch moves permission checks from pagemap_read() into pagemap_open().

Pointer to mm is saved in file->private_data. This reference pins only
mm_struct itself. /proc/*/mem, maps, smaps already work in the same way.

See http://lkml.kernel.org/r/CA+55aFyKpWrt_Ajzh1rzp_GcwZ4=6Y=kOv8hBz172CFJp6L8Tg@mail.gmail.com



Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: default avatarMark Williamson <mwilliamson@undo-software.com>
Tested-by: default avatarMark Williamson <mwilliamson@undo-software.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b5e3aa0a

fs/proc/task_mmu.c

+28 −20
Original line number Diff line number Diff line
@@ -1229,40 +1229,33 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask, 
static ssize_t pagemap_read(struct file *file, char __user *buf,

			    size_t count, loff_t *ppos)

{

	struct task_struct *task = get_proc_task(file_inode(file));

	struct mm_struct *mm;

	struct mm_struct *mm = file->private_data;

	struct pagemapread pm;

	int ret = -ESRCH;

	struct mm_walk pagemap_walk = {};

	unsigned long src;

	unsigned long svpfn;

	unsigned long start_vaddr;

	unsigned long end_vaddr;

	int copied = 0;

	int ret = 0, copied = 0;



	if (!task)

	if (!mm || !atomic_inc_not_zero(&mm->mm_users))

		goto out;



	ret = -EINVAL;

	/* file position must be aligned */

	if ((*ppos % PM_ENTRY_BYTES) || (count % PM_ENTRY_BYTES))

		goto out_task;

		goto out_mm;



	ret = 0;

	if (!count)

		goto out_task;

		goto out_mm;



	pm.v2 = soft_dirty_cleared;

	pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);

	pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);

	ret = -ENOMEM;

	if (!pm.buffer)

		goto out_task;



	mm = mm_access(task, PTRACE_MODE_READ);

	ret = PTR_ERR(mm);

	if (!mm || IS_ERR(mm))

		goto out_free;

		goto out_mm;



	pagemap_walk.pmd_entry = pagemap_pte_range;

	pagemap_walk.pte_hole = pagemap_pte_hole;
@@ -1275,10 +1268,10 @@ static ssize_t pagemap_read(struct file *file, char __user *buf, 
	src = *ppos;

	svpfn = src / PM_ENTRY_BYTES;

	start_vaddr = svpfn << PAGE_SHIFT;

	end_vaddr = TASK_SIZE_OF(task);

	end_vaddr = mm->task_size;



	/* watch out for wraparound */

	if (svpfn > TASK_SIZE_OF(task) >> PAGE_SHIFT)

	if (svpfn > mm->task_size >> PAGE_SHIFT)

		start_vaddr = end_vaddr;



	/*
@@ -1305,7 +1298,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf, 
		len = min(count, PM_ENTRY_BYTES * pm.pos);

		if (copy_to_user(buf, pm.buffer, len)) {

			ret = -EFAULT;

			goto out_mm;

			goto out_free;

		}

		copied += len;

		buf += len;
@@ -1315,24 +1308,38 @@ static ssize_t pagemap_read(struct file *file, char __user *buf, 
	if (!ret || ret == PM_END_OF_BUFFER)

		ret = copied;



out_mm:

	mmput(mm);

out_free:

	kfree(pm.buffer);

out_task:

	put_task_struct(task);

out_mm:

	mmput(mm);

out:

	return ret;

}



static int pagemap_open(struct inode *inode, struct file *file)

{

	struct mm_struct *mm;



	/* do not disclose physical addresses: attack vector */

	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;

	pr_warn_once("Bits 55-60 of /proc/PID/pagemap entries are about "

			"to stop being page-shift some time soon. See the "

			"linux/Documentation/vm/pagemap.txt for details.\n");



	mm = proc_mem_open(inode, PTRACE_MODE_READ);

	if (IS_ERR(mm))

		return PTR_ERR(mm);

	file->private_data = mm;

	return 0;

}



static int pagemap_release(struct inode *inode, struct file *file)

{

	struct mm_struct *mm = file->private_data;



	if (mm)

		mmdrop(mm);

	return 0;

}
@@ -1340,6 +1347,7 @@ const struct file_operations proc_pagemap_operations = { 
	.llseek		= mem_lseek, /* borrow this */

	.read		= pagemap_read,

	.open		= pagemap_open,

	.release	= pagemap_release,

};

#endif /* CONFIG_PROC_PAGE_MONITOR */