[PATCH v4 4/5] pagemap: hide physical addresses from non-privileged users

Konstantin Khlebnikov
2015-07-14T15:38:32Z

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

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: ab676b7d6fbf ("pagemap: do not leak physical addresses to non-privileged userspace")
Link: http://lkml.kernel.org/r/1425935472-17949-1-git-send-email-kirill@shutemov.name
---
fs/proc/task_mmu.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 040721fa405a..3a5d338ea219 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -937,6 +937,7 @@ 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)
@@ -1013,7 +1014,8 @@ 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))
@@ -1063,8 +1065,9 @@ 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) {
@@ -1073,7 +1076,7 @@ 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);
@@ -1127,8 +1130,9 @@ 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) {
@@ -1137,7 +1141,7 @@ 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++;
}

@@ -1196,6 +1200,9 @@ 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;
@@ -1265,10 +1272,6 @@ 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);