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x86/iopl: Restrict iopl() permission scope

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The access to the full I/O port range can be also provided by the TSS I/O
bitmap, but that would require to copy 8k of data on scheduling in the
task. As shown with the sched out optimization TSS.io_bitmap_base can be
used to switch the incoming task to a preallocated I/O bitmap which has all
bits zero, i.e. allows access to all I/O ports.

Implementing this allows to provide an iopl() emulation mode which restricts
the IOPL level 3 permissions to I/O port access but removes the STI/CLI
permission which is coming with the hardware IOPL mechansim.

Provide a config option to switch IOPL to emulation mode, make it the
default and while at it also provide an option to disable IOPL completely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
This commit is contained in:
Thomas Gleixner 2019-11-11 23:03:28 +01:00
parent be9afb4b52
commit c8137ace56
6 changed files with 137 additions and 45 deletions
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32
arch/x86/Kconfig
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@ -1254,6 +1254,38 @@ config X86_VSYSCALL_EMULATION
Disabling this option saves about 7K of kernel size and
possibly 4K of additional runtime pagetable memory.
choice
prompt "IOPL"
default X86_IOPL_EMULATION
config X86_IOPL_EMULATION
bool "IOPL Emulation"
---help---
Legacy IOPL support is an overbroad mechanism which allows user
space aside of accessing all 65536 I/O ports also to disable
interrupts. To gain this access the caller needs CAP_SYS_RAWIO
capabilities and permission from potentially active security
modules.
The emulation restricts the functionality of the syscall to
only allowing the full range I/O port access, but prevents the
ability to disable interrupts from user space.
config X86_IOPL_LEGACY
bool "IOPL Legacy"
---help---
Allow the full IOPL permissions, i.e. user space access to all
65536 I/O ports and also the ability to disable interrupts, which
is overbroad and can result in system lockups.
config X86_IOPL_NONE
bool "IOPL None"
---help---
Disable the IOPL permission syscall. That's the safest option as
no sane application should depend on this functionality.
endchoice
config TOSHIBA
tristate "Toshiba Laptop support"
depends on X86_32

2
arch/x86/include/asm/pgtable_32_types.h
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@ -44,7 +44,7 @@ extern bool __vmalloc_start_set; /* set once high_memory is set */
* Define this here and validate with BUILD_BUG_ON() in pgtable_32.c
* to avoid include recursion hell
*/
#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 40)
#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 41)
#define CPU_ENTRY_AREA_BASE \
((FIXADDR_TOT_START - PAGE_SIZE * (CPU_ENTRY_AREA_PAGES + 1)) \

28
arch/x86/include/asm/processor.h
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@ -332,19 +332,21 @@ struct x86_hw_tss {
#define IO_BITMAP_BYTES (IO_BITMAP_BITS / BITS_PER_BYTE)
#define IO_BITMAP_LONGS (IO_BITMAP_BYTES / sizeof(long))
#define IO_BITMAP_OFFSET_VALID \
#define IO_BITMAP_OFFSET_VALID_MAP \
(offsetof(struct tss_struct, io_bitmap.bitmap) - \
offsetof(struct tss_struct, x86_tss))
#define IO_BITMAP_OFFSET_VALID_ALL \
(offsetof(struct tss_struct, io_bitmap.mapall) - \
offsetof(struct tss_struct, x86_tss))
/*
* sizeof(unsigned long) coming from an extra "long" at the end
* of the iobitmap.
*
* -1? seg base+limit should be pointing to the address of the
* last valid byte
* sizeof(unsigned long) coming from an extra "long" at the end of the
* iobitmap. The limit is inclusive, i.e. the last valid byte.
*/
#define __KERNEL_TSS_LIMIT \
(IO_BITMAP_OFFSET_VALID + IO_BITMAP_BYTES + sizeof(unsigned long) - 1)
(IO_BITMAP_OFFSET_VALID_ALL + IO_BITMAP_BYTES + \
sizeof(unsigned long) - 1)
/* Base offset outside of TSS_LIMIT so unpriviledged IO causes #GP */
#define IO_BITMAP_OFFSET_INVALID (__KERNEL_TSS_LIMIT + 1)
@ -380,6 +382,12 @@ struct x86_io_bitmap {
* be within the limit.
*/
unsigned long bitmap[IO_BITMAP_LONGS + 1];
/*
* Special I/O bitmap to emulate IOPL(3). All bytes zero,
* except the additional byte at the end.
*/
unsigned long mapall[IO_BITMAP_LONGS + 1];
};
struct tss_struct {
@ -506,7 +514,13 @@ struct thread_struct {
#endif
/* IO permissions: */
struct io_bitmap *io_bitmap;
/*
* IOPL. Priviledge level dependent I/O permission which includes
* user space CLI/STI when granted.
*/
unsigned long iopl;
unsigned long iopl_emul;
mm_segment_t addr_limit;

