entry-common.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2#ifndef _ASM_X86_ENTRY_COMMON_H
  3#define _ASM_X86_ENTRY_COMMON_H
  4
  5#include <linux/randomize_kstack.h>
  6#include <linux/user-return-notifier.h>
  7
  8#include <asm/nospec-branch.h>
  9#include <asm/io_bitmap.h>
 10#include <asm/fpu/api.h>
 11#include <asm/fred.h>
 12
 13/* Check that the stack and regs on entry from user mode are sane. */
 14static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
 15{
 16	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
 17		/*
 18		 * Make sure that the entry code gave us a sensible EFLAGS
 19		 * register.  Native because we want to check the actual CPU
 20		 * state, not the interrupt state as imagined by Xen.
 21		 */
 22		unsigned long flags = native_save_fl();
 23		unsigned long mask = X86_EFLAGS_DF | X86_EFLAGS_NT;
 24
 25		/*
 26		 * For !SMAP hardware we patch out CLAC on entry.
 27		 */
 28		if (cpu_feature_enabled(X86_FEATURE_SMAP) ||
 29		    cpu_feature_enabled(X86_FEATURE_XENPV))
 30			mask |= X86_EFLAGS_AC;
 31
 32		WARN_ON_ONCE(flags & mask);
 33
 34		/* We think we came from user mode. Make sure pt_regs agrees. */
 35		WARN_ON_ONCE(!user_mode(regs));
 36
 37		/*
 38		 * All entries from user mode (except #DF) should be on the
 39		 * normal thread stack and should have user pt_regs in the
 40		 * correct location.
 41		 */
 42		WARN_ON_ONCE(!on_thread_stack());
 43		WARN_ON_ONCE(regs != task_pt_regs(current));
 44	}
 45}
 46#define arch_enter_from_user_mode arch_enter_from_user_mode
 47
 48static inline void arch_exit_work(unsigned long ti_work)
 49{
 50	if (ti_work & _TIF_USER_RETURN_NOTIFY)
 51		fire_user_return_notifiers();
 52
 53	if (unlikely(ti_work & _TIF_IO_BITMAP))
 54		tss_update_io_bitmap();
 55
 56	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
 57		switch_fpu_return();
 58}
 59
 60static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 61						  unsigned long ti_work)
 62{
 63	fpregs_assert_state_consistent();
 64
 65	if (unlikely(ti_work))
 66		arch_exit_work(ti_work);
 67
 68	fred_update_rsp0();
 69
 70#ifdef CONFIG_COMPAT
 71	/*
 72	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 73	 * returning to user mode.  We need to clear it *after* signal
 74	 * handling, because syscall restart has a fixup for compat
 75	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
 76	 * selftest.
 77	 *
 78	 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 79	 * special case only applies after poking regs and before the
 80	 * very next return to user mode.
 81	 */
 82	current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED);
 83#endif
 84
 85	/*
 86	 * This value will get limited by KSTACK_OFFSET_MAX(), which is 10
 87	 * bits. The actual entropy will be further reduced by the compiler
 88	 * when applying stack alignment constraints (see cc_stack_align4/8 in
 89	 * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32)
 90	 * low bits from any entropy chosen here.
 91	 *
 92	 * Therefore, final stack offset entropy will be 7 (x86_64) or
 93	 * 8 (ia32) bits.
 94	 */
 95	choose_random_kstack_offset(rdtsc());
 96
 97	/* Avoid unnecessary reads of 'x86_ibpb_exit_to_user' */
 98	if (cpu_feature_enabled(X86_FEATURE_IBPB_EXIT_TO_USER) &&
 99	    this_cpu_read(x86_ibpb_exit_to_user)) {
100		indirect_branch_prediction_barrier();
101		this_cpu_write(x86_ibpb_exit_to_user, false);
102	}
103}
104#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
105
106static __always_inline void arch_exit_to_user_mode(void)
107{
108	amd_clear_divider();
109}
110#define arch_exit_to_user_mode arch_exit_to_user_mode
111
112#endif