xref: /openbmc/linux/arch/x86/entry/entry_64_compat.S (revision f5ad1c74)
1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Compatibility mode system call entry point for x86-64.
4 *
5 * Copyright 2000-2002 Andi Kleen, SuSE Labs.
6 */
7#include "calling.h"
8#include <asm/asm-offsets.h>
9#include <asm/current.h>
10#include <asm/errno.h>
11#include <asm/ia32_unistd.h>
12#include <asm/thread_info.h>
13#include <asm/segment.h>
14#include <asm/irqflags.h>
15#include <asm/asm.h>
16#include <asm/smap.h>
17#include <linux/linkage.h>
18#include <linux/err.h>
19
20	.section .entry.text, "ax"
21
22/*
23 * 32-bit SYSENTER entry.
24 *
25 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
26 * on 64-bit kernels running on Intel CPUs.
27 *
28 * The SYSENTER instruction, in principle, should *only* occur in the
29 * vDSO.  In practice, a small number of Android devices were shipped
30 * with a copy of Bionic that inlined a SYSENTER instruction.  This
31 * never happened in any of Google's Bionic versions -- it only happened
32 * in a narrow range of Intel-provided versions.
33 *
34 * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
35 * IF and VM in RFLAGS are cleared (IOW: interrupts are off).
36 * SYSENTER does not save anything on the stack,
37 * and does not save old RIP (!!!), RSP, or RFLAGS.
38 *
39 * Arguments:
40 * eax  system call number
41 * ebx  arg1
42 * ecx  arg2
43 * edx  arg3
44 * esi  arg4
45 * edi  arg5
46 * ebp  user stack
47 * 0(%ebp) arg6
48 */
49SYM_CODE_START(entry_SYSENTER_compat)
50	UNWIND_HINT_EMPTY
51	/* Interrupts are off on entry. */
52	SWAPGS
53
54	pushq	%rax
55	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
56	popq	%rax
57
58	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
59
60	/* Construct struct pt_regs on stack */
61	pushq	$__USER32_DS		/* pt_regs->ss */
62	pushq	$0			/* pt_regs->sp = 0 (placeholder) */
63
64	/*
65	 * Push flags.  This is nasty.  First, interrupts are currently
66	 * off, but we need pt_regs->flags to have IF set.  Second, if TS
67	 * was set in usermode, it's still set, and we're singlestepping
68	 * through this code.  do_SYSENTER_32() will fix up IF.
69	 */
70	pushfq				/* pt_regs->flags (except IF = 0) */
71	pushq	$__USER32_CS		/* pt_regs->cs */
72	pushq	$0			/* pt_regs->ip = 0 (placeholder) */
73SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
74
75	/*
76	 * User tracing code (ptrace or signal handlers) might assume that
77	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
78	 * syscall.  Just in case the high bits are nonzero, zero-extend
79	 * the syscall number.  (This could almost certainly be deleted
80	 * with no ill effects.)
81	 */
82	movl	%eax, %eax
83
84	pushq	%rax			/* pt_regs->orig_ax */
85	pushq	%rdi			/* pt_regs->di */
86	pushq	%rsi			/* pt_regs->si */
87	pushq	%rdx			/* pt_regs->dx */
88	pushq	%rcx			/* pt_regs->cx */
89	pushq	$-ENOSYS		/* pt_regs->ax */
90	pushq   $0			/* pt_regs->r8  = 0 */
91	xorl	%r8d, %r8d		/* nospec   r8 */
92	pushq   $0			/* pt_regs->r9  = 0 */
93	xorl	%r9d, %r9d		/* nospec   r9 */
94	pushq   $0			/* pt_regs->r10 = 0 */
95	xorl	%r10d, %r10d		/* nospec   r10 */
96	pushq   $0			/* pt_regs->r11 = 0 */
97	xorl	%r11d, %r11d		/* nospec   r11 */
98	pushq   %rbx                    /* pt_regs->rbx */
99	xorl	%ebx, %ebx		/* nospec   rbx */
100	pushq   %rbp                    /* pt_regs->rbp (will be overwritten) */
101	xorl	%ebp, %ebp		/* nospec   rbp */
102	pushq   $0			/* pt_regs->r12 = 0 */
103	xorl	%r12d, %r12d		/* nospec   r12 */
104	pushq   $0			/* pt_regs->r13 = 0 */
105	xorl	%r13d, %r13d		/* nospec   r13 */
106	pushq   $0			/* pt_regs->r14 = 0 */
107	xorl	%r14d, %r14d		/* nospec   r14 */
108	pushq   $0			/* pt_regs->r15 = 0 */
109	xorl	%r15d, %r15d		/* nospec   r15 */
110
111	UNWIND_HINT_REGS
112
113	cld
114
115	/*
116	 * SYSENTER doesn't filter flags, so we need to clear NT and AC
117	 * ourselves.  To save a few cycles, we can check whether
118	 * either was set instead of doing an unconditional popfq.
