321 lines
8.3 KiB
C
321 lines
8.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* common.c - C code for kernel entry and exit
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* Copyright (c) 2015 Andrew Lutomirski
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*
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* Based on asm and ptrace code by many authors. The code here originated
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* in ptrace.c and signal.c.
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*/
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/sched/task_stack.h>
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#include <linux/entry-common.h>
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#include <linux/mm.h>
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#include <linux/smp.h>
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#include <linux/errno.h>
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#include <linux/ptrace.h>
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#include <linux/export.h>
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#include <linux/nospec.h>
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#include <linux/syscalls.h>
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#include <linux/uaccess.h>
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#ifdef CONFIG_XEN_PV
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#include <xen/xen-ops.h>
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#include <xen/events.h>
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#endif
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#include <asm/desc.h>
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#include <asm/traps.h>
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#include <asm/vdso.h>
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#include <asm/cpufeature.h>
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#include <asm/fpu/api.h>
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#include <asm/nospec-branch.h>
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#include <asm/io_bitmap.h>
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#include <asm/syscall.h>
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#include <asm/irq_stack.h>
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#ifdef CONFIG_X86_64
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static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr)
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{
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/*
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* Convert negative numbers to very high and thus out of range
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* numbers for comparisons.
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*/
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unsigned int unr = nr;
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if (likely(unr < NR_syscalls)) {
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unr = array_index_nospec(unr, NR_syscalls);
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regs->ax = sys_call_table[unr](regs);
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return true;
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}
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return false;
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}
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static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
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{
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/*
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* Adjust the starting offset of the table, and convert numbers
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* < __X32_SYSCALL_BIT to very high and thus out of range
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* numbers for comparisons.
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*/
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unsigned int xnr = nr - __X32_SYSCALL_BIT;
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if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) {
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xnr = array_index_nospec(xnr, X32_NR_syscalls);
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regs->ax = x32_sys_call_table[xnr](regs);
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return true;
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}
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return false;
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}
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__visible noinstr void do_syscall_64(struct pt_regs *regs, int nr)
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{
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add_random_kstack_offset();
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nr = syscall_enter_from_user_mode(regs, nr);
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instrumentation_begin();
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if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
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/* Invalid system call, but still a system call. */
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regs->ax = __x64_sys_ni_syscall(regs);
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}
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instrumentation_end();
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syscall_exit_to_user_mode(regs);
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}
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#endif
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#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
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static __always_inline int syscall_32_enter(struct pt_regs *regs)
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{
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if (IS_ENABLED(CONFIG_IA32_EMULATION))
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current_thread_info()->status |= TS_COMPAT;
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return (int)regs->orig_ax;
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}
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/*
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* Invoke a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL.
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*/
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static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
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{
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/*
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* Convert negative numbers to very high and thus out of range
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* numbers for comparisons.
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*/
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unsigned int unr = nr;
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if (likely(unr < IA32_NR_syscalls)) {
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unr = array_index_nospec(unr, IA32_NR_syscalls);
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regs->ax = ia32_sys_call_table[unr](regs);
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} else if (nr != -1) {
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regs->ax = __ia32_sys_ni_syscall(regs);
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}
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}
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/* Handles int $0x80 */
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__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
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{
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int nr = syscall_32_enter(regs);
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add_random_kstack_offset();
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/*
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* Subtlety here: if ptrace pokes something larger than 2^31-1 into
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* orig_ax, the int return value truncates it. This matches
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* the semantics of syscall_get_nr().
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*/
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nr = syscall_enter_from_user_mode(regs, nr);
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instrumentation_begin();
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do_syscall_32_irqs_on(regs, nr);
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instrumentation_end();
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syscall_exit_to_user_mode(regs);
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}
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static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
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{
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int nr = syscall_32_enter(regs);
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int res;
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add_random_kstack_offset();
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/*
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* This cannot use syscall_enter_from_user_mode() as it has to
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* fetch EBP before invoking any of the syscall entry work
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* functions.
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*/
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syscall_enter_from_user_mode_prepare(regs);
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instrumentation_begin();
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/* Fetch EBP from where the vDSO stashed it. */
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if (IS_ENABLED(CONFIG_X86_64)) {
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/*
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* Micro-optimization: the pointer we're following is
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* explicitly 32 bits, so it can't be out of range.
