pagemap: hide physical addresses from non-privileged users

commit 1c90308e upstream.

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: ab676b7d ("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>
[bwh: Backported to 3.2:
 - Add the same check in the places where we look up a PFN
 - Add struct pagemapread * parameters where necessary
 - Open-code file_ns_capable()
 - Delete pagemap_open() entirely, as it would always return 0]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/proc/task_mmu.c

@@ -11,6 +11,7 @@
 #include <linux/rmap.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
+#include <linux/security.h>
 
 #include <asm/elf.h>
 #include <asm/uaccess.h>
@@ -606,6 +607,7 @@ const struct file_operations proc_clear_refs_operations = {
 struct pagemapread {
 	int pos, len;		/* units: PM_ENTRY_BYTES, not bytes */
 	u64 *buffer;
+	bool show_pfn;
 };
 
 #define PM_ENTRY_BYTES      sizeof(u64)
@@ -654,14 +656,14 @@ static u64 swap_pte_to_pagemap_entry(pte_t pte)
 	return swp_type(e) | (swp_offset(e) << MAX_SWAPFILES_SHIFT);
 }
 
-static u64 pte_to_pagemap_entry(pte_t pte)
+static u64 pte_to_pagemap_entry(struct pagemapread *pm, pte_t pte)
 {
 	u64 pme = 0;
 	if (is_swap_pte(pte))
 		pme = PM_PFRAME(swap_pte_to_pagemap_entry(pte))
 			| PM_PSHIFT(PAGE_SHIFT) | PM_SWAP;
 	else if (pte_present(pte))
-		pme = PM_PFRAME(pte_pfn(pte))
+		pme = (pm->show_pfn ? PM_PFRAME(pte_pfn(pte)) : 0)
 			| PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT;
 	return pme;
 }
@@ -693,7 +695,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 		if (vma && (vma->vm_start <= addr) &&
 		    !is_vm_hugetlb_page(vma)) {
 			pte = pte_offset_map(pmd, addr);
-			pfn = pte_to_pagemap_entry(*pte);
+			pfn = pte_to_pagemap_entry(pm, *pte);
 			/* unmap before userspace copy */
 			pte_unmap(pte);
 		}
@@ -708,11 +710,11 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 }
 
 #ifdef CONFIG_HUGETLB_PAGE
-static u64 huge_pte_to_pagemap_entry(pte_t pte, int offset)
+static u64 huge_pte_to_pagemap_entry(struct pagemapread *pm, pte_t pte, int offset)
 {
 	u64 pme = 0;
 	if (pte_present(pte))
-		pme = PM_PFRAME(pte_pfn(pte) + offset)
+		pme = (pm->show_pfn ? PM_PFRAME(pte_pfn(pte) + offset) : 0)
 			| PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT;
 	return pme;
 }
@@ -728,7 +730,7 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
 
 	for (; addr != end; addr += PAGE_SIZE) {
 		int offset = (addr & ~hmask) >> PAGE_SHIFT;
-		pfn = huge_pte_to_pagemap_entry(*pte, offset);
+		pfn = huge_pte_to_pagemap_entry(pm, *pte, offset);
 		err = add_to_pagemap(addr, pfn, pm);
 		if (err)
 			return err;
@@ -792,6 +794,10 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 	if (!count)
 		goto out_task;
 
+	/* do not disclose physical addresses: attack vector */
+	pm.show_pfn = !security_capable(&init_user_ns, file->f_cred, 
+					CAP_SYS_ADMIN);
+
 	pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
 	pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);
 	ret = -ENOMEM;
@@ -864,19 +870,9 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 	return ret;
 }
 
-static int pagemap_open(struct inode *inode, struct file *file)
-{
-	/* do not disclose physical addresses to unprivileged
-	   userspace (closes a rowhammer attack vector) */
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
-	return 0;
-}
-
 const struct file_operations proc_pagemap_operations = {
 	.llseek		= mem_lseek, /* borrow this */
 	.read		= pagemap_read,
-	.open		= pagemap_open,
 };
 #endif /* CONFIG_PROC_PAGE_MONITOR */