LXR linux/arch/x86/include/uapi/asm/ucontext.h

   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  41 *   no longer valid.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