This is a note to let you know that I've just added the patch titled
s390/mm: fix fault handling for page table walk case
to the 3.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
s390-mm-fix-fault-handling-for-page-table-walk-case.patch
and it can be found in the queue-3.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 008c2e8f247f0a8db1e8e26139da12f3a3abcda0 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <[email protected]>
Date: Fri, 27 Jul 2012 09:45:39 +0200
Subject: s390/mm: fix fault handling for page table walk case
From: Heiko Carstens <[email protected]>
commit 008c2e8f247f0a8db1e8e26139da12f3a3abcda0 upstream.
Make sure the kernel does not incorrectly create a SIGBUS signal during
user space accesses:
For user space accesses in the switched addressing mode case the kernel
may walk page tables and access user address space via the kernel
mapping. If a page table entry is invalid the function __handle_fault()
gets called in order to emulate a page fault and trigger all the usual
actions like paging in a missing page etc. by calling handle_mm_fault().
If handle_mm_fault() returns with an error fixup handling is necessary.
For the switched addressing mode case all errors need to be mapped to
-EFAULT, so that the calling uaccess function can return -EFAULT to
user space.
Unfortunately the __handle_fault() incorrectly calls do_sigbus() if
VM_FAULT_SIGBUS is set. This however should only happen if a page fault
was triggered by a user space instruction. For kernel mode uaccesses
the correct action is to only return -EFAULT.
So user space may incorrectly see SIGBUS signals because of this bug.
For current machines this would only be possible for the switched
addressing mode case in conjunction with futex operations.
Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/s390/mm/fault.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -443,6 +443,7 @@ int __handle_fault(unsigned long uaddr,
struct pt_regs regs;
int access, fault;
+ /* Emulate a uaccess fault from kernel mode. */
regs.psw.mask = psw_kernel_bits | PSW_MASK_DAT | PSW_MASK_MCHECK;
if (!irqs_disabled())
regs.psw.mask |= PSW_MASK_IO | PSW_MASK_EXT;
@@ -452,12 +453,12 @@ int __handle_fault(unsigned long uaddr,
regs.int_parm_long = (uaddr & PAGE_MASK) | 2;
access = write ? VM_WRITE : VM_READ;
fault = do_exception(®s, access);
- if (unlikely(fault)) {
- if (fault & VM_FAULT_OOM)
- return -EFAULT;
- else if (fault & VM_FAULT_SIGBUS)
- do_sigbus(®s);
- }
+ /*
+ * Since the fault happened in kernel mode while performing a uaccess
+ * all we need to do now is emulating a fixup in case "fault" is not
+ * zero.
+ * For the calling uaccess functions this results always in -EFAULT.
+ */
return fault ? -EFAULT : 0;
}
Patches currently in stable-queue which might be from [email protected]
are
queue-3.5/s390-mm-fix-fault-handling-for-page-table-walk-case.patch
queue-3.5/s390-idle-fix-sequence-handling-vs-cpu-hotplug.patch
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