1*4882a593Smuzhiyun /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ 2*4882a593Smuzhiyun #ifndef _ASM_X86_UCONTEXT_H 3*4882a593Smuzhiyun #define _ASM_X86_UCONTEXT_H 4*4882a593Smuzhiyun 5*4882a593Smuzhiyun /* 6*4882a593Smuzhiyun * Indicates the presence of extended state information in the memory 7*4882a593Smuzhiyun * layout pointed by the fpstate pointer in the ucontext's sigcontext 8*4882a593Smuzhiyun * struct (uc_mcontext). 9*4882a593Smuzhiyun */ 10*4882a593Smuzhiyun #define UC_FP_XSTATE 0x1 11*4882a593Smuzhiyun 12*4882a593Smuzhiyun #ifdef __x86_64__ 13*4882a593Smuzhiyun /* 14*4882a593Smuzhiyun * UC_SIGCONTEXT_SS will be set when delivering 64-bit or x32 signals on 15*4882a593Smuzhiyun * kernels that save SS in the sigcontext. All kernels that set 16*4882a593Smuzhiyun * UC_SIGCONTEXT_SS will correctly restore at least the low 32 bits of esp 17*4882a593Smuzhiyun * regardless of SS (i.e. they implement espfix). 18*4882a593Smuzhiyun * 19*4882a593Smuzhiyun * Kernels that set UC_SIGCONTEXT_SS will also set UC_STRICT_RESTORE_SS 20*4882a593Smuzhiyun * when delivering a signal that came from 64-bit code. 21*4882a593Smuzhiyun * 22*4882a593Smuzhiyun * Sigreturn restores SS as follows: 23*4882a593Smuzhiyun * 24*4882a593Smuzhiyun * if (saved SS is valid || UC_STRICT_RESTORE_SS is set || 25*4882a593Smuzhiyun * saved CS is not 64-bit) 26*4882a593Smuzhiyun * new SS = saved SS (will fail IRET and signal if invalid) 27*4882a593Smuzhiyun * else 28*4882a593Smuzhiyun * new SS = a flat 32-bit data segment 29*4882a593Smuzhiyun * 30*4882a593Smuzhiyun * This behavior serves three purposes: 31*4882a593Smuzhiyun * 32*4882a593Smuzhiyun * - Legacy programs that construct a 64-bit sigcontext from scratch 33*4882a593Smuzhiyun * with zero or garbage in the SS slot (e.g. old CRIU) and call 34*4882a593Smuzhiyun * sigreturn will still work. 35*4882a593Smuzhiyun * 36*4882a593Smuzhiyun * - Old DOSEMU versions sometimes catch a signal from a segmented 37*4882a593Smuzhiyun * context, delete the old SS segment (with modify_ldt), and change 38*4882a593Smuzhiyun * the saved CS to a 64-bit segment. These DOSEMU versions expect 39*4882a593Smuzhiyun * sigreturn to send them back to 64-bit mode without killing them, 40*4882a593Smuzhiyun * despite the fact that the SS selector when the signal was raised is 41*4882a593Smuzhiyun * no longer valid. UC_STRICT_RESTORE_SS will be clear, so the kernel 42*4882a593Smuzhiyun * will fix up SS for these DOSEMU versions. 43*4882a593Smuzhiyun * 44*4882a593Smuzhiyun * - Old and new programs that catch a signal and return without 45*4882a593Smuzhiyun * modifying the saved context will end up in exactly the state they 46*4882a593Smuzhiyun * started in, even if they were running in a segmented context when 47*4882a593Smuzhiyun * the signal was raised.. Old kernels would lose track of the 48*4882a593Smuzhiyun * previous SS value. 49*4882a593Smuzhiyun */ 50*4882a593Smuzhiyun #define UC_SIGCONTEXT_SS 0x2 51*4882a593Smuzhiyun #define UC_STRICT_RESTORE_SS 0x4 52*4882a593Smuzhiyun #endif 53*4882a593Smuzhiyun 54*4882a593Smuzhiyun #include <asm-generic/ucontext.h> 55*4882a593Smuzhiyun 56*4882a593Smuzhiyun #endif /* _ASM_X86_UCONTEXT_H */ 57