commit: 008c2e8f247f0a8db1e8e26139da12f3a3abcda0 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
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. Cc: [email protected] Signed-off-by: Heiko Carstens <[email protected]> Signed-off-by: Martin Schwidefsky <[email protected]> --- arch/s390/mm/fault.c | 13 +++++++------ 1 files changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index 2a34a1c..dc659da 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -451,6 +451,7 @@ 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; @@ -460,12 +461,12 @@ int __handle_fault(unsigned long uaddr, unsigned long pgm_int_code, int write) 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; } -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
