1 /* SPDX-License-Identifier: GPL-2.0 */
3 * Compatibility mode system call entry point for x86-64.
5 * Copyright 2000-2002 Andi Kleen, SuSE Labs.
7 #include <asm/asm-offsets.h>
8 #include <asm/current.h>
10 #include <asm/thread_info.h>
11 #include <asm/segment.h>
12 #include <asm/irqflags.h>
15 #include <asm/nospec-branch.h>
16 #include <linux/linkage.h>
17 #include <linux/err.h>
21 .section .entry.text, "ax"
24 * 32-bit SYSENTER entry.
26 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
27 * on 64-bit kernels running on Intel CPUs.
29 * The SYSENTER instruction, in principle, should *only* occur in the
30 * vDSO. In practice, a small number of Android devices were shipped
31 * with a copy of Bionic that inlined a SYSENTER instruction. This
32 * never happened in any of Google's Bionic versions -- it only happened
33 * in a narrow range of Intel-provided versions.
35 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
36 * IF and VM in RFLAGS are cleared (IOW: interrupts are off).
37 * SYSENTER does not save anything on the stack,
38 * and does not save old RIP (!!!), RSP, or RFLAGS.
41 * eax system call number
50 SYM_CODE_START(entry_SYSENTER_compat)
53 /* Interrupts are off on entry. */
57 SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
60 movq PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp
62 /* Construct struct pt_regs on stack */
63 pushq $__USER_DS /* pt_regs->ss */
64 pushq $0 /* pt_regs->sp = 0 (placeholder) */
67 * Push flags. This is nasty. First, interrupts are currently
68 * off, but we need pt_regs->flags to have IF set. Second, if TS
69 * was set in usermode, it's still set, and we're singlestepping
70 * through this code. do_SYSENTER_32() will fix up IF.
72 pushfq /* pt_regs->flags (except IF = 0) */
73 pushq $__USER32_CS /* pt_regs->cs */
74 pushq $0 /* pt_regs->ip = 0 (placeholder) */
75 SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
78 * User tracing code (ptrace or signal handlers) might assume that
79 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
80 * syscall. Just in case the high bits are nonzero, zero-extend
81 * the syscall number. (This could almost certainly be deleted
82 * with no ill effects.)
86 pushq %rax /* pt_regs->orig_ax */
87 PUSH_AND_CLEAR_REGS rax=$-ENOSYS
97 * SYSENTER doesn't filter flags, so we need to clear NT and AC
98 * ourselves. To save a few cycles, we can check whether
99 * either was set instead of doing an unconditional popfq.
100 * This needs to happen before enabling interrupts so that
101 * we don't get preempted with NT set.
103 * If TF is set, we will single-step all the way to here -- do_debug
104 * will ignore all the traps. (Yes, this is slow, but so is
105 * single-stepping in general. This allows us to avoid having
106 * a more complicated code to handle the case where a user program
107 * forces us to single-step through the SYSENTER entry code.)
109 * NB.: .Lsysenter_fix_flags is a label with the code under it moved
110 * out-of-line as an optimization: NT is unlikely to be set in the
111 * majority of the cases and instead of polluting the I$ unnecessarily,
112 * we're keeping that code behind a branch which will predict as
113 * not-taken and therefore its instructions won't be fetched.
115 testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
116 jnz .Lsysenter_fix_flags
117 .Lsysenter_flags_fixed:
121 jmp sysret32_from_system_call
123 .Lsysenter_fix_flags:
124 pushq $X86_EFLAGS_FIXED
126 jmp .Lsysenter_flags_fixed
127 SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
128 SYM_CODE_END(entry_SYSENTER_compat)
131 * 32-bit SYSCALL entry.
133 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
134 * on 64-bit kernels running on AMD CPUs.
136 * The SYSCALL instruction, in principle, should *only* occur in the
137 * vDSO. In practice, it appears that this really is the case.
140 * - The calling convention for SYSCALL has changed several times without
143 * - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
144 * user task that did SYSCALL without immediately reloading SS
145 * would randomly crash.
147 * - Most programmers do not directly target AMD CPUs, and the 32-bit
148 * SYSCALL instruction does not exist on Intel CPUs. Even on AMD
149 * CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
150 * because the SYSCALL instruction in legacy/native 32-bit mode (as
151 * opposed to compat mode) is sufficiently poorly designed as to be
152 * essentially unusable.
154 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
155 * RFLAGS to R11, then loads new SS, CS, and RIP from previously
156 * programmed MSRs. RFLAGS gets masked by a value from another MSR
157 * (so CLD and CLAC are not needed). SYSCALL does not save anything on
158 * the stack and does not change RSP.
160 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode
161 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
162 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
163 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
164 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
167 * eax system call number
170 * ebp arg2 (note: not saved in the stack frame, should not be touched)
177 SYM_CODE_START(entry_SYSCALL_compat)
180 /* Interrupts are off on entry. */
186 /* Use %rsp as scratch reg. User ESP is stashed in r8 */
187 SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
189 /* Switch to the kernel stack */
190 movq PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp
192 SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
195 /* Construct struct pt_regs on stack */
196 pushq $__USER_DS /* pt_regs->ss */
197 pushq %r8 /* pt_regs->sp */
198 pushq %r11 /* pt_regs->flags */
199 pushq $__USER32_CS /* pt_regs->cs */
200 pushq %rcx /* pt_regs->ip */
201 SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
202 movl %eax, %eax /* discard orig_ax high bits */
203 pushq %rax /* pt_regs->orig_ax */
204 PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS
212 call do_fast_syscall_32
214 sysret32_from_system_call:
215 /* XEN PV guests always use IRET path */
216 ALTERNATIVE "testb %al, %al; jz swapgs_restore_regs_and_return_to_usermode", \
217 "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
220 * Opportunistic SYSRET
222 * We are not going to return to userspace from the trampoline
223 * stack. So let's erase the thread stack right now.
229 movq RBX(%rsp), %rbx /* pt_regs->rbx */
230 movq RBP(%rsp), %rbp /* pt_regs->rbp */
231 movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
232 movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */
233 addq $RAX, %rsp /* Skip r8-r15 */
234 popq %rax /* pt_regs->rax */
235 popq %rdx /* Skip pt_regs->cx */
236 popq %rdx /* pt_regs->dx */
237 popq %rsi /* pt_regs->si */
238 popq %rdi /* pt_regs->di */
241 * USERGS_SYSRET32 does:
242 * GSBASE = user's GS base
248 * ECX will not match pt_regs->cx, but we're returning to a vDSO
249 * trampoline that will fix up RCX, so this is okay.
251 * R12-R15 are callee-saved, so they contain whatever was in them
252 * when the system call started, which is already known to user
253 * code. We zero R8-R10 to avoid info leaks.
255 movq RSP-ORIG_RAX(%rsp), %rsp
256 SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
260 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
261 * on the process stack which is not mapped to userspace and
262 * not readable after we SWITCH_TO_USER_CR3. Delay the CR3
263 * switch until after after the last reference to the process
266 * %r8/%r9 are zeroed before the sysret, thus safe to clobber.
268 SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9
276 SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
279 SYM_CODE_END(entry_SYSCALL_compat)
282 * int 0x80 is used by 32 bit mode as a system call entry. Normally idt entries
283 * point to C routines, however since this is a system call interface the branch
284 * history needs to be scrubbed to protect against BHI attacks, and that
285 * scrubbing needs to take place in assembly code prior to entering any C
288 SYM_CODE_START(int80_emulation)
292 jmp do_int80_emulation
293 SYM_CODE_END(int80_emulation)