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41 | * no longer valid.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 | |