LXR linux/arch/x86/include/asm/segment.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _ASM_X86_SEGMENT_H
   3#define _ASM_X86_SEGMENT_H
   4
   5#include <linux/const.h>
   6#include <asm/alternative.h>
   7
   8/*
   9 * Constructor for a conventional segment GDT (or LDT) entry.
  10 * This is a macro so it can be used in initializers.
  11 */
  12#define GDT_ENTRY(flags, base, limit)                   \
  13        ((((base)  & _AC(0xff000000,ULL)) << (56-24)) | \
  14         (((flags) & _AC(0x0000f0ff,ULL)) << 40) |      \
  15         (((limit) & _AC(0x000f0000,ULL)) << (48-16)) | \
  16         (((base)  & _AC(0x00ffffff,ULL)) << 16) |      \
  17         (((limit) & _AC(0x0000ffff,ULL))))
  18
  19/* Simple and small GDT entries for booting only: */
  20
  21#define GDT_ENTRY_BOOT_CS       2
  22#define GDT_ENTRY_BOOT_DS       3
  23#define GDT_ENTRY_BOOT_TSS      4
  24#define __BOOT_CS               (GDT_ENTRY_BOOT_CS*8)
  25#define __BOOT_DS               (GDT_ENTRY_BOOT_DS*8)
  26#define __BOOT_TSS              (GDT_ENTRY_BOOT_TSS*8)
  27
  28/*
  29 * Bottom two bits of selector give the ring
  30 * privilege level
  31 */
  32#define SEGMENT_RPL_MASK        0x3
  33
  34/* User mode is privilege level 3: */
  35#define USER_RPL                0x3
  36
  37/* Bit 2 is Table Indicator (TI): selects between LDT or GDT */
  38#define SEGMENT_TI_MASK         0x4
  39/* LDT segment has TI set ... */
  40#define SEGMENT_LDT             0x4
  41/* ... GDT has it cleared */
  42#define SEGMENT_GDT             0x0
  43
  44#define GDT_ENTRY_INVALID_SEG   0
  45
  46#ifdef CONFIG_X86_32
  47/*
  48 * The layout of the per-CPU GDT under Linux:
  49 *
  50 *   0 - null                                                           <=== cacheline #1
  51 *   1 - reserved
  52 *   2 - reserved
  53 *   3 - reserved
  54 *
  55 *   4 - unused                                                         <=== cacheline #2
  56 *   5 - unused
  57 *
  58 *  ------- start of TLS (Thread-Local Storage) segments:
  59 *
  60 *   6 - TLS segment #1                 [ glibc's TLS segment ]
  61 *   7 - TLS segment #2                 [ Wine's %fs Win32 segment ]
  62 *   8 - TLS segment #3                                                 <=== cacheline #3
  63 *   9 - reserved
  64 *  10 - reserved
  65 *  11 - reserved
  66 *
  67 *  ------- start of kernel segments:
  68 *
  69 *  12 - kernel code segment                                            <=== cacheline #4
  70 *  13 - kernel data segment
  71 *  14 - default user CS
  72 *  15 - default user DS
  73 *  16 - TSS                                                            <=== cacheline #5
  74 *  17 - LDT
  75 *  18 - PNPBIOS support (16->32 gate)
  76 *  19 - PNPBIOS support
  77 *  20 - PNPBIOS support                                                <=== cacheline #6
  78 *  21 - PNPBIOS support
  79 *  22 - PNPBIOS support
  80 *  23 - APM BIOS support
  81 *  24 - APM BIOS support                                               <=== cacheline #7
  82 *  25 - APM BIOS support
  83 *
  84 *  26 - ESPFIX small SS
  85 *  27 - per-cpu                        [ offset to per-cpu data area ]
  86 *  28 - stack_canary-20                [ for stack protector ]         <=== cacheline #8
  87 *  29 - unused
  88 *  30 - unused
  89 *  31 - TSS for double fault handler
  90 */
  91#define GDT_ENTRY_TLS_MIN               6
  92#define GDT_ENTRY_TLS_MAX               (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
  93
  94#define GDT_ENTRY_KERNEL_CS             12
  95#define GDT_ENTRY_KERNEL_DS             13
  96#define GDT_ENTRY_DEFAULT_USER_CS       14
  97#define GDT_ENTRY_DEFAULT_USER_DS       15
  98#define GDT_ENTRY_TSS                   16
  99#define GDT_ENTRY_LDT                   17
 100#define GDT_ENTRY_PNPBIOS_CS32          18
 101#define GDT_ENTRY_PNPBIOS_CS16          19
 102#define GDT_ENTRY_PNPBIOS_DS            20
 103#define GDT_ENTRY_PNPBIOS_TS1           21
 104#define GDT_ENTRY_PNPBIOS_TS2           22
 105#define GDT_ENTRY_APMBIOS_BASE          23
 106
 107#define GDT_ENTRY_ESPFIX_SS             26
 108#define GDT_ENTRY_PERCPU                27
 109#define GDT_ENTRY_STACK_CANARY          28
 110
 111#define GDT_ENTRY_DOUBLEFAULT_TSS       31
 112
 113/*
 114 * Number of entries in the GDT table:
 115 */
 116#define GDT_ENTRIES                     32
 117
 118/*
 119 * Segment selector values corresponding to the above entries:
 120 */
 121
 122#define __KERNEL_CS                     (GDT_ENTRY_KERNEL_CS*8)
 123#define __KERNEL_DS                     (GDT_ENTRY_KERNEL_DS*8)
 124#define __USER_DS                       (GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
 125#define __USER_CS                       (GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
 126#define __ESPFIX_SS                     (GDT_ENTRY_ESPFIX_SS*8)
 127
 128/* segment for calling fn: */
 129#define PNP_CS32                        (GDT_ENTRY_PNPBIOS_CS32*8)
 130/* code segment for BIOS: */
 131#define PNP_CS16                        (GDT_ENTRY_PNPBIOS_CS16*8)
 132
 133/* "Is this PNP code selector (PNP_CS32 or PNP_CS16)?" */
 134#define SEGMENT_IS_PNP_CODE(x)          (((x) & 0xf4) == PNP_CS32)
 135
 136/* data segment for BIOS: */
 137#define PNP_DS                          (GDT_ENTRY_PNPBIOS_DS*8)
 138/* transfer data segment: */
 139#define PNP_TS1                         (GDT_ENTRY_PNPBIOS_TS1*8)
 140/* another data segment: */
 141#define PNP_TS2                         (GDT_ENTRY_PNPBIOS_TS2*8)
 142
 143#ifdef CONFIG_SMP
 144# define __KERNEL_PERCPU                (GDT_ENTRY_PERCPU*8)
 145#else
 146# define __KERNEL_PERCPU                0
 147#endif
 148
 149#ifdef CONFIG_STACKPROTECTOR
 150# define __KERNEL_STACK_CANARY          (GDT_ENTRY_STACK_CANARY*8)
 151#else
 152# define __KERNEL_STACK_CANARY          0
 153#endif
 154
 155#else /* 64-bit: */
 156
 157#include <asm/cache.h>
 158
 159#define GDT_ENTRY_KERNEL32_CS           1
 160#define GDT_ENTRY_KERNEL_CS             2
 161#define GDT_ENTRY_KERNEL_DS             3
 162
 163/*
 164 * We cannot use the same code segment descriptor for user and kernel mode,
 165 * not even in long flat mode, because of different DPL.
 166 *
 167 * GDT layout to get 64-bit SYSCALL/SYSRET support right. SYSRET hardcodes
 168 * selectors:
 169 *
 170 *   if returning to 32-bit userspace: cs = STAR.SYSRET_CS,
 171 *   if returning to 64-bit userspace: cs = STAR.SYSRET_CS+16,
 172 *
 173 * ss = STAR.SYSRET_CS+8 (in either case)
 174 *
 175 * thus USER_DS should be between 32-bit and 64-bit code selectors:
 176 */
 177#define GDT_ENTRY_DEFAULT_USER32_CS     4
 178#define GDT_ENTRY_DEFAULT_USER_DS       5
 179#define GDT_ENTRY_DEFAULT_USER_CS       6
 180
 181/* Needs two entries */
 182#define GDT_ENTRY_TSS                   8
 183/* Needs two entries */
 184#define GDT_ENTRY_LDT                   10
 185
 186#define GDT_ENTRY_TLS_MIN               12
 187#define GDT_ENTRY_TLS_MAX               14
 188
 189/* Abused to load per CPU data from limit */
 190#define GDT_ENTRY_PER_CPU               15
 191
 192/*
 193 * Number of entries in the GDT table:
 194 */
 195#define GDT_ENTRIES                     16
 196
 197/*
 198 * Segment selector values corresponding to the above entries:
 199 *
 200 * Note, selectors also need to have a correct RPL,
 201 * expressed with the +3 value for user-space selectors:
 202 */
 203#define __KERNEL32_CS                   (GDT_ENTRY_KERNEL32_CS*8)
 204#define __KERNEL_CS                     (GDT_ENTRY_KERNEL_CS*8)
 205#define __KERNEL_DS                     (GDT_ENTRY_KERNEL_DS*8)
 206#define __USER32_CS                     (GDT_ENTRY_DEFAULT_USER32_CS*8 + 3)
 207#define __USER_DS                       (GDT_ENTRY_DEFAULT_USER_DS*8 + 3)
 208#define __USER32_DS                     __USER_DS
 209#define __USER_CS                       (GDT_ENTRY_DEFAULT_USER_CS*8 + 3)
 210#define __PER_CPU_SEG                   (GDT_ENTRY_PER_CPU*8 + 3)
 211
 212#endif
 213
 214#ifndef CONFIG_PARAVIRT
 215# define get_kernel_rpl()               0
 216#endif
 217
 218#define IDT_ENTRIES                     256
 219#define NUM_EXCEPTION_VECTORS           32
 220
 221/* Bitmask of exception vectors which push an error code on the stack: */
 222#define EXCEPTION_ERRCODE_MASK          0x00027d00
 223
 224#define GDT_SIZE                        (GDT_ENTRIES*8)
 225#define GDT_ENTRY_TLS_ENTRIES           3
 226#define TLS_SIZE                        (GDT_ENTRY_TLS_ENTRIES* 8)
 227
 228#ifdef __KERNEL__
 229
 230/*
 231 * early_idt_handler_array is an array of entry points referenced in the
 232 * early IDT.  For simplicity, it's a real array with one entry point
 233 * every nine bytes.  That leaves room for an optional 'push $0' if the
 234 * vector has no error code (two bytes), a 'push $vector_number' (two
 235 * bytes), and a jump to the common entry code (up to five bytes).