119	 * This needs to happen before enabling interrupts so that
120	 * we don't get preempted with NT set.
121	 *
122	 * If TF is set, we will single-step all the way to here -- do_debug
123	 * will ignore all the traps.  (Yes, this is slow, but so is
124	 * single-stepping in general.  This allows us to avoid having
125	 * a more complicated code to handle the case where a user program
126	 * forces us to single-step through the SYSENTER entry code.)
127	 *
128	 * NB.: .Lsysenter_fix_flags is a label with the code under it moved
129	 * out-of-line as an optimization: NT is unlikely to be set in the
130	 * majority of the cases and instead of polluting the I$ unnecessarily,
131	 * we're keeping that code behind a branch which will predict as
132	 * not-taken and therefore its instructions won't be fetched.
133	 */
134	testl	$X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
135	jnz	.Lsysenter_fix_flags
136.Lsysenter_flags_fixed:
137
138	movq	%rsp, %rdi
139	call	do_SYSENTER_32
140	/* XEN PV guests always use IRET path */
141	ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
142		    "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
143	jmp	sysret32_from_system_call
144
145.Lsysenter_fix_flags:
146	pushq	$X86_EFLAGS_FIXED
147	popfq
148	jmp	.Lsysenter_flags_fixed
149SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
150SYM_CODE_END(entry_SYSENTER_compat)
151
152/*
153 * 32-bit SYSCALL entry.
154 *
155 * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
156 * on 64-bit kernels running on AMD CPUs.
157 *
158 * The SYSCALL instruction, in principle, should *only* occur in the
159 * vDSO.  In practice, it appears that this really is the case.
160 * As evidence:
161 *
162 *  - The calling convention for SYSCALL has changed several times without
163 *    anyone noticing.
164 *
165 *  - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
166 *    user task that did SYSCALL without immediately reloading SS
167 *    would randomly crash.
168 *
169 *  - Most programmers do not directly target AMD CPUs, and the 32-bit
170 *    SYSCALL instruction does not exist on Intel CPUs.  Even on AMD
171 *    CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
172 *    because the SYSCALL instruction in legacy/native 32-bit mode (as
173 *    opposed to compat mode) is sufficiently poorly designed as to be
174 *    essentially unusable.
175 *
176 * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
177 * RFLAGS to R11, then loads new SS, CS, and RIP from previously
178 * programmed MSRs.  RFLAGS gets masked by a value from another MSR
179 * (so CLD and CLAC are not needed).  SYSCALL does not save anything on
180 * the stack and does not change RSP.
