[patch 8/9] x86/iopl: Remove legacy IOPL option

Thomas Gleixner
2019-11-06T20:57:17Z

The IOPL emulation via the I/O bitmap is sufficient. Remove the legacy
cruft dealing with the (e)flags based IOPL mechanism.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/Kconfig | 10 ----
arch/x86/include/asm/paravirt.h | 4 -
arch/x86/include/asm/paravirt_types.h | 2
arch/x86/include/asm/processor.h | 26 +---------
arch/x86/include/asm/xen/hypervisor.h | 2
arch/x86/kernel/ioport.c | 84 +++++++++++-----------------------
arch/x86/kernel/paravirt.c | 2
arch/x86/kernel/process_32.c | 9 ---
arch/x86/kernel/process_64.c | 11 ----
arch/x86/xen/enlighten_pv.c | 10 ----
10 files changed, 34 insertions(+), 126 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1269,14 +1269,8 @@ config X86_IOPL_EMULATION

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.
+ ability to disable interrupts from user space which would be
+ granted if the hardware IOPL mechanism would be used.

config X86_IOPL_NONE
bool "IOPL None"
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -294,10 +294,6 @@ static inline void write_idt_entry(gate_
{
PVOP_VCALL3(cpu.write_idt_entry, dt, entry, g);
}
-static inline void set_iopl_mask(unsigned mask)
-{
- PVOP_VCALL1(cpu.set_iopl_mask, mask);
-}

static inline void paravirt_activate_mm(struct mm_struct *prev,
struct mm_struct *next)
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -140,8 +140,6 @@ struct pv_cpu_ops {

void (*load_sp0)(unsigned long sp0);

- void (*set_iopl_mask)(unsigned mask);
-
void (*wbinvd)(void);

/* cpuid emulation, mostly so that caps bits can be disabled */
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -508,10 +508,10 @@ struct thread_struct {
unsigned int io_zerobits_end;

/*
- * IOPL. Priviledge level dependent I/O permission which includes
- * user space CLI/STI when granted.
+ * IOPL. Priviledge level dependent I/O permission which is
+ * emulated via the I/O bitmap to prevent user space from disabling
+ * interrupts.
*/
- unsigned long iopl;
unsigned long iopl_emul;

mm_segment_t addr_limit;
@@ -547,25 +547,6 @@ extern void tss_update_io_bitmap(struct
*/
#define TS_COMPAT 0x0002 /* 32bit syscall active (64BIT)*/

-/*
- * Set IOPL bits in EFLAGS from given mask
- */
-static inline void native_set_iopl_mask(unsigned mask)
-{
-#ifdef CONFIG_X86_32
- unsigned int reg;
-
- asm volatile ("pushfl;"
- "popl %0;"
- "andl %1, %0;"
- "orl %2, %0;"
- "pushl %0;"
- "popfl"
- : "=&r" (reg)
- : "i" (~X86_EFLAGS_IOPL), "r" (mask));
-#endif
-}
-
static inline void
native_load_sp0(unsigned long sp0)
{
@@ -605,7 +586,6 @@ static inline void load_sp0(unsigned lon
native_load_sp0(sp0);
}

-#define set_iopl_mask native_set_iopl_mask
#endif /* CONFIG_PARAVIRT_XXL */

/* Free all resources held by a thread. */
--- a/arch/x86/include/asm/xen/hypervisor.h
+++ b/arch/x86/include/asm/xen/hypervisor.h
@@ -62,6 +62,4 @@ void xen_arch_register_cpu(int num);
void xen_arch_unregister_cpu(int num);
#endif

-extern void xen_set_iopl_mask(unsigned mask);
-
#endif /* _ASM_X86_XEN_HYPERVISOR_H */
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -164,21 +164,17 @@ SYSCALL_DEFINE3(ioperm, unsigned long, f

/*
* 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.
*/
@@ -186,6 +182,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, leve
{
struct thread_struct *t = &current->thread;
struct pt_regs *regs = current_pt_regs();
+ struct tss_struct *tss;
+ unsigned int tss_base;
unsigned int old;

