This is a note to let you know that I have just added a patch titled
x86/mm: Fix vmalloc_fault() to handle large pages properly
to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue
This patch is scheduled to be released in version 4.2.8-ckt5.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From f2282ee1b90bbfbbaccbad1945c38611aa2d8810 Mon Sep 17 00:00:00 2001
From: Toshi Kani <toshi.kani@xxxxxxx>
Date: Wed, 17 Feb 2016 18:16:54 -0700
Subject: x86/mm: Fix vmalloc_fault() to handle large pages properly
commit f4eafd8bcd5229e998aa252627703b8462c3b90f upstream.
A kernel page fault oops with the callstack below was observed
when a read syscall was made to a pmem device after a huge amount
(>512GB) of vmalloc ranges was allocated by ioremap() on a x86_64
system:
BUG: unable to handle kernel paging request at ffff880840000ff8
IP: vmalloc_fault+0x1be/0x300
PGD c7f03a067 PUD 0
Oops: 0000 [#1] SM
Call Trace:
__do_page_fault+0x285/0x3e0
do_page_fault+0x2f/0x80
? put_prev_entity+0x35/0x7a0
page_fault+0x28/0x30
? memcpy_erms+0x6/0x10
? schedule+0x35/0x80
? pmem_rw_bytes+0x6a/0x190 [nd_pmem]
? schedule_timeout+0x183/0x240
btt_log_read+0x63/0x140 [nd_btt]
:
? __symbol_put+0x60/0x60
? kernel_read+0x50/0x80
SyS_finit_module+0xb9/0xf0
entry_SYSCALL_64_fastpath+0x1a/0xa4
Since v4.1, ioremap() supports large page (pud/pmd) mappings in
x86_64 and PAE. vmalloc_fault() however assumes that the vmalloc
range is limited to pte mappings.
vmalloc faults do not normally happen in ioremap'd ranges since
ioremap() sets up the kernel page tables, which are shared by
user processes. pgd_ctor() sets the kernel's PGD entries to
user's during fork(). When allocation of the vmalloc ranges
crosses a 512GB boundary, ioremap() allocates a new pud table
and updates the kernel PGD entry to point it. If user process's
PGD entry does not have this update yet, a read/write syscall
to the range will cause a vmalloc fault, which hits the Oops
above as it does not handle a large page properly.
Following changes are made to vmalloc_fault().
64-bit:
- No change for the PGD sync operation as it handles large
pages already.
- Add pud_huge() and pmd_huge() to the validation code to
handle large pages.
- Change pud_page_vaddr() to pud_pfn() since an ioremap range
is not directly mapped (while the if-statement still works
with a bogus addr).
- Change pmd_page() to pmd_pfn() since an ioremap range is not
backed by struct page (while the if-statement still works
with a bogus addr).
32-bit:
- No change for the sync operation since the index3 PGD entry
covers the entire vmalloc range, which is always valid.
(A separate change to sync PGD entry is necessary if this
memory layout is changed regardless of the page size.)
- Add pmd_huge() to the validation code to handle large pages.
This is for completeness since vmalloc_fault() won't happen
in ioremap'd ranges as its PGD entry is always valid.
Reported-by: Henning Schild <henning.schild@xxxxxxxxxxx>
Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Acked-by: Borislav Petkov <bp@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-nvdimm@xxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1455758214-24623-1-git-send-email-toshi.kani@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
arch/x86/mm/fault.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 9dc9098..1d3beaf 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -286,6 +286,9 @@ static noinline int vmalloc_fault(unsigned long address)
if (!pmd_k)
return -1;
+ if (pmd_huge(*pmd_k))
+ return 0;
+
pte_k = pte_offset_kernel(pmd_k, address);
if (!pte_present(*pte_k))
return -1;
@@ -357,8 +360,6 @@ void vmalloc_sync_all(void)
* 64-bit:
*
* Handle a fault on the vmalloc area
- *
- * This assumes no large pages in there.
*/
static noinline int vmalloc_fault(unsigned long address)
{
@@ -400,17 +401,23 @@ static noinline int vmalloc_fault(unsigned long address)
if (pud_none(*pud_ref))
return -1;
- if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
+ if (pud_none(*pud) || pud_pfn(*pud) != pud_pfn(*pud_ref))
BUG();
+ if (pud_huge(*pud))
+ return 0;
+
pmd = pmd_offset(pud, address);
pmd_ref = pmd_offset(pud_ref, address);
if (pmd_none(*pmd_ref))
return -1;
- if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
+ if (pmd_none(*pmd) || pmd_pfn(*pmd) != pmd_pfn(*pmd_ref))
BUG();
+ if (pmd_huge(*pmd))
+ return 0;
+
pte_ref = pte_offset_kernel(pmd_ref, address);
if (!pte_present(*pte_ref))
return -1;
--
2.7.0
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