1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 2#ifndef _ASM_X86_UCONTEXT_H
 3#define _ASM_X86_UCONTEXT_H
 4
 5/*
 6 * Indicates the presence of extended state information in the memory
 7 * layout pointed by the fpstate pointer in the ucontext's sigcontext
 8 * struct (uc_mcontext).
 9 */
10#define UC_FP_XSTATE	0x1
11
12#ifdef __x86_64__
13/*
14 * UC_SIGCONTEXT_SS will be set when delivering 64-bit or x32 signals on
15 * kernels that save SS in the sigcontext.  All kernels that set
16 * UC_SIGCONTEXT_SS will correctly restore at least the low 32 bits of esp
17 * regardless of SS (i.e. they implement espfix).
18 *
19 * Kernels that set UC_SIGCONTEXT_SS will also set UC_STRICT_RESTORE_SS
20 * when delivering a signal that came from 64-bit code.
21 *
22 * Sigreturn restores SS as follows:
23 *
24 * if (saved SS is valid || UC_STRICT_RESTORE_SS is set ||
25 *     saved CS is not 64-bit)
26 *         new SS = saved SS  (will fail IRET and signal if invalid)
27 * else
28 *         new SS = a flat 32-bit data segment
29 *
30 * This behavior serves three purposes:
31 *
32 * - Legacy programs that construct a 64-bit sigcontext from scratch
33 *   with zero or garbage in the SS slot (e.g. old CRIU) and call
34 *   sigreturn will still work.
35 *
36 * - Old DOSEMU versions sometimes catch a signal from a segmented
37 *   context, delete the old SS segment (with modify_ldt), and change
38 *   the saved CS to a 64-bit segment.  These DOSEMU versions expect
39 *   sigreturn to send them back to 64-bit mode without killing them,
40 *   despite the fact that the SS selector when the signal was raised is
41 *   no longer valid.  UC_STRICT_RESTORE_SS will be clear, so the kernel
42 *   will fix up SS for these DOSEMU versions.
43 *
44 * - Old and new programs that catch a signal and return without
45 *   modifying the saved context will end up in exactly the state they
46 *   started in, even if they were running in a segmented context when
47 *   the signal was raised..  Old kernels would lose track of the
48 *   previous SS value.
49 */
50#define UC_SIGCONTEXT_SS	0x2
51#define UC_STRICT_RESTORE_SS	0x4
52#endif
53
54#include <asm-generic/ucontext.h>
55
56#endif /* _ASM_X86_UCONTEXT_H */

 1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 2#ifndef _ASM_X86_UCONTEXT_H
 3#define _ASM_X86_UCONTEXT_H
 4
 5/*
 6 * Indicates the presence of extended state information in the memory
 7 * layout pointed by the fpstate pointer in the ucontext's sigcontext
 8 * struct (uc_mcontext).
 9 */
10#define UC_FP_XSTATE	0x1
11
12#ifdef __x86_64__
13/*
14 * UC_SIGCONTEXT_SS will be set when delivering 64-bit or x32 signals on
15 * kernels that save SS in the sigcontext.  All kernels that set
16 * UC_SIGCONTEXT_SS will correctly restore at least the low 32 bits of esp
17 * regardless of SS (i.e. they implement espfix).
18 *
19 * Kernels that set UC_SIGCONTEXT_SS will also set UC_STRICT_RESTORE_SS
20 * when delivering a signal that came from 64-bit code.
21 *
22 * Sigreturn restores SS as follows:
23 *
24 * if (saved SS is valid || UC_STRICT_RESTORE_SS is set ||
25 *     saved CS is not 64-bit)
26 *         new SS = saved SS  (will fail IRET and signal if invalid)
27 * else
28 *         new SS = a flat 32-bit data segment
29 *
30 * This behavior serves three purposes:
31 *
32 * - Legacy programs that construct a 64-bit sigcontext from scratch
33 *   with zero or garbage in the SS slot (e.g. old CRIU) and call
34 *   sigreturn will still work.
35 *
36 * - Old DOSEMU versions sometimes catch a signal from a segmented
37 *   context, delete the old SS segment (with modify_ldt), and change
38 *   the saved CS to a 64-bit segment.  These DOSEMU versions expect
39 *   sigreturn to send them back to 64-bit mode without killing them,
40 *   despite the fact that the SS selector when the signal was raised is
41 *   no longer valid.  UC_STRICT_RESTORE_SS will be clear, so the kernel
42 *   will fix up SS for these DOSEMU versions.
43 *
44 * - Old and new programs that catch a signal and return without
45 *   modifying the saved context will end up in exactly the state they
46 *   started in, even if they were running in a segmented context when
47 *   the signal was raised..  Old kernels would lose track of the
48 *   previous SS value.
49 */
50#define UC_SIGCONTEXT_SS	0x2
51#define UC_STRICT_RESTORE_SS	0x4
52#endif
53
54#include <asm-generic/ucontext.h>
55
56#endif /* _ASM_X86_UCONTEXT_H */