5
arch/x86/kernel/cpu/common.c
View File

@ -1864,6 +1864,11 @@ void cpu_init(void)
tss->io_bitmap.prev_max = 0;
tss->io_bitmap.prev_sequence = 0;
memset(tss->io_bitmap.bitmap, 0xff, sizeof(tss->io_bitmap.bitmap));
/*
* Invalidate the extra array entry past the end of the all
* permission bitmap as required by the hardware.
*/
tss->io_bitmap.mapall[IO_BITMAP_LONGS] = ~0UL;
set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
load_TR_desc();

87
arch/x86/kernel/ioport.c
View File

@ -17,25 +17,41 @@
static atomic64_t io_bitmap_sequence;
void io_bitmap_share(struct task_struct *tsk)
{
/*
* Take a refcount on current's bitmap. It can be used by
* both tasks as long as none of them changes the bitmap.
*/
refcount_inc(&current->thread.io_bitmap->refcnt);
tsk->thread.io_bitmap = current->thread.io_bitmap;
{
/* Can be NULL when current->thread.iopl_emul == 3 */
if (current->thread.io_bitmap) {
/*
* Take a refcount on current's bitmap. It can be used by
* both tasks as long as none of them changes the bitmap.
*/
refcount_inc(&current->thread.io_bitmap->refcnt);
tsk->thread.io_bitmap = current->thread.io_bitmap;
}
set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
}
static void task_update_io_bitmap(void)
{
struct thread_struct *t = &current->thread;
if (t->iopl_emul == 3 || t->io_bitmap) {
/* TSS update is handled on exit to user space */
set_thread_flag(TIF_IO_BITMAP);
} else {
clear_thread_flag(TIF_IO_BITMAP);
/* Invalidate TSS */
preempt_disable();
tss_update_io_bitmap();
preempt_enable();
}
}
void io_bitmap_exit(void)
{
struct io_bitmap *iobm = current->thread.io_bitmap;
current->thread.io_bitmap = NULL;
clear_thread_flag(TIF_IO_BITMAP);
preempt_disable();
tss_update_io_bitmap();
preempt_enable();
task_update_io_bitmap();
if (iobm && refcount_dec_and_test(&iobm->refcnt))
kfree(iobm);
}
@ -157,36 +173,55 @@ SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
*/
SYSCALL_DEFINE1(iopl, unsigned int, level)
{
struct pt_regs *regs = current_pt_regs();
struct thread_struct *t = &current->thread;
struct pt_regs *regs = current_pt_regs();
unsigned int old;
/*
* Careful: the IOPL bits in regs->flags are undefined under Xen PV
* and changing them has no effect.
*/
unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
if (IS_ENABLED(CONFIG_X86_IOPL_NONE))
return -ENOSYS;
if (level > 3)
return -EINVAL;
if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION))
old = t->iopl_emul;
else
old = t->iopl >> X86_EFLAGS_IOPL_BIT;
/* No point in going further if nothing changes */
if (level == old)
return 0;
/* Trying to gain more privileges? */
if (level > old) {
if (!capable(CAP_SYS_RAWIO) ||
security_locked_down(LOCKDOWN_IOPORT))
return -EPERM;
}
/*
* 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);
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);
}
return 0;
}

28
arch/x86/kernel/process.c
View File

@ -376,21 +376,27 @@ static void tss_copy_io_bitmap(struct tss_struct *tss, struct io_bitmap *iobm)
void tss_update_io_bitmap(void)
{
struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
u16 *base = &tss->x86_tss.io_bitmap_base;
if (test_thread_flag(TIF_IO_BITMAP)) {
struct io_bitmap *iobm = current->thread.io_bitmap;
struct thread_struct *t = &current->thread;
/*
* Only copy bitmap data when the sequence number
* differs. The update time is accounted to the incoming
* task.
*/
if (tss->io_bitmap.prev_sequence != iobm->sequence)
tss_copy_io_bitmap(tss, iobm);
/* Enable the bitmap */
tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION) &&
t->iopl_emul == 3) {
*base = IO_BITMAP_OFFSET_VALID_ALL;
} else {
struct io_bitmap *iobm = t->io_bitmap;
/*
* Only copy bitmap data when the sequence number
* differs. The update time is accounted to the
* incoming task.
*/
if (tss->io_bitmap.prev_sequence != iobm->sequence)
tss_copy_io_bitmap(tss, iobm);
/* Enable the bitmap */
*base = IO_BITMAP_OFFSET_VALID_MAP;
}
/*
* Make sure that the TSS limit is covering the io bitmap.
* It might have been cut down by a VMEXIT to 0x67 which