[tip:x86/mm] x86/mm/64: Fix crash in remove_pagetable()

[tip-bot for Kirill A. Shutemov]

Commit-ID:  e6ab9c4d437764c7fb728d428dc9e717cdb183d0
Gitweb:     http://git.kernel.org/tip/e6ab9c4d437764c7fb728d428dc9e717cdb183d0
Author:     Kirill A. Shutemov <kirill.shute...@linux.intel.com>
AuthorDate: Tue, 25 Apr 2017 12:25:57 +0300
Committer:  Ingo Molnar <mi...@kernel.org>
CommitDate: Wed, 26 Apr 2017 08:26:43 +0200

x86/mm/64: Fix crash in remove_pagetable()

remove_pagetable() does page walk using p*d_page_vaddr() plus cast.
It's not canonical approach -- we usually use p*d_offset() for that.

It works fine as long as all page table levels are present. We broke the
invariant by introducing folded p4d page table level.

As result, remove_pagetable() interprets PMD as PUD and it leads to
crash:

        BUG: unable to handle kernel paging request at ffff880300000000
        IP: memchr_inv+0x60/0x110
        PGD 317d067
        P4D 317d067
        PUD 3180067
        PMD 33f102067
        PTE 8000000300000060

Let's fix this by using p*d_offset() instead of p*d_page_vaddr() for
page walk.

Reported-by: Dan Williams <dan.j.willi...@intel.com>
Tested-by: Dan Williams <dan.j.willi...@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Dave Hansen <dave.han...@intel.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: linux...@kvack.org
Fixes: f2a6a7050109 ("x86: Convert the rest of the code to support p4d_t")
Link: 
http://lkml.kernel.org/r/20170425092557.21852-1-kirill.shute...@linux.intel.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
 arch/x86/mm/init_64.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a242139..745e5e1 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -962,7 +962,7 @@ remove_pud_table(pud_t *pud_start, unsigned long addr, 
unsigned long end,
                        continue;
                }
 
-               pmd_base = (pmd_t *)pud_page_vaddr(*pud);
+               pmd_base = pmd_offset(pud, 0);
                remove_pmd_table(pmd_base, addr, next, direct);
                free_pmd_table(pmd_base, pud);
        }
@@ -988,7 +988,7 @@ remove_p4d_table(p4d_t *p4d_start, unsigned long addr, 
unsigned long end,
 
                BUILD_BUG_ON(p4d_large(*p4d));
 
-               pud_base = (pud_t *)p4d_page_vaddr(*p4d);
+               pud_base = pud_offset(p4d, 0);
                remove_pud_table(pud_base, addr, next, direct);
                free_pud_table(pud_base, p4d);
        }
@@ -1013,7 +1013,7 @@ remove_pagetable(unsigned long start, unsigned long end, 
bool direct)
                if (!pgd_present(*pgd))
                        continue;
 
-               p4d = (p4d_t *)pgd_page_vaddr(*pgd);
+               p4d = p4d_offset(pgd, 0);
                remove_p4d_table(p4d, addr, next, direct);
        }