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281 lines
7.6 KiB
281 lines
7.6 KiB
// 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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__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs) |
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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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if (likely(nr < NR_syscalls)) { |
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nr = array_index_nospec(nr, NR_syscalls); |
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regs->ax = sys_call_table[nr](regs); |
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#ifdef CONFIG_X86_X32_ABI |
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} else if (likely((nr & __X32_SYSCALL_BIT) && |
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(nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) { |
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nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT, |
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X32_NR_syscalls); |
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regs->ax = x32_sys_call_table[nr](regs); |
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#endif |
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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 unsigned 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 (unsigned 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, |
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unsigned int nr) |
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{ |
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if (likely(nr < IA32_NR_syscalls)) { |
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nr = array_index_nospec(nr, IA32_NR_syscalls); |
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regs->ax = ia32_sys_call_table[nr](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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unsigned int nr = syscall_32_enter(regs); |
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/* |
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* Subtlety here: if ptrace pokes something larger than 2^32-1 into |
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* orig_ax, the unsigned int return value truncates it. This may |
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* or may not be necessary, but it matches the old asm behavior. |
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*/ |
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nr = (unsigned int)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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unsigned int nr = syscall_32_enter(regs); |
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int res; |
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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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instrumentation_end(); |
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local_irq_disable(); |
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irqentry_exit_to_user_mode(regs); |
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return false; |
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} |
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/* The case truncates any ptrace induced syscall nr > 2^32 -1 */ |
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nr = (unsigned int)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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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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instrumentation_begin(); |
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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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irqentry_exit(regs, state); |
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} |
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} |
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#endif /* CONFIG_XEN_PV */
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