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*/
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res = __get_user(*(u32 *)®s->bp,
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(u32 __user __force *)(unsigned long)(u32)regs->sp);
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} else {
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res = get_user(*(u32 *)®s->bp,
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(u32 __user __force *)(unsigned long)(u32)regs->sp);
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}
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if (res) {
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/* User code screwed up. */
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regs->ax = -EFAULT;
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local_irq_disable();
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instrumentation_end();
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irqentry_exit_to_user_mode(regs);
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return false;
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}
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nr = syscall_enter_from_user_mode_work(regs, nr);
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/* Now this is just like a normal syscall. */
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do_syscall_32_irqs_on(regs, nr);
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instrumentation_end();
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syscall_exit_to_user_mode(regs);
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return true;
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}
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/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
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__visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
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{
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/*
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* Called using the internal vDSO SYSENTER/SYSCALL32 calling
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* convention. Adjust regs so it looks like we entered using int80.
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*/
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unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
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vdso_image_32.sym_int80_landing_pad;
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/*
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* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
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* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
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* Fix it up.
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*/
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regs->ip = landing_pad;
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/* Invoke the syscall. If it failed, keep it simple: use IRET. */
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if (!__do_fast_syscall_32(regs))
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return 0;
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#ifdef CONFIG_X86_64
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/*
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* Opportunistic SYSRETL: if possible, try to return using SYSRETL.
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* SYSRETL is available on all 64-bit CPUs, so we don't need to
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* bother with SYSEXIT.
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*
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* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
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* because the ECX fixup above will ensure that this is essentially
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* never the case.
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*/
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return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
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regs->ip == landing_pad &&
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(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
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#else
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/*
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* Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
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*
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* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
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* because the ECX fixup above will ensure that this is essentially
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* never the case.
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*
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* We don't allow syscalls at all from VM86 mode, but we still
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* need to check VM, because we might be returning from sys_vm86.
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*/
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return static_cpu_has(X86_FEATURE_SEP) &&
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regs->cs == __USER_CS && regs->ss == __USER_DS &&
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regs->ip == landing_pad &&
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(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
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#endif
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}
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/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
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__visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
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{
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/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
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regs->sp = regs->bp;
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/* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */
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regs->flags |= X86_EFLAGS_IF;
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return do_fast_syscall_32(regs);
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}
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#endif
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SYSCALL_DEFINE0(ni_syscall)
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{
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return -ENOSYS;
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}
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#ifdef CONFIG_XEN_PV
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#ifndef CONFIG_PREEMPTION
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/*
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* Some hypercalls issued by the toolstack can take many 10s of
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* seconds. Allow tasks running hypercalls via the privcmd driver to
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* be voluntarily preempted even if full kernel preemption is
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* disabled.
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*
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* Such preemptible hypercalls are bracketed by
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* xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
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* calls.
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*/
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DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
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EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
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/*
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* In case of scheduling the flag must be cleared and restored after
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* returning from schedule as the task might move to a different CPU.
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*/
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static __always_inline bool get_and_clear_inhcall(void)
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{
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bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);
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__this_cpu_write(xen_in_preemptible_hcall, false);
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return inhcall;
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}
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static __always_inline void restore_inhcall(bool inhcall)
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{
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__this_cpu_write(xen_in_preemptible_hcall, inhcall);
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}
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#else
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static __always_inline bool get_and_clear_inhcall(void) { return false; }
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static __always_inline void restore_inhcall(bool inhcall) { }
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#endif
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static void __xen_pv_evtchn_do_upcall(struct pt_regs *regs)
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{
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struct pt_regs *old_regs = set_irq_regs(regs);
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inc_irq_stat(irq_hv_callback_count);
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xen_hvm_evtchn_do_upcall();
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set_irq_regs(old_regs);
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}
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__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
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{
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irqentry_state_t state = irqentry_enter(regs);
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bool inhcall;
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instrumentation_begin();
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run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);
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inhcall = get_and_clear_inhcall();
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if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
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irqentry_exit_cond_resched();
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instrumentation_end();
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restore_inhcall(inhcall);
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} else {
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instrumentation_end();
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irqentry_exit(regs, state);
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}
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}
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#endif /* CONFIG_XEN_PV */
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