Re: [PATCH v3 3/3] x86: Support compiling out userspace I/O (iopl and ioperm)

From: Kees Cook
Date: Wed Oct 29 2014 - 12:59:32 EST

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On Wed, Oct 29, 2014 at 9:10 AM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote:
> On the vast majority of modern systems, no processes will use the
> userspsace I/O syscalls, iopl and ioperm. Add a new config option,
> CONFIG_X86_IOPORT, to support configuring them out of the kernel
> entirely. Most current systems do not run programs using these
> syscalls, so X86_IOPORT does not depend on EXPERT, though it does still
> default to y.
>
> In addition to saving a significant amount of space, this also reduces
> the size of several major kernel data structures, drops a bit of code
> from several task-related hot paths, and reduces the attack surface of
> the kernel.
>
> All of the task-related code dealing with userspace I/O permissions now
> lives in process-io.h as several new inline functions, which become
> no-ops without CONFIG_X86_IOPORT.
>
> bloat-o-meter results:
>
> add/remove: 0/4 grow/shrink: 4/9 up/down: 83/-9074 (-8991)
> function old new delta
> drop_fpu 80 160 +80
> perf_event_init_task 638 639 +1
> perf_event_exec 192 193 +1
> perf_event_aux 132 133 +1
> test_tsk_thread_flag 10 - -10
> ioperm_active 14 3 -11
> init_task 916 904 -12
> flush_thread 168 149 -19
> cpu_init 364 339 -25
> __drop_fpu 60 - -60
> ioperm_get 92 6 -86
> exit_thread 105 10 -95
> sys_iopl 106 - -106
> copy_thread 364 257 -107
> __switch_to_xtra 234 123 -111
> sys_ioperm 240 - -240
> init_tss 8576 384 -8192
>
> Signed-off-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> ---
> v3: Eliminated several #ifdefs, and in particular almost all #ifdefs in
> .c files, by adding a macro INIT_SET_IOPL_MASK to use in place of
> the initializer for set_iopl_mask, and using __maybe_unused rather
> than wrapping function definitions in #ifdef. Rebased on v3.18-rc1.
> Recomputed bloat-o-meter.
>
> I assume this should go through the x86 tree rather than the tiny tree.
>
> arch/x86/Kconfig | 10 +++++
> arch/x86/include/asm/paravirt.h | 2 +
> arch/x86/include/asm/paravirt_types.h | 5 +++
> arch/x86/include/asm/processor.h | 51 +++++++++++++++++++++----
> arch/x86/include/asm/syscalls.h | 3 ++
> arch/x86/kernel/Makefile | 3 +-
> arch/x86/kernel/cpu/common.c | 12 +-----
> arch/x86/kernel/entry_64.S | 9 +++--
> arch/x86/kernel/paravirt.c | 2 +-
> arch/x86/kernel/process-io.h | 71 +++++++++++++++++++++++++++++++++++
> arch/x86/kernel/process.c | 34 ++---------------
> arch/x86/kernel/process_32.c | 13 ++-----
> arch/x86/kernel/process_64.c | 2 +-
> arch/x86/kernel/ptrace.c | 8 ++++
> arch/x86/xen/enlighten.c | 4 +-
> drivers/tty/vt/vt_ioctl.c | 2 +-
> kernel/sys_ni.c | 5 +++
> 17 files changed, 169 insertions(+), 67 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f2327e8..a7de2eb 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -984,6 +984,16 @@ config X86_ESPFIX64
> def_bool y
> depends on X86_16BIT && X86_64
>
> +config X86_IOPORT
> + bool "iopl and ioperm system calls"
> + default y
> + ---help---
> + This option enables the iopl and ioperm system calls, which allow
> + privileged userspace processes to directly access I/O ports. This
> + is used by software that drives hardware directly from userspace
> + without using a kernel driver. Unless you intend to run such
> + software, you can safely say N here.
> +
> config TOSHIBA
> tristate "Toshiba Laptop support"
> depends on X86_32
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index cd6e161..52d2ec8 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -299,10 +299,12 @@ static inline void write_idt_entry(gate_desc *dt, int entry, const gate_desc *g)
> {
> PVOP_VCALL3(pv_cpu_ops.write_idt_entry, dt, entry, g);
> }
> +#ifdef CONFIG_X86_IOPORT
> static inline void set_iopl_mask(unsigned mask)