/*
@@ -198,10 +196,7 @@ SYSCALL_DEFINE1(iopl, unsigned int, leve
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)
@@ -214,47 +209,26 @@ SYSCALL_DEFINE1(iopl, unsigned int, leve
return -EPERM;
}

- if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) {
- struct tss_struct *tss;
- unsigned int tss_base;
-
- /* Prevent racing against a task switch */
- preempt_disable();
- tss = this_cpu_ptr(&cpu_tss_rw);
- if (level == 3) {
- /* Grant access to all I/O ports */
- set_thread_flag(TIF_IO_BITMAP);
- tss_base = IO_BITMAP_OFFSET_VALID_ALL;
- } else if (t->io_bitmap_ptr) {
- /* Thread has a I/O bitmap */
- tss_update_io_bitmap(tss, t);
- set_thread_flag(TIF_IO_BITMAP);
- tss_base = IO_BITMAP_OFFSET_VALID_MAP;
- } else {
- /* Take it out of the context switch work burden */
- clear_thread_flag(TIF_IO_BITMAP);
- tss_base = IO_BITMAP_OFFSET_INVALID;
- }
- tss->x86_tss.io_bitmap_base = tss_base;
- t->iopl_emul = level;
- preempt_enable();
-
+ /* Prevent racing against a task switch */
+ preempt_disable();
+ tss = this_cpu_ptr(&cpu_tss_rw);
+ if (level == 3) {
+ /* Grant access to all I/O ports */
+ set_thread_flag(TIF_IO_BITMAP);
+ tss_base = IO_BITMAP_OFFSET_VALID_ALL;
+ } else if (t->io_bitmap_ptr) {
+ /* Thread has a I/O bitmap */
+ tss_update_io_bitmap(tss, t);
+ set_thread_flag(TIF_IO_BITMAP);
+ tss_base = IO_BITMAP_OFFSET_VALID_MAP;
} 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);
+ /* Take it out of the context switch work burden */
+ clear_thread_flag(TIF_IO_BITMAP);
+ tss_base = IO_BITMAP_OFFSET_INVALID;
}
+ tss->x86_tss.io_bitmap_base = tss_base;
+ t->iopl_emul = level;
+ preempt_enable();

return 0;
}
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -341,8 +341,6 @@ struct paravirt_patch_template pv_ops =
.cpu.iret = native_iret,
.cpu.swapgs = native_swapgs,

- .cpu.set_iopl_mask = native_set_iopl_mask,
-
.cpu.start_context_switch = paravirt_nop,
.cpu.end_context_switch = paravirt_nop,

--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -187,15 +187,6 @@ EXPORT_SYMBOL_GPL(start_thread);
*/
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_to_extra(prev_p, next_p);

/*
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -497,17 +497,6 @@ void compat_start_thread(struct pt_regs

switch_to_extra(prev_p, next_p);

-#ifdef CONFIG_XEN_PV
- /*
- * On Xen PV, IOPL bits in pt_regs->flags have no effect, and
- * current_pt_regs()->flags may not match the current task's
- * intended IOPL. We need to switch it manually.
- */
- if (unlikely(static_cpu_has(X86_FEATURE_XENPV) &&
- prev->iopl != next->iopl))
- xen_set_iopl_mask(next->iopl);
-#endif
-
if (static_cpu_has_bug(X86_BUG_SYSRET_SS_ATTRS)) {
/*
* AMD CPUs have a misfeature: SYSRET sets the SS selector but
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -829,15 +829,6 @@ static void xen_load_sp0(unsigned long s
this_cpu_write(cpu_tss_rw.x86_tss.sp0, sp0);
}

-void xen_set_iopl_mask(unsigned mask)
-{
- struct physdev_set_iopl set_iopl;
-
- /* Force the change at ring 0. */
- set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
- HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
-}
-
static void xen_io_delay(void)
{
}
@@ -1047,7 +1038,6 @@ static const struct pv_cpu_ops xen_cpu_o
.write_idt_entry = xen_write_idt_entry,
.load_sp0 = xen_load_sp0,

- .set_iopl_mask = xen_set_iopl_mask,
.io_delay = xen_io_delay,

/* Xen takes care of %gs when switching to usermode for us */