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  41  *   no longer valid.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 */