> {
> PVOP_VCALL1(pv_cpu_ops.set_iopl_mask, mask);
> }
> +#endif /* CONFIG_X86_IOPORT */
>
> /* The paravirtualized I/O functions */
> static inline void slow_down_io(void)
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index 7549b8b..a22a5d4 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -142,7 +142,12 @@ struct pv_cpu_ops {
>
> void (*load_sp0)(struct tss_struct *tss, struct thread_struct *t);
>
> +#ifdef CONFIG_X86_IOPORT
> void (*set_iopl_mask)(unsigned mask);
> +#define INIT_SET_IOPL_MASK(f) .set_iopl_mask = f,
> +#else
> +#define INIT_SET_IOPL_MASK(f)
> +#endif
>
> void (*wbinvd)(void);
> void (*io_delay)(void);
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 76751cd..6e0b639 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -255,7 +255,11 @@ struct x86_hw_tss {
> /*
> * IO-bitmap sizes:
> */
> +#ifdef CONFIG_X86_IOPORT
> #define IO_BITMAP_BITS 65536
> +#else
> +#define IO_BITMAP_BITS 0
> +#endif
> #define IO_BITMAP_BYTES (IO_BITMAP_BITS/8)
> #define IO_BITMAP_LONGS (IO_BITMAP_BYTES/sizeof(long))
> #define INVALID_IO_BITMAP_OFFSET 0x8000
> @@ -269,6 +273,7 @@ struct tss_struct {
> */
> struct x86_hw_tss x86_tss;
>
> +#ifdef CONFIG_X86_IOPORT
> /*
> * The extra 1 is there because the CPU will access an
> * additional byte beyond the end of the IO permission
> @@ -276,6 +281,7 @@ struct tss_struct {
> * be within the limit.
> */
> unsigned long io_bitmap[IO_BITMAP_LONGS + 1];
> +#endif /* CONFIG_X86_IOPORT */
>
> /*
> * .. and then another 0x100 bytes for the emergency kernel stack:
> @@ -286,6 +292,24 @@ struct tss_struct {
>
> DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, init_tss);
>
> +static inline void init_tss_io(struct tss_struct *t)
> +{
> +#ifdef CONFIG_X86_IOPORT
> + int i;
> +
> + t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
> +
> + /*
> + * <= is required because the CPU will access up to
> + * 8 bits beyond the end of the IO permission bitmap.
> + */
> + for (i = 0; i <= IO_BITMAP_LONGS; i++)
> + t->io_bitmap[i] = ~0UL;
> +#else
> + t->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
> +#endif
> +}
> +
> /*
> * Save the original ist values for checking stack pointers during debugging
> */
> @@ -510,11 +534,13 @@ struct thread_struct {
> unsigned int saved_fs;
> unsigned int saved_gs;
> #endif
> +#ifdef CONFIG_X86_IOPORT
> /* IO permissions: */
> unsigned long *io_bitmap_ptr;
> unsigned long iopl;
> /* Max allowed port in the bitmap, in bytes: */
> unsigned io_bitmap_max;
> +#endif /* CONFIG_X86_IOPORT */
> /*
> * fpu_counter contains the number of consecutive context switches
> * that the FPU is used. If this is over a threshold, the lazy fpu
> @@ -531,7 +557,7 @@ struct thread_struct {
> */
> static inline void native_set_iopl_mask(unsigned mask)
> {
> -#ifdef CONFIG_X86_32
> +#if defined(CONFIG_X86_IOPORT) && defined(CONFIG_X86_32)
> unsigned int reg;
>
> asm volatile ("pushfl;"
> @@ -842,12 +868,8 @@ static inline void spin_lock_prefetch(const void *x)
> #define STACK_TOP TASK_SIZE
> #define STACK_TOP_MAX STACK_TOP
>
> -#define INIT_THREAD { \
> - .sp0 = sizeof(init_stack) + (long)&init_stack, \
> - .vm86_info = NULL, \
> - .sysenter_cs = __KERNEL_CS, \
> - .io_bitmap_ptr = NULL, \
> -}
> +#ifdef CONFIG_X86_IOPORT
> +#define INIT_THREAD_IO .io_bitmap_ptr = NULL,
>
> /*
> * Note that the .io_bitmap member must be extra-big. This is because
> @@ -855,6 +877,19 @@ static inline void spin_lock_prefetch(const void *x)
> * permission bitmap. The extra byte must be all 1 bits, and must
> * be within the limit.
> */
> +#define INIT_TSS_IO .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
> +#else
> +#define INIT_THREAD_IO
> +#define INIT_TSS_IO
> +#endif
> +
> +#define INIT_THREAD { \
> + .sp0 = sizeof(init_stack) + (long)&init_stack, \
> + .vm86_info = NULL, \
> + .sysenter_cs = __KERNEL_CS, \
> + INIT_THREAD_IO \
