arch/x86/entry/entry_64_compat.S - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Compatibility mode system call entry point for x86-64.
  *
  * Copyright 2000-2002 Andi Kleen, SuSE Labs.
  */
 #include <asm/asm-offsets.h>
 #include <asm/current.h>
 #include <asm/errno.h>
 #include <asm/thread_info.h>
 #include <asm/segment.h>
 #include <asm/irqflags.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
 #include <asm/nospec-branch.h>
 #include <linux/linkage.h>
 #include <linux/err.h>

 #include "calling.h"

 	.section .entry.text, "ax"

 /*
  * 32-bit SYSENTER entry.
  *
  * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
  * on 64-bit kernels running on Intel CPUs.
  *
  * The SYSENTER instruction, in principle, should *only* occur in the
  * vDSO.  In practice, a small number of Android devices were shipped
  * with a copy of Bionic that inlined a SYSENTER instruction.  This
  * never happened in any of Google's Bionic versions -- it only happened
  * in a narrow range of Intel-provided versions.
  *
  * SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
  * IF and VM in RFLAGS are cleared (IOW: interrupts are off).
  * SYSENTER does not save anything on the stack,
  * and does not save old RIP (!!!), RSP, or RFLAGS.
  *
  * Arguments:
  * eax  system call number
  * ebx  arg1
  * ecx  arg2
  * edx  arg3
  * esi  arg4
  * edi  arg5
  * ebp  user stack
  * 0(%ebp) arg6
  */
 SYM_CODE_START(entry_SYSENTER_compat)
 	UNWIND_HINT_ENTRY
 	ENDBR
 	/* Interrupts are off on entry. */
 	swapgs

 	pushq	%rax
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
 	popq	%rax

 	movq	PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp

 	/* Construct struct pt_regs on stack */
 	pushq	$__USER_DS		/* pt_regs->ss */
 	pushq	$0			/* pt_regs->sp = 0 (placeholder) */

 	/*
 	 * Push flags.  This is nasty.  First, interrupts are currently
 	 * off, but we need pt_regs->flags to have IF set.  Second, if TS
 	 * was set in usermode, it's still set, and we're singlestepping
 	 * through this code.  do_SYSENTER_32() will fix up IF.
 	 */
 	pushfq				/* pt_regs->flags (except IF = 0) */
 	pushq	$__USER32_CS		/* pt_regs->cs */
 	pushq	$0			/* pt_regs->ip = 0 (placeholder) */
 SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)

 	/*
 	 * User tracing code (ptrace or signal handlers) might assume that
 	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
 	 * syscall.  Just in case the high bits are nonzero, zero-extend
 	 * the syscall number.  (This could almost certainly be deleted
 	 * with no ill effects.)
 	 */
 	movl	%eax, %eax

 	pushq	%rax			/* pt_regs->orig_ax */
 	PUSH_AND_CLEAR_REGS rax=$-ENOSYS
 	UNWIND_HINT_REGS

 	cld

 	/*
 	 * SYSENTER doesn't filter flags, so we need to clear NT and AC
 	 * ourselves.  To save a few cycles, we can check whether
 	 * either was set instead of doing an unconditional popfq.
 	 * This needs to happen before enabling interrupts so that
 	 * we don't get preempted with NT set.
 	 *
 	 * If TF is set, we will single-step all the way to here -- do_debug
 	 * will ignore all the traps.  (Yes, this is slow, but so is
 	 * single-stepping in general.  This allows us to avoid having
 	 * a more complicated code to handle the case where a user program
 	 * forces us to single-step through the SYSENTER entry code.)
 	 *
 	 * NB.: .Lsysenter_fix_flags is a label with the code under it moved
 	 * out-of-line as an optimization: NT is unlikely to be set in the
 	 * majority of the cases and instead of polluting the I$ unnecessarily,
 	 * we're keeping that code behind a branch which will predict as
 	 * not-taken and therefore its instructions won't be fetched.
 	 */
 	testl	$X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, EFLAGS(%rsp)
 	jnz	.Lsysenter_fix_flags
 .Lsysenter_flags_fixed:

 	/*
 	 * CPU bugs mitigations mechanisms can call other functions. They
 	 * should be invoked after making sure TF is cleared because
 	 * single-step is ignored only for instructions inside the
 	 * entry_SYSENTER_compat function.
 	 */
 	IBRS_ENTER
 	UNTRAIN_RET
 	CLEAR_BRANCH_HISTORY

 	movq	%rsp, %rdi
 	call	do_SYSENTER_32
 	jmp	sysret32_from_system_call

 .Lsysenter_fix_flags:
 	pushq	$X86_EFLAGS_FIXED
 	popfq
 	jmp	.Lsysenter_flags_fixed
 SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
 SYM_CODE_END(entry_SYSENTER_compat)

 /*
  * 32-bit SYSCALL entry.
  *
  * 32-bit system calls through the vDSO's __kernel_vsyscall enter here
  * on 64-bit kernels running on AMD CPUs.
  *
  * The SYSCALL instruction, in principle, should *only* occur in the
  * vDSO.  In practice, it appears that this really is the case.
  * As evidence:
  *
  *  - The calling convention for SYSCALL has changed several times without
  *    anyone noticing.
  *
  *  - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
  *    user task that did SYSCALL without immediately reloading SS
  *    would randomly crash.
  *
  *  - Most programmers do not directly target AMD CPUs, and the 32-bit
  *    SYSCALL instruction does not exist on Intel CPUs.  Even on AMD
  *    CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
  *    because the SYSCALL instruction in legacy/native 32-bit mode (as
  *    opposed to compat mode) is sufficiently poorly designed as to be
  *    essentially unusable.
  *
  * 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
  * RFLAGS to R11, then loads new SS, CS, and RIP from previously
  * programmed MSRs.  RFLAGS gets masked by a value from another MSR
  * (so CLD and CLAC are not needed).  SYSCALL does not save anything on
  * the stack and does not change RSP.
  *
  * Note: RFLAGS saving+masking-with-MSR happens only in Long mode
  * (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
  * Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
  * (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
  * or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
  *
  * Arguments:
  * eax  system call number
  * ecx  return address
  * ebx  arg1
  * ebp  arg2	(note: not saved in the stack frame, should not be touched)
  * edx  arg3
  * esi  arg4
  * edi  arg5
  * esp  user stack
  * 0(%esp) arg6
  */
 SYM_CODE_START(entry_SYSCALL_compat)
 	UNWIND_HINT_ENTRY
 	ENDBR
 	/* Interrupts are off on entry. */
 	swapgs

 	/* Stash user ESP */
 	movl	%esp, %r8d

 	/* Use %rsp as scratch reg. User ESP is stashed in r8 */
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp

 	/* Switch to the kernel stack */
 	movq	PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp

 SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR

 	/* Construct struct pt_regs on stack */
 	pushq	$__USER_DS		/* pt_regs->ss */
 	pushq	%r8			/* pt_regs->sp */
 	pushq	%r11			/* pt_regs->flags */
 	pushq	$__USER32_CS		/* pt_regs->cs */
 	pushq	%rcx			/* pt_regs->ip */
 SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
 	movl	%eax, %eax		/* discard orig_ax high bits */
 	pushq	%rax			/* pt_regs->orig_ax */
 	PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS
 	UNWIND_HINT_REGS

 	IBRS_ENTER
 	UNTRAIN_RET
 	CLEAR_BRANCH_HISTORY

 	movq	%rsp, %rdi
 	call	do_fast_syscall_32

 sysret32_from_system_call:
 	/* XEN PV guests always use IRET path */
 	ALTERNATIVE "testb %al, %al; jz swapgs_restore_regs_and_return_to_usermode", \
 		    "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV

 	/*
 	 * Opportunistic SYSRET
 	 *
 	 * We are not going to return to userspace from the trampoline
 	 * stack. So let's erase the thread stack right now.
 	 */
 	STACKLEAK_ERASE

 	IBRS_EXIT

 	movq	RBX(%rsp), %rbx		/* pt_regs->rbx */
 	movq	RBP(%rsp), %rbp		/* pt_regs->rbp */
 	movq	EFLAGS(%rsp), %r11	/* pt_regs->flags (in r11) */
 	movq	RIP(%rsp), %rcx		/* pt_regs->ip (in rcx) */
 	addq	$RAX, %rsp		/* Skip r8-r15 */
 	popq	%rax			/* pt_regs->rax */
 	popq	%rdx			/* Skip pt_regs->cx */
 	popq	%rdx			/* pt_regs->dx */
 	popq	%rsi			/* pt_regs->si */
 	popq	%rdi			/* pt_regs->di */

