1 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
2 /*
3 * ldt.h
4 *
5 * Definitions of structures used with the modify_ldt system call.
6 */
7 #ifndef _ASM_X86_LDT_H
8 #define _ASM_X86_LDT_H
9
10 /* Maximum number of LDT entries supported. */
11 #define LDT_ENTRIES 8192
12 /* The size of each LDT entry. */
13 #define LDT_ENTRY_SIZE 8
14
15 #ifndef __ASSEMBLY__
16 /*
17 * Note on 64bit base and limit is ignored and you cannot set DS/ES/CS
18 * not to the default values if you still want to do syscalls. This
19 * call is more for 32bit mode therefore.
20 */
21 struct user_desc {
22 unsigned int entry_number;
23 unsigned int base_addr;
24 unsigned int limit;
25 unsigned int seg_32bit:1;
26 unsigned int contents:2;
27 unsigned int read_exec_only:1;
28 unsigned int limit_in_pages:1;
29 unsigned int seg_not_present:1;
30 unsigned int useable:1;
31 #ifdef __x86_64__
32 /*
33 * Because this bit is not present in 32-bit user code, user
34 * programs can pass uninitialized values here. Therefore, in
35 * any context in which a user_desc comes from a 32-bit program,
36 * the kernel must act as though lm == 0, regardless of the
37 * actual value.
38 */
39 unsigned int lm:1;
40 #endif
41 };
42
43 #define MODIFY_LDT_CONTENTS_DATA 0
44 #define MODIFY_LDT_CONTENTS_STACK 1
45 #define MODIFY_LDT_CONTENTS_CODE 2
46
47 #endif /* !__ASSEMBLY__ */
48 #endif /* _ASM_X86_LDT_H */
49
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