linux_kernel/arch/x86/include/asm/desc.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_DESC_H
#define _ASM_X86_DESC_H

#include <asm/desc_defs.h>
#include <asm/ldt.h>
#include <asm/mmu.h>
#include <asm/fixmap.h>
#include <asm/irq_vectors.h>
#include <asm/cpu_entry_area.h>

#include <linux/smp.h>
#include <linux/percpu.h>

static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *info)
{
	desc->limit0		= info->limit & 0x0ffff;

	desc->base0		= (info->base_addr & 0x0000ffff);
	desc->base1		= (info->base_addr & 0x00ff0000) >> 16;

	desc->type		= (info->read_exec_only ^ 1) << 1;
	desc->type	       |= info->contents << 2;
	/* Set the ACCESS bit so it can be mapped RO */
	desc->type	       |= 1;

	desc->s			= 1;
	desc->dpl		= 0x3;
	desc->p			= info->seg_not_present ^ 1;
	desc->limit1		= (info->limit & 0xf0000) >> 16;
	desc->avl		= info->useable;
	desc->d			= info->seg_32bit;
	desc->g			= info->limit_in_pages;

	desc->base2		= (info->base_addr & 0xff000000) >> 24;
	/*
	 * Don't allow setting of the lm bit. It would confuse
	 * user_64bit_mode and would get overridden by sysret anyway.
	 */
	desc->l			= 0;
}

extern struct desc_ptr idt_descr;
extern gate_desc idt_table[];
extern const struct desc_ptr debug_idt_descr;
extern gate_desc debug_idt_table[];

struct gdt_page {
	struct desc_struct gdt[GDT_ENTRIES];
} __attribute__((aligned(PAGE_SIZE)));

DECLARE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page);

/* Provide the original GDT */
static inline struct desc_struct *get_cpu_gdt_rw(unsigned int cpu)
{
	return per_cpu(gdt_page, cpu).gdt;
}

/* Provide the current original GDT */
static inline struct desc_struct *get_current_gdt_rw(void)
{
	return this_cpu_ptr(&gdt_page)->gdt;
}

/* Provide the fixmap address of the remapped GDT */
static inline struct desc_struct *get_cpu_gdt_ro(int cpu)
{
	return (struct desc_struct *)&get_cpu_entry_area(cpu)->gdt;
}

/* Provide the current read-only GDT */
static inline struct desc_struct *get_current_gdt_ro(void)
{
	return get_cpu_gdt_ro(smp_processor_id());
}

/* Provide the physical address of the GDT page. */
static inline phys_addr_t get_cpu_gdt_paddr(unsigned int cpu)
{
	return per_cpu_ptr_to_phys(get_cpu_gdt_rw(cpu));
}

static inline void pack_gate(gate_desc *gate, unsigned type, unsigned long func,
			     unsigned dpl, unsigned ist, unsigned seg)
{
	gate->offset_low	= (u16) func;
	gate->bits.p		= 1;
	gate->bits.dpl		= dpl;
	gate->bits.zero		= 0;
	gate->bits.type		= type;
	gate->offset_middle	= (u16) (func >> 16);
#ifdef CONFIG_X86_64
	gate->segment		= __KERNEL_CS;
	gate->bits.ist		= ist;
	gate->reserved		= 0;
	gate->offset_high	= (u32) (func >> 32);
#else
	gate->segment		= seg;
	gate->bits.ist		= 0;
#endif
}

static inline int desc_empty(const void *ptr)
{
	const u32 *desc = ptr;

	return !(desc[0] | desc[1]);
}

#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#else
#define load_TR_desc()				native_load_tr_desc()
#define load_gdt(dtr)				native_load_gdt(dtr)
#define load_idt(dtr)				native_load_idt(dtr)
#define load_tr(tr)				asm volatile("ltr %0"::"m" (tr))
#define load_ldt(ldt)				asm volatile("lldt %0"::"m" (ldt))

#define store_gdt(dtr)				native_store_gdt(dtr)
#define store_tr(tr)				(tr = native_store_tr())

#define load_TLS(t, cpu)			native_load_tls(t, cpu)
#define set_ldt					native_set_ldt

#define write_ldt_entry(dt, entry, desc)	native_write_ldt_entry(dt, entry, desc)
#define write_gdt_entry(dt, entry, desc, type)	native_write_gdt_entry(dt, entry, desc, type)
#define write_idt_entry(dt, entry, g)		native_write_idt_entry(dt, entry, g)

static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
{
}

static inline void paravirt_free_ldt(struct desc_struct *ldt, unsigned entries)
{
}
#endif	/* CONFIG_PARAVIRT */