         /*
          * USERGS_SYSRET32 does:
          *  GSBASE = user's GS base
          *  EIP = ECX
          *  RFLAGS = R11
          *  CS = __USER32_CS
          *  SS = __USER_DS
          *
 	 * ECX will not match pt_regs->cx, but we're returning to a vDSO
 	 * trampoline that will fix up RCX, so this is okay.
 	 *
 	 * R12-R15 are callee-saved, so they contain whatever was in them
 	 * when the system call started, which is already known to user
 	 * code.  We zero R8-R10 to avoid info leaks.
          */
 	movq	RSP-ORIG_RAX(%rsp), %rsp
 SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR

 	/*
 	 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
 	 * on the process stack which is not mapped to userspace and
 	 * not readable after we SWITCH_TO_USER_CR3.  Delay the CR3
 	 * switch until after after the last reference to the process
 	 * stack.
 	 *
 	 * %r8/%r9 are zeroed before the sysret, thus safe to clobber.
 	 */
 	SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9

 	xorl	%r8d, %r8d
 	xorl	%r9d, %r9d
 	xorl	%r10d, %r10d
 	swapgs
 	CLEAR_CPU_BUFFERS
 	sysretl
 SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	int3
 SYM_CODE_END(entry_SYSCALL_compat)

 /*
  * int 0x80 is used by 32 bit mode as a system call entry. Normally idt entries
  * point to C routines, however since this is a system call interface the branch
  * history needs to be scrubbed to protect against BHI attacks, and that
  * scrubbing needs to take place in assembly code prior to entering any C
  * routines.
  */
 SYM_CODE_START(int80_emulation)
 	ANNOTATE_NOENDBR
 	UNWIND_HINT_FUNC
 	CLEAR_BRANCH_HISTORY
 	jmp do_int80_emulation
 SYM_CODE_END(int80_emulation)
	/* SPDX-License-Identifier: GPL-2.0 */
	/*
	* Compatibility mode system call entry point for x86-64.
	*
	* Copyright 2000-2002 Andi Kleen, SuSE Labs.
	*/
	#include <asm/asm-offsets.h>
	#include <asm/current.h>
	#include <asm/errno.h>
	#include <asm/thread_info.h>
	#include <asm/segment.h>
	#include <asm/irqflags.h>
	#include <asm/asm.h>
	#include <asm/smap.h>
	#include <asm/nospec-branch.h>
	#include <linux/linkage.h>
	#include <linux/err.h>

	#include "calling.h"

	.section .entry.text, "ax"

	/*
	* 32-bit SYSENTER entry.
	*
	* 32-bit system calls through the vDSO's __kernel_vsyscall enter here
	* on 64-bit kernels running on Intel CPUs.
	*
	* The SYSENTER instruction, in principle, should only occur in the
	* vDSO. In practice, a small number of Android devices were shipped
	* with a copy of Bionic that inlined a SYSENTER instruction. This
	* never happened in any of Google's Bionic versions -- it only happened
	* in a narrow range of Intel-provided versions.
	*
	* SYSENTER loads SS, RSP, CS, and RIP from previously programmed MSRs.
	* IF and VM in RFLAGS are cleared (IOW: interrupts are off).
	* SYSENTER does not save anything on the stack,
	* and does not save old RIP (!!!), RSP, or RFLAGS.
	*
	* Arguments:
	* eax system call number
	* ebx arg1
	* ecx arg2
	* edx arg3
	* esi arg4
	* edi arg5
	* ebp user stack
	* 0(%ebp) arg6
	*/
	SYM_CODE_START(entry_SYSENTER_compat)
	UNWIND_HINT_ENTRY
	ENDBR
	/* Interrupts are off on entry. */
	swapgs

	pushq %rax
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
	popq %rax

	movq PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp

	/* Construct struct pt_regs on stack */
	pushq $__USER_DS /* pt_regs->ss */
	pushq $0 /* pt_regs->sp = 0 (placeholder) */