> +}
> +
> #define INIT_TSS { \
> .x86_tss = { \
> .sp0 = sizeof(init_stack) + (long)&init_stack, \
> @@ -862,7 +897,7 @@ static inline void spin_lock_prefetch(const void *x)
> .ss1 = __KERNEL_CS, \
> .io_bitmap_base = INVALID_IO_BITMAP_OFFSET, \
> }, \
> - .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 }, \
> + INIT_TSS_IO \
> }
>
> extern unsigned long thread_saved_pc(struct task_struct *tsk);
> diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
> index 592a6a6..4db79ea 100644
> --- a/arch/x86/include/asm/syscalls.h
> +++ b/arch/x86/include/asm/syscalls.h
> @@ -16,9 +16,12 @@
> #include <linux/types.h>
>
> /* Common in X86_32 and X86_64 */
> +
> +#ifdef CONFIG_X86_IOPORT
> /* kernel/ioport.c */
> asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
> asmlinkage long sys_iopl(unsigned int);
> +#endif /* CONFIG_X86_IOPORT */
>
> /* kernel/ldt.c */
> asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 8f1e774..84d5fbe 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -20,7 +20,8 @@ CFLAGS_irq.o := -I$(src)/../include/asm/trace
>
> obj-y := process_$(BITS).o signal.o entry_$(BITS).o
> obj-y += traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
> -obj-y += time.o ioport.o ldt.o dumpstack.o nmi.o
> +obj-y += time.o ldt.o dumpstack.o nmi.o
> +obj-$(CONFIG_X86_IOPORT) += ioport.o
> obj-y += setup.o x86_init.o i8259.o irqinit.o jump_label.o
> obj-$(CONFIG_IRQ_WORK) += irq_work.o
> obj-y += probe_roms.o
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 4b4f78c..ae2e8d7 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1297,7 +1297,6 @@ void cpu_init(void)
> struct tss_struct *t;
> unsigned long v;
> int cpu = stack_smp_processor_id();
> - int i;
>
> wait_for_master_cpu(cpu);
>
> @@ -1357,14 +1356,7 @@ void cpu_init(void)
> }
> }
>
> - t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
> -
> - /*
> - * <= is required because the CPU will access up to
> - * 8 bits beyond the end of the IO permission bitmap.
> - */
> - for (i = 0; i <= IO_BITMAP_LONGS; i++)
> - t->io_bitmap[i] = ~0UL;
> + init_tss_io(t);
>
> atomic_inc(&init_mm.mm_count);
> me->active_mm = &init_mm;
> @@ -1419,7 +1411,7 @@ void cpu_init(void)
> load_TR_desc();
> load_LDT(&init_mm.context);
>
> - t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
> + init_tss_io(t);
>
> #ifdef CONFIG_DOUBLEFAULT
> /* Set up doublefault TSS pointer in the GDT */
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index df088bb..1e6a74e0 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -609,6 +609,11 @@ ENTRY(stub_\func)
> END(stub_\func)
> .endm
>
> + FORK_LIKE clone
> + FORK_LIKE fork
> + FORK_LIKE vfork
> +
> +#ifdef CONFIG_X86_IOPORT
> .macro FIXED_FRAME label,func
> ENTRY(\label)
> CFI_STARTPROC
> @@ -621,10 +626,8 @@ ENTRY(\label)
> END(\label)
> .endm
>
> - FORK_LIKE clone
> - FORK_LIKE fork
> - FORK_LIKE vfork
> FIXED_FRAME stub_iopl, sys_iopl
> +#endif /* CONFIG_X86_IOPORT */
>
> ENTRY(ptregscall_common)
> DEFAULT_FRAME 1 8 /* offset 8: return address */
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 548d25f..e7969d4 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -383,7 +383,7 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
> .iret = native_iret,
> .swapgs = native_swapgs,
>
> - .set_iopl_mask = native_set_iopl_mask,
> + INIT_SET_IOPL_MASK(native_set_iopl_mask)
> .io_delay = native_io_delay,
>
> .start_context_switch = paravirt_nop,
> diff --git a/arch/x86/kernel/process-io.h b/arch/x86/kernel/process-io.h
> index d884444..3e773fa 100644
> --- a/arch/x86/kernel/process-io.h
> +++ b/arch/x86/kernel/process-io.h
> @@ -1,9 +1,17 @@
> #ifndef _X86_KERNEL_PROCESS_IO_H
> #define _X86_KERNEL_PROCESS_IO_H
>
> +static inline void clear_thread_io_bitmap(struct task_struct *p)
> +{
> +#ifdef CONFIG_X86_IOPORT
> + p->thread.io_bitmap_ptr = NULL;
> +#endif /* CONFIG_X86_IOPORT */
> +}

