#ifndef _ASM_X86_UCONTEXT_H
#define _ASM_X86_UCONTEXT_H
-#define UC_FP_XSTATE 0x1 /* indicates the presence of extended state
- * information in the memory layout pointed
- * by the fpstate pointer in the ucontext's
- * sigcontext struct (uc_mcontext).
- */
+/*
+ * Indicates the presence of extended state information in the memory
+ * layout pointed by the fpstate pointer in the ucontext's sigcontext
+ * struct (uc_mcontext).
+ */
+#define UC_FP_XSTATE 0x1
+
+#ifdef __x86_64__
+/*
+ * UC_SIGCONTEXT_SS will be set when delivering 64-bit or x32 signals on
+ * kernels that save SS in the sigcontext. All kernels that set
+ * UC_SIGCONTEXT_SS will correctly restore at least the low 32 bits of esp
+ * regardless of SS (i.e. they implement espfix).
+ *
+ * Kernels that set UC_SIGCONTEXT_SS will also set UC_STRICT_RESTORE_SS
+ * when delivering a signal that came from 64-bit code.
+ *
+ * Sigreturn restores SS as follows:
+ *
+ * if (saved SS is valid || UC_STRICT_RESTORE_SS is set ||
+ * saved CS is not 64-bit)
+ * new SS = saved SS (will fail IRET and signal if invalid)
+ * else
+ * new SS = a flat 32-bit data segment
+ *
+ * This behavior serves three purposes:
+ *
+ * - Legacy programs that construct a 64-bit sigcontext from scratch
+ * with zero or garbage in the SS slot (e.g. old CRIU) and call
+ * sigreturn will still work.
+ *
+ * - Old DOSEMU versions sometimes catch a signal from a segmented
+ * context, delete the old SS segment (with modify_ldt), and change
+ * the saved CS to a 64-bit segment. These DOSEMU versions expect
+ * sigreturn to send them back to 64-bit mode without killing them,
+ * despite the fact that the SS selector when the signal was raised is
+ * no longer valid. UC_STRICT_RESTORE_SS will be clear, so the kernel
+ * will fix up SS for these DOSEMU versions.
+ *
+ * - Old and new programs that catch a signal and return without
+ * modifying the saved context will end up in exactly the state they
+ * started in, even if they were running in a segmented context when
+ * the signal was raised.. Old kernels would lose track of the
+ * previous SS value.
+ */
+#define UC_SIGCONTEXT_SS 0x2
+#define UC_STRICT_RESTORE_SS 0x4
+#endif
#include <asm-generic/ucontext.h>
}
#endif
-int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
+static int restore_sigcontext(struct pt_regs *regs,
+ struct sigcontext __user *sc,
+ unsigned long uc_flags)
{
unsigned long buf_val;
void __user *buf;
COPY(r15);
#endif /* CONFIG_X86_64 */
-#ifdef CONFIG_X86_32
COPY_SEG_CPL3(cs);
COPY_SEG_CPL3(ss);
-#else /* !CONFIG_X86_32 */
- /* Kernel saves and restores only the CS segment register on signals,
- * which is the bare minimum needed to allow mixed 32/64-bit code.
- * App's signal handler can save/restore other segments if needed. */
- COPY_SEG_CPL3(cs);
-#endif /* CONFIG_X86_32 */
+
+#ifdef CONFIG_X86_64
+ /*
+ * Fix up SS if needed for the benefit of old DOSEMU and
+ * CRIU.
+ */
+ if (unlikely(!(uc_flags & UC_STRICT_RESTORE_SS) &&
+ user_64bit_mode(regs)))
+ force_valid_ss(regs);
+#endif
get_user_ex(tmpflags, &sc->flags);
regs->flags = (regs->flags & ~FIX_EFLAGS) | (tmpflags & FIX_EFLAGS);
put_user_ex(regs->cs, &sc->cs);
put_user_ex(0, &sc->gs);
put_user_ex(0, &sc->fs);
+ put_user_ex(regs->ss, &sc->ss);
#endif /* CONFIG_X86_32 */
put_user_ex(fpstate, &sc->fpstate);
return 0;
}
#else /* !CONFIG_X86_32 */
+static unsigned long frame_uc_flags(struct pt_regs *regs)
+{
+ unsigned long flags;
+
+ if (cpu_has_xsave)
+ flags = UC_FP_XSTATE | UC_SIGCONTEXT_SS;
+ else
+ flags = UC_SIGCONTEXT_SS;
+
+ if (likely(user_64bit_mode(regs)))
+ flags |= UC_STRICT_RESTORE_SS;
+
+ return flags;
+}
+
static int __setup_rt_frame(int sig, struct ksignal *ksig,
sigset_t *set, struct pt_regs *regs)
{
put_user_try {
/* Create the ucontext. */
- if (cpu_has_xsave)
- put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
- else
- put_user_ex(0, &frame->uc.uc_flags);
+ put_user_ex(frame_uc_flags(regs), &frame->uc.uc_flags);
put_user_ex(0, &frame->uc.uc_link);
save_altstack_ex(&frame->uc.uc_stack, regs->sp);
put_user_try {
/* Create the ucontext. */
- if (cpu_has_xsave)
- put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
- else
- put_user_ex(0, &frame->uc.uc_flags);
+ put_user_ex(frame_uc_flags(regs), &frame->uc.uc_flags);
put_user_ex(0, &frame->uc.uc_link);
compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);
put_user_ex(0, &frame->uc.uc__pad0);
set_current_blocked(&set);
- if (restore_sigcontext(regs, &frame->sc))
+ /*
+ * x86_32 has no uc_flags bits relevant to restore_sigcontext.
+ * Save a few cycles by skipping the __get_user.
+ */
+ if (restore_sigcontext(regs, &frame->sc, 0))
goto badframe;
return regs->ax;
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe __user *frame;
sigset_t set;
+ unsigned long uc_flags;
frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
goto badframe;
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;
+ if (__get_user(uc_flags, &frame->uc.uc_flags))
+ goto badframe;
set_current_blocked(&set);
- if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
+ if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (restore_altstack(&frame->uc.uc_stack))
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe_x32 __user *frame;
sigset_t set;
+ unsigned long uc_flags;
frame = (struct rt_sigframe_x32 __user *)(regs->sp - 8);
goto badframe;
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;
+ if (__get_user(uc_flags, &frame->uc.uc_flags))
+ goto badframe;
set_current_blocked(&set);
- if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
+ if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (compat_restore_altstack(&frame->uc.uc_stack))
projects / users / hch / configfs.git / commitdiff