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back to 64-bit mode without killing them, 40 * despite the fact that the SS selector when the signal was raised is 41 * no longer valid.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 */