181 *
182 * Note: RFLAGS saving+masking-with-MSR happens only in Long mode
183 * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
184 * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
185 * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
186 * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
187 *
188 * Arguments:
189 * eax  system call number
190 * ecx  return address
191 * ebx  arg1
192 * ebp  arg2	(note: not saved in the stack frame, should not be touched)
193 * edx  arg3
194 * esi  arg4
195 * edi  arg5
196 * esp  user stack
197 * 0(%esp) arg6
198 */
199SYM_CODE_START(entry_SYSCALL_compat)
200	UNWIND_HINT_EMPTY
201	/* Interrupts are off on entry. */
202	swapgs
203
204	/* Stash user ESP */
205	movl	%esp, %r8d
206
207	/* Use %rsp as scratch reg. User ESP is stashed in r8 */
208	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
209
210	/* Switch to the kernel stack */
211	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
212
213	/* Construct struct pt_regs on stack */
214	pushq	$__USER32_DS		/* pt_regs->ss */
215	pushq	%r8			/* pt_regs->sp */
216	pushq	%r11			/* pt_regs->flags */
217	pushq	$__USER32_CS		/* pt_regs->cs */
218	pushq	%rcx			/* pt_regs->ip */
219SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
220	movl	%eax, %eax		/* discard orig_ax high bits */
221	pushq	%rax			/* pt_regs->orig_ax */
222	pushq	%rdi			/* pt_regs->di */
223	pushq	%rsi			/* pt_regs->si */
224	xorl	%esi, %esi		/* nospec   si */
225	pushq	%rdx			/* pt_regs->dx */
226	xorl	%edx, %edx		/* nospec   dx */
227	pushq	%rbp			/* pt_regs->cx (stashed in bp) */
228	xorl	%ecx, %ecx		/* nospec   cx */
229	pushq	$-ENOSYS		/* pt_regs->ax */
230	pushq   $0			/* pt_regs->r8  = 0 */
231	xorl	%r8d, %r8d		/* nospec   r8 */
232	pushq   $0			/* pt_regs->r9  = 0 */
233	xorl	%r9d, %r9d		/* nospec   r9 */
234	pushq   $0			/* pt_regs->r10 = 0 */
235	xorl	%r10d, %r10d		/* nospec   r10 */
236	pushq   $0			/* pt_regs->r11 = 0 */
237	xorl	%r11d, %r11d		/* nospec   r11 */
238	pushq   %rbx                    /* pt_regs->rbx */
239	xorl	%ebx, %ebx		/* nospec   rbx */
240	pushq   %rbp                    /* pt_regs->rbp (will be overwritten) */
241	xorl	%ebp, %ebp		/* nospec   rbp */
242	pushq   $0			/* pt_regs->r12 = 0 */
243	xorl	%r12d, %r12d		/* nospec   r12 */
244	pushq   $0			/* pt_regs->r13 = 0 */
245	xorl	%r13d, %r13d		/* nospec   r13 */
246	pushq   $0			/* pt_regs->r14 = 0 */
247	xorl	%r14d, %r14d		/* nospec   r14 */
248	pushq   $0			/* pt_regs->r15 = 0 */
249	xorl	%r15d, %r15d		/* nospec   r15 */
250
251	UNWIND_HINT_REGS
252
253	movq	%rsp, %rdi
254	call	do_fast_syscall_32
255	/* XEN PV guests always use IRET path */
256	ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
257		    "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
258
259	/* Opportunistic SYSRET */
260sysret32_from_system_call:
261	/*
262	 * We are not going to return to userspace from the trampoline
263	 * stack. So let's erase the thread stack right now.
264	 */
265	STACKLEAK_ERASE
266
267	movq	RBX(%rsp), %rbx		/* pt_regs->rbx */
268	movq	RBP(%rsp), %rbp		/* pt_regs->rbp */
269	movq	EFLAGS(%rsp), %r11	/* pt_regs->flags (in r11) */
270	movq	RIP(%rsp), %rcx		/* pt_regs->ip (in rcx) */
271	addq	$RAX, %rsp		/* Skip r8-r15 */
272	popq	%rax			/* pt_regs->rax */
273	popq	%rdx			/* Skip pt_regs->cx */
274	popq	%rdx			/* pt_regs->dx */
275	popq	%rsi			/* pt_regs->si */
276	popq	%rdi			/* pt_regs->di */
277
278        /*
279         * USERGS_SYSRET32 does:
280         *  GSBASE = user's GS base
281         *  EIP = ECX
282         *  RFLAGS = R11
283         *  CS = __USER32_CS
284         *  SS = __USER_DS
285         *
286	 * ECX will not match pt_regs->cx, but we're returning to a vDSO
287	 * trampoline that will fix up RCX, so this is okay.
288	 *
289	 * R12-R15 are callee-saved, so they contain whatever was in them
290	 * when the system call started, which is already known to user
291	 * code.  We zero R8-R10 to avoid info leaks.
292         */
293	movq	RSP-ORIG_RAX(%rsp), %rsp
294
295	/*
296	 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
297	 * on the process stack which is not mapped to userspace and
298	 * not readable after we SWITCH_TO_USER_CR3.  Delay the CR3
299	 * switch until after after the last reference to the process
300	 * stack.
301	 *
302	 * %r8/%r9 are zeroed before the sysret, thus safe to clobber.
303	 */
304	SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9
305
306	xorl	%r8d, %r8d
307	xorl	%r9d, %r9d
308	xorl	%r10d, %r10d
309	swapgs
310	sysretl
311SYM_CODE_END(entry_SYSCALL_compat)
312
313/*
314 * 32-bit legacy system call entry.
