pagemap: hide physical addresses from non-privileged users

This patch makes pagemap readable for normal users and hides physical
addresses from them.  For some use-cases PFN isn't required at all.

See http://lkml.kernel.org/r/1425935472-17949-1-git-send-email-kirill@shutemov.name

Fixes: ab676b7d6fbf ("pagemap: do not leak physical addresses to non-privileged userspace")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: Mark Williamson <mwilliamson@undo-software.com>
Tested-by:  Mark Williamson <mwilliamson@undo-software.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 98ba9ea..bc65164 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -939,6 +939,7 @@ typedef struct {
 struct pagemapread {
        int pos, len;           /* units: PM_ENTRY_BYTES, not bytes */
        pagemap_entry_t *buffer;
+       bool show_pfn;
 };
 
 #define PAGEMAP_WALK_SIZE      (PMD_SIZE)
@@ -1015,7 +1016,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
        struct page *page = NULL;
 
        if (pte_present(pte)) {
-               frame = pte_pfn(pte);
+               if (pm->show_pfn)
+                       frame = pte_pfn(pte);
                flags |= PM_PRESENT;
                page = vm_normal_page(vma, addr, pte);
                if (pte_soft_dirty(pte))
@@ -1065,8 +1067,9 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
                 */
                if (pmd_present(pmd)) {
                        flags |= PM_PRESENT;
-                       frame = pmd_pfn(pmd) +
-                               ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+                       if (pm->show_pfn)
+                               frame = pmd_pfn(pmd) +
+                                       ((addr & ~PMD_MASK) >> PAGE_SHIFT);
                }
 
                for (; addr != end; addr += PAGE_SIZE) {
@@ -1075,7 +1078,7 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
                        err = add_to_pagemap(addr, &pme, pm);
                        if (err)
                                break;
-                       if (flags & PM_PRESENT)
+                       if (pm->show_pfn && (flags & PM_PRESENT))
                                frame++;
                }
                spin_unlock(ptl);
@@ -1129,8 +1132,9 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask,
                        flags |= PM_FILE;
 
                flags |= PM_PRESENT;
-               frame = pte_pfn(pte) +
-                       ((addr & ~hmask) >> PAGE_SHIFT);
+               if (pm->show_pfn)
+                       frame = pte_pfn(pte) +
+                               ((addr & ~hmask) >> PAGE_SHIFT);
        }
 
        for (; addr != end; addr += PAGE_SIZE) {
@@ -1139,7 +1143,7 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask,
                err = add_to_pagemap(addr, &pme, pm);
                if (err)
                        return err;
-               if (flags & PM_PRESENT)
+               if (pm->show_pfn && (flags & PM_PRESENT))
                        frame++;
        }
 
@@ -1198,6 +1202,9 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
        if (!count)
                goto out_mm;
 
+       /* do not disclose physical addresses: attack vector */
+       pm.show_pfn = file_ns_capable(file, &init_user_ns, CAP_SYS_ADMIN);
+
        pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
        pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);
        ret = -ENOMEM;
@@ -1267,10 +1274,6 @@ 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;
-
        mm = proc_mem_open(inode, PTRACE_MODE_READ);
        if (IS_ERR(mm))
                return PTR_ERR(mm);