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 
12 /* Check that the stack and regs on entry from user mode are sane. */
arch_enter_from_user_mode(struct pt_regs * regs)13 static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
14 {
15 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
16 		/*
17 		 * Make sure that the entry code gave us a sensible EFLAGS
18 		 * register.  Native because we want to check the actual CPU
19 		 * state, not the interrupt state as imagined by Xen.
20 		 */
21 		unsigned long flags = native_save_fl();
22 		unsigned long mask = X86_EFLAGS_DF | X86_EFLAGS_NT;
23 
24 		/*
25 		 * For !SMAP hardware we patch out CLAC on entry.
26 		 */
27 		if (cpu_feature_enabled(X86_FEATURE_SMAP) ||
28 		    cpu_feature_enabled(X86_FEATURE_XENPV))
29 			mask |= X86_EFLAGS_AC;
30 
31 		WARN_ON_ONCE(flags & mask);
32 
33 		/* We think we came from user mode. Make sure pt_regs agrees. */
34 		WARN_ON_ONCE(!user_mode(regs));
35 
36 		/*
37 		 * All entries from user mode (except #DF) should be on the
38 		 * normal thread stack and should have user pt_regs in the
39 		 * correct location.
40 		 */
41 		WARN_ON_ONCE(!on_thread_stack());
42 		WARN_ON_ONCE(regs != task_pt_regs(current));
43 	}
44 }
45 #define arch_enter_from_user_mode arch_enter_from_user_mode
46 
arch_exit_to_user_mode_prepare(struct pt_regs * regs,unsigned long ti_work)47 static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
48 						  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 	fpregs_assert_state_consistent();
57 	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
58 		switch_fpu_return();
59 
60 #ifdef CONFIG_COMPAT
61 	/*
62 	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
63 	 * returning to user mode.  We need to clear it *after* signal
64 	 * handling, because syscall restart has a fixup for compat
65 	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
66 	 * selftest.
67 	 *
68 	 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
69 	 * special case only applies after poking regs and before the
70 	 * very next return to user mode.
71 	 */
72 	current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED);
73 #endif
74 
75 	/*
76 	 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
77 	 * but not enough for x86 stack utilization comfort. To keep
78 	 * reasonable stack head room, reduce the maximum offset to 8 bits.
79 	 *
80 	 * The actual entropy will be further reduced by the compiler when
81 	 * applying stack alignment constraints (see cc_stack_align4/8 in
82 	 * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32)
83 	 * low bits from any entropy chosen here.
84 	 *
85 	 * Therefore, final stack offset entropy will be 5 (x86_64) or
86 	 * 6 (ia32) bits.
87 	 */
88 	choose_random_kstack_offset(rdtsc() & 0xFF);
89 }
90 #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
91 
arch_exit_to_user_mode(void)92 static __always_inline void arch_exit_to_user_mode(void)
93 {
94 	mds_user_clear_cpu_buffers();
95 }
96 #define arch_exit_to_user_mode arch_exit_to_user_mode
97 
98 #endif
99