Personally, I prefer seeing these kinds of optional functions declared
in a single block rather than having the #ifdefs inside the functions:

#ifdef CONFIG_X86_IOPORT
static inline void clear_thread_io_bitmap(struct task_struct *p)
{
...
}

static inline int copy_io_bitmap(struct task_struct *me,
struct task_struct *p)
{
...
}

...remaining_functions...

#else
static inline void clear_thread_io_bitmap(struct task_struct *p) { }
static inline int copy_io_bitmap(struct task_struct *me,
struct task_struct *p)
{
return 0;
}
...remaining functions...
#endif /* CONFIG_X86_IOPORT */

But this is entirely a style decision, so I leave it up to the x86
maintainers ...

Another nit may be that we should call this CONFIG_SYSCALL_IOPL or
CONFIG_SYSCALL_IOPERM in keeping with the other CONFIG_SYSCALL_*
naming thread? Again, I don't really care strongly beyond really
wanting to use this new feature! :)

Thanks for working on this!

-Kees

> +
> static inline int copy_io_bitmap(struct task_struct *me,
> struct task_struct *p)
> {
> +#ifdef CONFIG_X86_IOPORT
> if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
> p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
> IO_BITMAP_BYTES, GFP_KERNEL);
> @@ -15,8 +23,71 @@ static inline int copy_io_bitmap(struct task_struct *me,
> } else {
> p->thread.io_bitmap_ptr = NULL;
> }
> +#endif /* CONFIG_X86_IOPORT */
>
> return 0;
> }
>
> +static inline void exit_thread_io(struct task_struct *me)
> +{
> +#ifdef CONFIG_X86_IOPORT
> + struct thread_struct *t = &me->thread;
> + unsigned long *bp = t->io_bitmap_ptr;
> +
> + if (bp) {
> + struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
> +
> + t->io_bitmap_ptr = NULL;
> + clear_thread_flag(TIF_IO_BITMAP);
> + /*
> + * Careful, clear this in the TSS too:
> + */
> + memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
> + t->io_bitmap_max = 0;
> + put_cpu();
> + kfree(bp);
> + }
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> +static inline void switch_iopl_mask(struct thread_struct *prev,
> + struct thread_struct *next)
> +{
> +#ifdef CONFIG_X86_IOPORT
> + /*
> + * Restore IOPL if needed. In normal use, the flags restore
> + * in the switch assembly will handle this. But if the kernel
> + * is running virtualized at a non-zero CPL, the popf will
> + * not restore flags, so it must be done in a separate step.
> + */
> + if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
> + set_iopl_mask(next->iopl);
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> +static inline void switch_io_bitmap(struct tss_struct *tss,
> + struct task_struct *prev_p,
> + struct task_struct *next_p)
> +{
> +#ifdef CONFIG_X86_IOPORT
> + struct thread_struct *prev, *next;
> + prev = &prev_p->thread;
> + next = &next_p->thread;
> +
> + if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> + /*
> + * Copy the relevant range of the IO bitmap.
> + * Normally this is 128 bytes or less:
> + */
> + memcpy(tss->io_bitmap, next->io_bitmap_ptr,
> + max(prev->io_bitmap_max, next->io_bitmap_max));
> + } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
> + /*
> + * Clear any possible leftover bits:
> + */
> + memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
> + }
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> #endif /* _X86_KERNEL_PROCESS_IO_H */
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index e127dda..7ac01bf 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -29,6 +29,8 @@
> #include <asm/debugreg.h>
> #include <asm/nmi.h>
>
> +#include "process-io.h"
> +
> /*
> * per-CPU TSS segments. Threads are completely 'soft' on Linux,
> * no more per-task TSS's. The TSS size is kept cacheline-aligned
> @@ -104,23 +106,7 @@ void arch_task_cache_init(void)
> void exit_thread(void)
> {
> struct task_struct *me = current;
> - struct thread_struct *t = &me->thread;
> - unsigned long *bp = t->io_bitmap_ptr;
> -
> - if (bp) {
> - struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
> -
> - t->io_bitmap_ptr = NULL;
> - clear_thread_flag(TIF_IO_BITMAP);
> - /*
> - * Careful, clear this in the TSS too:
> - */
> - memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
> - t->io_bitmap_max = 0;
> - put_cpu();
> - kfree(bp);
> - }
> -
> + exit_thread_io(me);
> drop_fpu(me);
> }
>
> @@ -225,19 +211,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
> hard_enable_TSC();
> }
>
> - if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> - /*
> - * Copy the relevant range of the IO bitmap.
> - * Normally this is 128 bytes or less:
> - */
