| /* 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/ia32_unistd.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(cpu_current_top_of_stack), %rsp |
| |
| /* Construct struct pt_regs on stack */ |
| pushq $__USER32_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 |
| |
| IBRS_ENTER |
| UNTRAIN_RET |
| |
| /* |
| * 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: |
| |
| movq %rsp, %rdi |
| call do_SYSENTER_32 |
| /* XEN PV guests always use IRET path */ |
| ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ |
| "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV |
| 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) |
| ANNOTATE_NOENDBR // is_sysenter_singlestep |
| 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(cpu_current_top_of_stack), %rsp |
| |
| SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR |
| |
| /* Construct struct pt_regs on stack */ |
| pushq $__USER32_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 |
| |
| movq %rsp, %rdi |
| call do_fast_syscall_32 |
| /* XEN PV guests always use IRET path */ |
| ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \ |
| "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV |
| |
| /* Opportunistic SYSRET */ |
| sysret32_from_system_call: |
| /* |
| * 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 |
| sysretl |
| SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL) |
| ANNOTATE_NOENDBR |
| int3 |
| SYM_CODE_END(entry_SYSCALL_compat) |
| |
| /* |
| * 32-bit legacy system call entry. |
| * |
| * 32-bit x86 Linux system calls traditionally used the INT $0x80 |
| * instruction. INT $0x80 lands here. |
| * |
| * This entry point can be used by 32-bit and 64-bit programs to perform |
| * 32-bit system calls. Instances of INT $0x80 can be found inline in |
| * various programs and libraries. It is also used by the vDSO's |
| * __kernel_vsyscall fallback for hardware that doesn't support a faster |
| * entry method. Restarted 32-bit system calls also fall back to INT |
| * $0x80 regardless of what instruction was originally used to do the |
| * system call. |
| * |
| * This is considered a slow path. It is not used by most libc |
| * implementations on modern hardware except during process startup. |
| * |
| * Arguments: |
| * eax system call number |
| * ebx arg1 |
| * ecx arg2 |
| * edx arg3 |
| * esi arg4 |
| * edi arg5 |
| * ebp arg6 |
| */ |
| SYM_CODE_START(entry_INT80_compat) |
| UNWIND_HINT_ENTRY |
| ENDBR |
| /* |
| * Interrupts are off on entry. |
| */ |
| ASM_CLAC /* Do this early to minimize exposure */ |
| SWAPGS |
| |
| /* |
| * User tracing code (ptrace or signal handlers) might assume that |
| * the saved RAX contains a 32-bit number when we're invoking a 32-bit |
| * syscall. Just in case the high bits are nonzero, zero-extend |
| * the syscall number. (This could almost certainly be deleted |
| * with no ill effects.) |
| */ |
| movl %eax, %eax |
| |
| /* switch to thread stack expects orig_ax and rdi to be pushed */ |
| pushq %rax /* pt_regs->orig_ax */ |
| |
| /* Need to switch before accessing the thread stack. */ |
| SWITCH_TO_KERNEL_CR3 scratch_reg=%rax |
| |
| /* In the Xen PV case we already run on the thread stack. */ |
| ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV |
| |
| movq %rsp, %rax |
| movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp |
| |
| pushq 5*8(%rax) /* regs->ss */ |
| pushq 4*8(%rax) /* regs->rsp */ |
| pushq 3*8(%rax) /* regs->eflags */ |
| pushq 2*8(%rax) /* regs->cs */ |
| pushq 1*8(%rax) /* regs->ip */ |
| pushq 0*8(%rax) /* regs->orig_ax */ |
| .Lint80_keep_stack: |
| |
| PUSH_AND_CLEAR_REGS rax=$-ENOSYS |
| UNWIND_HINT_REGS |
| |
| cld |
| |
| IBRS_ENTER |
| UNTRAIN_RET |
| |
| movq %rsp, %rdi |
| call do_int80_syscall_32 |
| jmp swapgs_restore_regs_and_return_to_usermode |
| SYM_CODE_END(entry_INT80_compat) |