	/*
	* Push flags. This is nasty. First, interrupts are currently
	* off, but we need pt_regs->flags to have IF set. Second, if TS
	* was set in usermode, it's still set, and we're singlestepping
	* through this code. do_SYSENTER_32() will fix up IF.
	*/
	pushfq /* pt_regs->flags (except IF = 0) */
	pushq $__USER32_CS /* pt_regs->cs */
	pushq $0 /* pt_regs->ip = 0 (placeholder) */
	SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)

	/*
	* User tracing code (ptrace or signal handlers) might assume that
	* the saved RAX contains a 32-bit number when we're invoking a 32-bit
	* syscall. Just in case the high bits are nonzero, zero-extend
	* the syscall number. (This could almost certainly be deleted
	* with no ill effects.)
	*/
	movl %eax, %eax

	pushq %rax /* pt_regs->orig_ax */
	PUSH_AND_CLEAR_REGS rax=$-ENOSYS
	UNWIND_HINT_REGS

	cld

	/*
	* SYSENTER doesn't filter flags, so we need to clear NT and AC
	* ourselves. To save a few cycles, we can check whether
	* either was set instead of doing an unconditional popfq.
	* This needs to happen before enabling interrupts so that
	* we don't get preempted with NT set.
	*
	* If TF is set, we will single-step all the way to here -- do_debug
	* will ignore all the traps. (Yes, this is slow, but so is
	* single-stepping in general. This allows us to avoid having
	* a more complicated code to handle the case where a user program
	* forces us to single-step through the SYSENTER entry code.)
	*
	* NB.: .Lsysenter_fix_flags is a label with the code under it moved
	* out-of-line as an optimization: NT is unlikely to be set in the
	* majority of the cases and instead of polluting the I$ unnecessarily,
	* we're keeping that code behind a branch which will predict as
	* not-taken and therefore its instructions won't be fetched.
	*/
	testl $X86_EFLAGS_NT\|X86_EFLAGS_AC\|X86_EFLAGS_TF, EFLAGS(%rsp)
	jnz .Lsysenter_fix_flags
	.Lsysenter_flags_fixed:

	/*
	* CPU bugs mitigations mechanisms can call other functions. They
	* should be invoked after making sure TF is cleared because
	* single-step is ignored only for instructions inside the
	* entry_SYSENTER_compat function.
	*/
	IBRS_ENTER
	UNTRAIN_RET
	CLEAR_BRANCH_HISTORY

	movq %rsp, %rdi
	call do_SYSENTER_32
	jmp sysret32_from_system_call

	.Lsysenter_fix_flags:
	pushq $X86_EFLAGS_FIXED
	popfq
	jmp .Lsysenter_flags_fixed
	SYM_INNER_LABEL(__end_entry_SYSENTER_compat, SYM_L_GLOBAL)
	SYM_CODE_END(entry_SYSENTER_compat)

	/*
	* 32-bit SYSCALL entry.
	*
	* 32-bit system calls through the vDSO's __kernel_vsyscall enter here
	* on 64-bit kernels running on AMD CPUs.
	*
	* The SYSCALL instruction, in principle, should only occur in the
	* vDSO. In practice, it appears that this really is the case.
	* As evidence:
	*
	* - The calling convention for SYSCALL has changed several times without
	* anyone noticing.
	*
	* - Prior to the in-kernel X86_BUG_SYSRET_SS_ATTRS fixup, anything
	* user task that did SYSCALL without immediately reloading SS
	* would randomly crash.
	*
	* - Most programmers do not directly target AMD CPUs, and the 32-bit
	* SYSCALL instruction does not exist on Intel CPUs. Even on AMD
	* CPUs, Linux disables the SYSCALL instruction on 32-bit kernels
	* because the SYSCALL instruction in legacy/native 32-bit mode (as
	* opposed to compat mode) is sufficiently poorly designed as to be
	* essentially unusable.
	*
	* 32-bit SYSCALL saves RIP to RCX, clears RFLAGS.RF, then saves
	* RFLAGS to R11, then loads new SS, CS, and RIP from previously
	* programmed MSRs. RFLAGS gets masked by a value from another MSR
	* (so CLD and CLAC are not needed). SYSCALL does not save anything on
	* the stack and does not change RSP.
	*
	* Note: RFLAGS saving+masking-with-MSR happens only in Long mode
	* (in legacy 32-bit mode, IF, RF and VM bits are cleared and that's it).
	* Don't get confused: RFLAGS saving+masking depends on Long Mode Active bit
	* (EFER.LMA=1), NOT on bitness of userspace where SYSCALL executes
	* or target CS descriptor's L bit (SYSCALL does not read segment descriptors).
	*
	* Arguments:
	* eax system call number
	* ecx return address
	* ebx arg1
	* ebp arg2 (note: not saved in the stack frame, should not be touched)
	* edx arg3
	* esi arg4
	* edi arg5
	* esp user stack
	* 0(%esp) arg6
	*/
	SYM_CODE_START(entry_SYSCALL_compat)
	UNWIND_HINT_ENTRY
	ENDBR
	/* Interrupts are off on entry. */
	swapgs

