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authorHeiko Carstens <heiko.carstens@de.ibm.com>2012-07-27 09:45:39 +0200
committerBen Hutchings <ben@decadent.org.uk>2012-08-10 00:24:58 +0100
commitc929e9bc8cadd3dd1e914498e3905d3d4cc43f85 (patch)
parente551857183b52b1af787e35b25a4e556fa0c0c75 (diff)
s390/mm: fix fault handling for page table walk case
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 <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> [bwh: Backported to 3.2: do_exception() and do_sigbus() parameters differ] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
1 files changed, 7 insertions, 6 deletions
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index b28aaa495d35..0fc0a7e3c0ee 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -453,6 +453,7 @@ int __handle_fault(unsigned long uaddr, unsigned long pgm_int_code, int write)
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;
@@ -461,12 +462,12 @@ int __handle_fault(unsigned long uaddr, unsigned long pgm_int_code, int write)
uaddr &= PAGE_MASK;
access = write ? VM_WRITE : VM_READ;
fault = do_exception(&regs, access, uaddr | 2);
- if (unlikely(fault)) {
- if (fault & VM_FAULT_OOM)
- return -EFAULT;
- else if (fault & VM_FAULT_SIGBUS)
- do_sigbus(&regs, pgm_int_code, uaddr);
- }
+ /*
+ * 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;