#define store_ldt(ldt) asm("sldt %0" : "=m"(ldt))

static inline void native_write_idt_entry(gate_desc *idt, int entry, const gate_desc *gate)
{
	memcpy(&idt[entry], gate, sizeof(*gate));
}

static inline void native_write_ldt_entry(struct desc_struct *ldt, int entry, const void *desc)
{
	memcpy(&ldt[entry], desc, 8);
}

static inline void
native_write_gdt_entry(struct desc_struct *gdt, int entry, const void *desc, int type)
{
	unsigned int size;

	switch (type) {
	case DESC_TSS:	size = sizeof(tss_desc);	break;
	case DESC_LDT:	size = sizeof(ldt_desc);	break;
	default:	size = sizeof(*gdt);		break;
	}

	memcpy(&gdt[entry], desc, size);
}

static inline void set_tssldt_descriptor(void *d, unsigned long addr,
					 unsigned type, unsigned size)
{
	struct ldttss_desc *desc = d;

	memset(desc, 0, sizeof(*desc));

	desc->limit0		= (u16) size;
	desc->base0		= (u16) addr;
	desc->base1		= (addr >> 16) & 0xFF;
	desc->type		= type;
	desc->p			= 1;
	desc->limit1		= (size >> 16) & 0xF;
	desc->base2		= (addr >> 24) & 0xFF;
#ifdef CONFIG_X86_64
	desc->base3		= (u32) (addr >> 32);
#endif
}

static inline void __set_tss_desc(unsigned cpu, unsigned int entry, struct x86_hw_tss *addr)
{
	struct desc_struct *d = get_cpu_gdt_rw(cpu);
	tss_desc tss;

	set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS,
			      __KERNEL_TSS_LIMIT);
	write_gdt_entry(d, entry, &tss, DESC_TSS);
}

#define set_tss_desc(cpu, addr) __set_tss_desc(cpu, GDT_ENTRY_TSS, addr)

static inline void native_set_ldt(const void *addr, unsigned int entries)
{
	if (likely(entries == 0))
		asm volatile("lldt %w0"::"q" (0));
	else {
		unsigned cpu = smp_processor_id();
		ldt_desc ldt;

		set_tssldt_descriptor(&ldt, (unsigned long)addr, DESC_LDT,
				      entries * LDT_ENTRY_SIZE - 1);
		write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_LDT,
				&ldt, DESC_LDT);
		asm volatile("lldt %w0"::"q" (GDT_ENTRY_LDT*8));
	}
}

static inline void native_load_gdt(const struct desc_ptr *dtr)
{
	asm volatile("lgdt %0"::"m" (*dtr));
}

static inline void native_load_idt(const struct desc_ptr *dtr)
{
	asm volatile("lidt %0"::"m" (*dtr));
}

static inline void native_store_gdt(struct desc_ptr *dtr)
{
	asm volatile("sgdt %0":"=m" (*dtr));
}

static inline void store_idt(struct desc_ptr *dtr)
{
	asm volatile("sidt %0":"=m" (*dtr));
}

/*
 * The LTR instruction marks the TSS GDT entry as busy. On 64-bit, the GDT is
 * a read-only remapping. To prevent a page fault, the GDT is switched to the
 * original writeable version when needed.
 */
#ifdef CONFIG_X86_64
static inline void native_load_tr_desc(void)
{
	struct desc_ptr gdt;
	int cpu = raw_smp_processor_id();
	bool restore = 0;
	struct desc_struct *fixmap_gdt;

	native_store_gdt(&gdt);
	fixmap_gdt = get_cpu_gdt_ro(cpu);

	/*
	 * If the current GDT is the read-only fixmap, swap to the original
	 * writeable version. Swap back at the end.
	 */
	if (gdt.address == (unsigned long)fixmap_gdt) {
		load_direct_gdt(cpu);
		restore = 1;
	}
	asm volatile("ltr %w0"::"q" (GDT_ENTRY_TSS*8));
	if (restore)
		load_fixmap_gdt(cpu);
}
#else
static inline void native_load_tr_desc(void)
{
	asm volatile("ltr %w0"::"q" (GDT_ENTRY_TSS*8));
}
#endif

static inline unsigned long native_store_tr(void)
{
	unsigned long tr;

	asm volatile("str %0":"=r" (tr));

	return tr;
}

static inline void native_load_tls(struct thread_struct *t, unsigned int cpu)
{
	struct desc_struct *gdt = get_cpu_gdt_rw(cpu);
	unsigned int i;

	for (i = 0; i < GDT_ENTRY_TLS_ENTRIES; i++)
		gdt[GDT_ENTRY_TLS_MIN + i] = t->tls_array[i];
}

DECLARE_PER_CPU(bool, __tss_limit_invalid);

static inline void force_reload_TR(void)
{
	struct desc_struct *d = get_current_gdt_rw();
	tss_desc tss;

	memcpy(&tss, &d[GDT_ENTRY_TSS], sizeof(tss_desc));