	/* Stash user ESP */
	movl %esp, %r8d

	/* Use %rsp as scratch reg. User ESP is stashed in r8 */
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp

	/* Switch to the kernel stack */
	movq PER_CPU_VAR(pcpu_hot + X86_top_of_stack), %rsp

	SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR

	/* Construct struct pt_regs on stack */
	pushq $__USER_DS /* pt_regs->ss */
	pushq %r8 /* pt_regs->sp */
	pushq %r11 /* pt_regs->flags */
	pushq $__USER32_CS /* pt_regs->cs */
	pushq %rcx /* pt_regs->ip */
	SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
	movl %eax, %eax /* discard orig_ax high bits */
	pushq %rax /* pt_regs->orig_ax */
	PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS
	UNWIND_HINT_REGS

	IBRS_ENTER
	UNTRAIN_RET
	CLEAR_BRANCH_HISTORY

	movq %rsp, %rdi
	call do_fast_syscall_32

	sysret32_from_system_call:
	/* XEN PV guests always use IRET path */
	ALTERNATIVE "testb %al, %al; jz swapgs_restore_regs_and_return_to_usermode", \
	"jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV

	/*
	* Opportunistic SYSRET
	*
	* We are not going to return to userspace from the trampoline
	* stack. So let's erase the thread stack right now.
	*/
	STACKLEAK_ERASE

	IBRS_EXIT

	movq RBX(%rsp), %rbx /* pt_regs->rbx */
	movq RBP(%rsp), %rbp /* pt_regs->rbp */
	movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
	movq RIP(%rsp), %rcx /* pt_regs->ip (in rcx) */
	addq $RAX, %rsp /* Skip r8-r15 */
	popq %rax /* pt_regs->rax */
	popq %rdx /* Skip pt_regs->cx */
	popq %rdx /* pt_regs->dx */
	popq %rsi /* pt_regs->si */
	popq %rdi /* pt_regs->di */

	/*
	* USERGS_SYSRET32 does:
	* GSBASE = user's GS base
	* EIP = ECX
	* RFLAGS = R11
	* CS = __USER32_CS
	* SS = __USER_DS
	*
	* ECX will not match pt_regs->cx, but we're returning to a vDSO
	* trampoline that will fix up RCX, so this is okay.
	*
	* R12-R15 are callee-saved, so they contain whatever was in them
	* when the system call started, which is already known to user
	* code. We zero R8-R10 to avoid info leaks.
	*/
	movq RSP-ORIG_RAX(%rsp), %rsp
	SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR

	/*
	* The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
	* on the process stack which is not mapped to userspace and
	* not readable after we SWITCH_TO_USER_CR3. Delay the CR3
	* switch until after after the last reference to the process
	* stack.
	*
	* %r8/%r9 are zeroed before the sysret, thus safe to clobber.
	*/
	SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9

	xorl %r8d, %r8d
	xorl %r9d, %r9d
	xorl %r10d, %r10d
	swapgs
	CLEAR_CPU_BUFFERS
	sysretl
	SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	int3
	SYM_CODE_END(entry_SYSCALL_compat)

	/*
	* int 0x80 is used by 32 bit mode as a system call entry. Normally idt entries
	* point to C routines, however since this is a system call interface the branch
	* history needs to be scrubbed to protect against BHI attacks, and that
	* scrubbing needs to take place in assembly code prior to entering any C
	* routines.
	*/
	SYM_CODE_START(int80_emulation)
	ANNOTATE_NOENDBR
	UNWIND_HINT_FUNC
	CLEAR_BRANCH_HISTORY
	jmp do_int80_emulation
	SYM_CODE_END(int80_emulation)