 236 */
 237#define EARLY_IDT_HANDLER_SIZE 9
 238
 239/*
 240 * xen_early_idt_handler_array is for Xen pv guests: for each entry in
 241 * early_idt_handler_array it contains a prequel in the form of
 242 * pop %rcx; pop %r11; jmp early_idt_handler_array[i]; summing up to
 243 * max 8 bytes.
 244 */
 245#define XEN_EARLY_IDT_HANDLER_SIZE 8
 246
 247#ifndef __ASSEMBLY__
 248
 249extern const char early_idt_handler_array[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_SIZE];
 250extern void early_ignore_irq(void);
 251
 252#if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
 253extern const char xen_early_idt_handler_array[NUM_EXCEPTION_VECTORS][XEN_EARLY_IDT_HANDLER_SIZE];
 254#endif
 255
 256/*
 257 * Load a segment. Fall back on loading the zero segment if something goes
 258 * wrong.  This variant assumes that loading zero fully clears the segment.
 259 * This is always the case on Intel CPUs and, even on 64-bit AMD CPUs, any
 260 * failure to fully clear the cached descriptor is only observable for
 261 * FS and GS.
 262 */
 263#define __loadsegment_simple(seg, value)                                \
 264do {                                                                    \
 265        unsigned short __val = (value);                                 \
 266                                                                        \
 267        asm volatile("                                          \n"     \
 268                     "1:        movl %k0,%%" #seg "             \n"     \
 269                                                                        \
 270                     ".section .fixup,\"ax\"                    \n"     \
 271                     "2:        xorl %k0,%k0                    \n"     \
 272                     "          jmp 1b                          \n"     \
 273                     ".previous                                 \n"     \
 274                                                                        \
 275                     _ASM_EXTABLE(1b, 2b)                               \
 276                                                                        \
 277                     : "+r" (__val) : : "memory");                      \
 278} while (0)
 279
 280#define __loadsegment_ss(value) __loadsegment_simple(ss, (value))
 281#define __loadsegment_ds(value) __loadsegment_simple(ds, (value))
 282#define __loadsegment_es(value) __loadsegment_simple(es, (value))
 283
 284#ifdef CONFIG_X86_32
 285
 286/*
 287 * On 32-bit systems, the hidden parts of FS and GS are unobservable if
 288 * the selector is NULL, so there's no funny business here.
 289 */
 290#define __loadsegment_fs(value) __loadsegment_simple(fs, (value))
 291#define __loadsegment_gs(value) __loadsegment_simple(gs, (value))
 292
 293#else
 294
 295static inline void __loadsegment_fs(unsigned short value)
 296{
 297        asm volatile("                                          \n"
 298                     "1:        movw %0, %%fs                   \n"
 299                     "2:                                        \n"
 300
 301                     _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_clear_fs)
 302
 303                     : : "rm" (value) : "memory");
 304}
 305
 306/* __loadsegment_gs is intentionally undefined.  Use load_gs_index instead. */
 307
 308#endif
 309
 310#define loadsegment(seg, value) __loadsegment_ ## seg (value)
 311
 312/*
 313 * Save a segment register away:
 314 */
 315#define savesegment(seg, value)                         \
 316        asm("mov %%" #seg ",%0":"=r" (value) : : "memory")
 317
 318/*
 319 * x86-32 user GS accessors:
 320 */
 321#ifdef CONFIG_X86_32
 322# ifdef CONFIG_X86_32_LAZY_GS
 323#  define get_user_gs(regs)             (u16)({ unsigned long v; savesegment(gs, v); v; })
 324#  define set_user_gs(regs, v)          loadsegment(gs, (unsigned long)(v))
 325#  define task_user_gs(tsk)             ((tsk)->thread.gs)
 326#  define lazy_save_gs(v)               savesegment(gs, (v))
 327#  define lazy_load_gs(v)               loadsegment(gs, (v))
 328# else  /* X86_32_LAZY_GS */
 329#  define get_user_gs(regs)             (u16)((regs)->gs)
 330#  define set_user_gs(regs, v)          do { (regs)->gs = (v); } while (0)
 331#  define task_user_gs(tsk)             (task_pt_regs(tsk)->gs)
 332#  define lazy_save_gs(v)               do { } while (0)
 333#  define lazy_load_gs(v)               do { } while (0)
 334# endif /* X86_32_LAZY_GS */
 335#endif  /* X86_32 */
 336
 337#endif /* !__ASSEMBLY__ */
 338#endif /* __KERNEL__ */
 339
 340#endif /* _ASM_X86_SEGMENT_H */
 341