	/*
	 * LTR requires an available TSS, and the TSS is currently
	 * busy.  Make it be available so that LTR will work.
	 */
	tss.type = DESC_TSS;
	write_gdt_entry(d, GDT_ENTRY_TSS, &tss, DESC_TSS);

	load_TR_desc();
	this_cpu_write(__tss_limit_invalid, false);
}

/*
 * Call this if you need the TSS limit to be correct, which should be the case
 * if and only if you have TIF_IO_BITMAP set or you're switching to a task
 * with TIF_IO_BITMAP set.
 */
static inline void refresh_tss_limit(void)
{
	DEBUG_LOCKS_WARN_ON(preemptible());

	if (unlikely(this_cpu_read(__tss_limit_invalid)))
		force_reload_TR();
}

/*
 * If you do something evil that corrupts the cached TSS limit (I'm looking
 * at you, VMX exits), call this function.
 *
 * The optimization here is that the TSS limit only matters for Linux if the
 * IO bitmap is in use.  If the TSS limit gets forced to its minimum value,
 * everything works except that IO bitmap will be ignored and all CPL 3 IO
 * instructions will #GP, which is exactly what we want for normal tasks.
 */
static inline void invalidate_tss_limit(void)
{
	DEBUG_LOCKS_WARN_ON(preemptible());

	if (unlikely(test_thread_flag(TIF_IO_BITMAP)))
		force_reload_TR();
	else
		this_cpu_write(__tss_limit_invalid, true);
}

/* This intentionally ignores lm, since 32-bit apps don't have that field. */
#define LDT_empty(info)					\
	((info)->base_addr		== 0	&&	\
	 (info)->limit			== 0	&&	\
	 (info)->contents		== 0	&&	\
	 (info)->read_exec_only		== 1	&&	\
	 (info)->seg_32bit		== 0	&&	\
	 (info)->limit_in_pages		== 0	&&	\
	 (info)->seg_not_present	== 1	&&	\
	 (info)->useable		== 0)

/* Lots of programs expect an all-zero user_desc to mean "no segment at all". */
static inline bool LDT_zero(const struct user_desc *info)
{
	return (info->base_addr		== 0 &&
		info->limit		== 0 &&
		info->contents		== 0 &&
		info->read_exec_only	== 0 &&
		info->seg_32bit		== 0 &&
		info->limit_in_pages	== 0 &&
		info->seg_not_present	== 0 &&
		info->useable		== 0);
}

static inline void clear_LDT(void)
{
	set_ldt(NULL, 0);
}

static inline unsigned long get_desc_base(const struct desc_struct *desc)
{
	return (unsigned)(desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24));
}

static inline void set_desc_base(struct desc_struct *desc, unsigned long base)
{
	desc->base0 = base & 0xffff;
	desc->base1 = (base >> 16) & 0xff;
	desc->base2 = (base >> 24) & 0xff;
}

static inline unsigned long get_desc_limit(const struct desc_struct *desc)
{
	return desc->limit0 | (desc->limit1 << 16);
}

static inline void set_desc_limit(struct desc_struct *desc, unsigned long limit)
{
	desc->limit0 = limit & 0xffff;
	desc->limit1 = (limit >> 16) & 0xf;
}

void update_intr_gate(unsigned int n, const void *addr);
void alloc_intr_gate(unsigned int n, const void *addr);

extern unsigned long system_vectors[];

#ifdef CONFIG_X86_64
DECLARE_PER_CPU(u32, debug_idt_ctr);
static inline bool is_debug_idt_enabled(void)
{
	if (this_cpu_read(debug_idt_ctr))
		return true;

	return false;
}

static inline void load_debug_idt(void)
{
	load_idt((const struct desc_ptr *)&debug_idt_descr);
}
#else
static inline bool is_debug_idt_enabled(void)
{
	return false;
}

static inline void load_debug_idt(void)
{
}
#endif

/*
 * The load_current_idt() must be called with interrupts disabled
 * to avoid races. That way the IDT will always be set back to the expected
 * descriptor. It's also called when a CPU is being initialized, and
 * that doesn't need to disable interrupts, as nothing should be
 * bothering the CPU then.
 */
static inline void load_current_idt(void)
{
	if (is_debug_idt_enabled())
		load_debug_idt();
	else
		load_idt((const struct desc_ptr *)&idt_descr);
}

extern void idt_setup_early_handler(void);
extern void idt_setup_early_traps(void);
extern void idt_setup_traps(void);
extern void idt_setup_apic_and_irq_gates(void);

#ifdef CONFIG_X86_64
extern void idt_setup_early_pf(void);
extern void idt_setup_ist_traps(void);
extern void idt_setup_debugidt_traps(void);
#else
static inline void idt_setup_early_pf(void) { }
static inline void idt_setup_ist_traps(void) { }
static inline void idt_setup_debugidt_traps(void) { }
#endif

extern void idt_invalidate(void *addr);

#endif /* _ASM_X86_DESC_H */