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41  *   no longer valid.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 */
57