Christopher Ferris | 2598113 | 2017-11-14 16:53:49 -0800 | [diff] [blame] | 1 | /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ |
Christopher Ferris | 0437c52 | 2013-11-07 14:16:29 -0800 | [diff] [blame] | 2 | #ifndef _ASM_X86_UCONTEXT_H |
| 3 | #define _ASM_X86_UCONTEXT_H |
| 4 | |
Christopher Ferris | ccfaccd | 2016-08-24 12:11:31 -0700 | [diff] [blame] | 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| 41 | * no longer valid.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 |
Christopher Ferris | 0437c52 | 2013-11-07 14:16:29 -0800 | [diff] [blame] | 53 | |
| 54 | #include <asm-generic/ucontext.h> |
| 55 | |
| 56 | #endif /* _ASM_X86_UCONTEXT_H */ |