diff options
Diffstat (limited to 'arch/x86/kernel/ioport.c')
| -rw-r--r-- | arch/x86/kernel/ioport.c | 47 |
1 files changed, 11 insertions, 36 deletions
diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c index 9ed9458e02df..d5dcde972c42 100644 --- a/arch/x86/kernel/ioport.c +++ b/arch/x86/kernel/ioport.c @@ -153,28 +153,23 @@ SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on) /* * The sys_iopl functionality depends on the level argument, which if - * granted for the task is used by the CPU to check I/O instruction and - * CLI/STI against the current priviledge level (CPL). If CPL is less than - * or equal the tasks IOPL level the instructions take effect. If not a #GP - * is raised. The default IOPL is 0, i.e. no permissions. + * granted for the task is used to enable access to all 65536 I/O ports. * - * Setting IOPL to level 0-2 is disabling the userspace access. Only level - * 3 enables it. If set it allows the user space thread: + * This does not use the IOPL mechanism provided by the CPU as that would + * also allow the user space task to use the CLI/STI instructions. * - * - Unrestricted access to all 65535 I/O ports - * - The usage of CLI/STI instructions + * Disabling interrupts in a user space task is dangerous as it might lock + * up the machine and the semantics vs. syscalls and exceptions is + * undefined. * - * The advantage over ioperm is that the context switch does not require to - * update the I/O bitmap which is especially true when a large number of - * ports is accessed. But the allowance of CLI/STI in userspace is - * considered a major problem. + * Setting IOPL to level 0-2 is disabling I/O permissions. Level 3 + * 3 enables them. * * IOPL is strictly per thread and inherited on fork. */ SYSCALL_DEFINE1(iopl, unsigned int, level) { struct thread_struct *t = ¤t->thread; - struct pt_regs *regs = current_pt_regs(); unsigned int old; /* @@ -187,10 +182,7 @@ SYSCALL_DEFINE1(iopl, unsigned int, level) if (level > 3) return -EINVAL; - if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) - old = t->iopl_emul; - else - old = t->iopl >> X86_EFLAGS_IOPL_BIT; + old = t->iopl_emul; /* No point in going further if nothing changes */ if (level == old) @@ -203,25 +195,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, level) return -EPERM; } - if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) { - t->iopl_emul = level; - task_update_io_bitmap(); - } else { - /* - * Change the flags value on the return stack, which has - * been set up on system-call entry. See also the fork and - * signal handling code how this is handled. - */ - regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | - (level << X86_EFLAGS_IOPL_BIT); - /* Store the new level in the thread struct */ - t->iopl = level << X86_EFLAGS_IOPL_BIT; - /* - * X86_32 switches immediately and XEN handles it via - * emulation. - */ - set_iopl_mask(t->iopl); - } + t->iopl_emul = level; + task_update_io_bitmap(); return 0; } |