315 *
316 * 32-bit x86 Linux system calls traditionally used the INT $0x80
317 * instruction.  INT $0x80 lands here.
318 *
319 * This entry point can be used by 32-bit and 64-bit programs to perform
320 * 32-bit system calls.  Instances of INT $0x80 can be found inline in
321 * various programs and libraries.  It is also used by the vDSO's
322 * __kernel_vsyscall fallback for hardware that doesn't support a faster
323 * entry method.  Restarted 32-bit system calls also fall back to INT
324 * $0x80 regardless of what instruction was originally used to do the
325 * system call.
326 *
327 * This is considered a slow path.  It is not used by most libc
328 * implementations on modern hardware except during process startup.
329 *
330 * Arguments:
331 * eax  system call number
332 * ebx  arg1
333 * ecx  arg2
334 * edx  arg3
335 * esi  arg4
336 * edi  arg5
337 * ebp  arg6
338 */
339SYM_CODE_START(entry_INT80_compat)
340	UNWIND_HINT_EMPTY
341	/*
342	 * Interrupts are off on entry.
343	 */
344	ASM_CLAC			/* Do this early to minimize exposure */
345	SWAPGS
346
347	/*
348	 * User tracing code (ptrace or signal handlers) might assume that
349	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
350	 * syscall.  Just in case the high bits are nonzero, zero-extend
351	 * the syscall number.  (This could almost certainly be deleted
352	 * with no ill effects.)
353	 */
354	movl	%eax, %eax
355
356	/* switch to thread stack expects orig_ax and rdi to be pushed */
357	pushq	%rax			/* pt_regs->orig_ax */
358	pushq	%rdi			/* pt_regs->di */
359
360	/* Need to switch before accessing the thread stack. */
361	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
362
363	/* In the Xen PV case we already run on the thread stack. */
364	ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV
365
366	movq	%rsp, %rdi
367	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
368
369	pushq	6*8(%rdi)		/* regs->ss */
370	pushq	5*8(%rdi)		/* regs->rsp */
371	pushq	4*8(%rdi)		/* regs->eflags */
372	pushq	3*8(%rdi)		/* regs->cs */
373	pushq	2*8(%rdi)		/* regs->ip */
374	pushq	1*8(%rdi)		/* regs->orig_ax */
375	pushq	(%rdi)			/* pt_regs->di */
376.Lint80_keep_stack:
377
378	pushq	%rsi			/* pt_regs->si */
379	xorl	%esi, %esi		/* nospec   si */
380	pushq	%rdx			/* pt_regs->dx */
381	xorl	%edx, %edx		/* nospec   dx */
382	pushq	%rcx			/* pt_regs->cx */
383	xorl	%ecx, %ecx		/* nospec   cx */
384	pushq	$-ENOSYS		/* pt_regs->ax */
385	pushq   %r8			/* pt_regs->r8 */
386	xorl	%r8d, %r8d		/* nospec   r8 */
387	pushq   %r9			/* pt_regs->r9 */
388	xorl	%r9d, %r9d		/* nospec   r9 */
389	pushq   %r10			/* pt_regs->r10*/
390	xorl	%r10d, %r10d		/* nospec   r10 */
391	pushq   %r11			/* pt_regs->r11 */
392	xorl	%r11d, %r11d		/* nospec   r11 */
393	pushq   %rbx                    /* pt_regs->rbx */
394	xorl	%ebx, %ebx		/* nospec   rbx */
395	pushq   %rbp                    /* pt_regs->rbp */
396	xorl	%ebp, %ebp		/* nospec   rbp */
397	pushq   %r12                    /* pt_regs->r12 */
398	xorl	%r12d, %r12d		/* nospec   r12 */
399	pushq   %r13                    /* pt_regs->r13 */
400	xorl	%r13d, %r13d		/* nospec   r13 */
401	pushq   %r14                    /* pt_regs->r14 */
402	xorl	%r14d, %r14d		/* nospec   r14 */
403	pushq   %r15                    /* pt_regs->r15 */
404	xorl	%r15d, %r15d		/* nospec   r15 */
405
406	UNWIND_HINT_REGS
407
408	cld
409
410	movq	%rsp, %rdi
411	call	do_int80_syscall_32
412	jmp	swapgs_restore_regs_and_return_to_usermode
413SYM_CODE_END(entry_INT80_compat)
414