> - memcpy(tss->io_bitmap, next->io_bitmap_ptr,
> - max(prev->io_bitmap_max, next->io_bitmap_max));
> - } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
> - /*
> - * Clear any possible leftover bits:
> - */
> - memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
> - }
> + switch_io_bitmap(tss, prev_p, next_p);
> propagate_user_return_notify(prev_p, next_p);
> }
>
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 07550ff..3b82293 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -154,7 +154,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
> childregs->orig_ax = -1;
> childregs->cs = __KERNEL_CS | get_kernel_rpl();
> childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
> - p->thread.io_bitmap_ptr = NULL;
> + clear_thread_io_bitmap(p);
> return 0;
> }
> *childregs = *current_pt_regs();
> @@ -165,7 +165,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
> p->thread.ip = (unsigned long) ret_from_fork;
> task_user_gs(p) = get_user_gs(current_pt_regs());
>
> - p->thread.io_bitmap_ptr = NULL;
> + clear_thread_io_bitmap(p);
> tsk = current;
>
> /*
> @@ -265,14 +265,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
> */
> load_TLS(next, cpu);
>
> - /*
> - * Restore IOPL if needed. In normal use, the flags restore
> - * in the switch assembly will handle this. But if the kernel
> - * is running virtualized at a non-zero CPL, the popf will
> - * not restore flags, so it must be done in a separate step.
> - */
> - if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
> - set_iopl_mask(next->iopl);
> + switch_iopl_mask(prev, next);
>
> /*
> * If it were not for PREEMPT_ACTIVE we could guarantee that the
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index b1babb4..d18f3fc 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -164,7 +164,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
> p->thread.sp = (unsigned long) childregs;
> p->thread.usersp = me->thread.usersp;
> set_tsk_thread_flag(p, TIF_FORK);
> - p->thread.io_bitmap_ptr = NULL;
> + clear_thread_io_bitmap(p);
>
> savesegment(gs, p->thread.gsindex);
> p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs;
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index 749b0e4..fdb74a8 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -785,7 +785,11 @@ static int ptrace_set_debugreg(struct task_struct *tsk, int n,
> static int ioperm_active(struct task_struct *target,
> const struct user_regset *regset)
> {
> +#ifdef CONFIG_X86_IOPORT
> return target->thread.io_bitmap_max / regset->size;
> +#else
> + return 0;
> +#endif
> }
>
> static int ioperm_get(struct task_struct *target,
> @@ -793,12 +797,16 @@ static int ioperm_get(struct task_struct *target,
> unsigned int pos, unsigned int count,
> void *kbuf, void __user *ubuf)
> {
> +#ifdef CONFIG_X86_IOPORT
> if (!target->thread.io_bitmap_ptr)
> return -ENXIO;
>
> return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> target->thread.io_bitmap_ptr,
> 0, IO_BITMAP_BYTES);
> +#else
> + return -ENXIO;
> +#endif
> }
>
> /*
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 1a3f044..8ad0778 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -912,7 +912,7 @@ static void xen_load_sp0(struct tss_struct *tss,
> xen_mc_issue(PARAVIRT_LAZY_CPU);
> }
>
> -static void xen_set_iopl_mask(unsigned mask)
> +static void __maybe_unused xen_set_iopl_mask(unsigned mask)
> {
> struct physdev_set_iopl set_iopl;
>
> @@ -1279,7 +1279,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
> .write_idt_entry = xen_write_idt_entry,
> .load_sp0 = xen_load_sp0,
>
> - .set_iopl_mask = xen_set_iopl_mask,
> + INIT_SET_IOPL_MASK(xen_set_iopl_mask)
> .io_delay = xen_io_delay,
>
> /* Xen takes care of %gs when switching to usermode for us */
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 2bd78e2..7c7d405 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -410,7 +410,7 @@ int vt_ioctl(struct tty_struct *tty,
> *
> * XXX: you should never use these, just call ioperm directly..
> */
> -#ifdef CONFIG_X86
> +#ifdef CONFIG_X86_IOPORT
> case KDADDIO:
> case KDDELIO:
> /*
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 02aa418..f3014fe 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -224,3 +224,8 @@ cond_syscall(sys_seccomp);
>
> /* access BPF programs and maps */
> cond_syscall(sys_bpf);
> +
> +/* userspace I/O port access */
> +cond_syscall(stub_iopl);
> +cond_syscall(sys_iopl);
> +cond_syscall(sys_ioperm);
> --
> 2.1.1
>

--
Kees Cook
Chrome OS Security
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