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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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9999c8c01f
Now that slow-path syscalls always enter C before enabling interrupts, it's straightforward to call enter_from_user_mode() before enabling interrupts rather than doing it as part of entry tracing. With this change, we should finally be able to retire exception_enter(). This will also enable optimizations based on knowing that we never change context tracking state with interrupts on. Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Frédéric Weisbecker <fweisbec@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/bc376ecf87921a495e874ff98139b1ca2f5c5dd7.1457558566.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
487 lines
13 KiB
C
487 lines
13 KiB
C
/*
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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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* GPL v2
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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/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/tracehook.h>
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#include <linux/audit.h>
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#include <linux/seccomp.h>
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#include <linux/signal.h>
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#include <linux/export.h>
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#include <linux/context_tracking.h>
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#include <linux/user-return-notifier.h>
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#include <linux/uprobes.h>
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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/uaccess.h>
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#include <asm/cpufeature.h>
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#define CREATE_TRACE_POINTS
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#include <trace/events/syscalls.h>
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static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
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{
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unsigned long top_of_stack =
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(unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
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return (struct thread_info *)(top_of_stack - THREAD_SIZE);
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}
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#ifdef CONFIG_CONTEXT_TRACKING
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/* Called on entry from user mode with IRQs off. */
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__visible void enter_from_user_mode(void)
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{
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CT_WARN_ON(ct_state() != CONTEXT_USER);
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user_exit();
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}
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#else
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static inline void enter_from_user_mode(void) {}
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#endif
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static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
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{
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#ifdef CONFIG_X86_64
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if (arch == AUDIT_ARCH_X86_64) {
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audit_syscall_entry(regs->orig_ax, regs->di,
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regs->si, regs->dx, regs->r10);
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} else
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#endif
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{
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audit_syscall_entry(regs->orig_ax, regs->bx,
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regs->cx, regs->dx, regs->si);
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}
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}
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/*
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* We can return 0 to resume the syscall or anything else to go to phase
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* 2. If we resume the syscall, we need to put something appropriate in
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* regs->orig_ax.
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*
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* NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
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* are fully functional.
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*
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* For phase 2's benefit, our return value is:
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* 0: resume the syscall
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* 1: go to phase 2; no seccomp phase 2 needed
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* anything else: go to phase 2; pass return value to seccomp
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*/
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unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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unsigned long ret = 0;
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u32 work;
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if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
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BUG_ON(regs != task_pt_regs(current));
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work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
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#ifdef CONFIG_SECCOMP
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/*
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* Do seccomp first -- it should minimize exposure of other
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* code, and keeping seccomp fast is probably more valuable
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* than the rest of this.
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*/
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if (work & _TIF_SECCOMP) {
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struct seccomp_data sd;
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sd.arch = arch;
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sd.nr = regs->orig_ax;
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sd.instruction_pointer = regs->ip;
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#ifdef CONFIG_X86_64
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if (arch == AUDIT_ARCH_X86_64) {
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sd.args[0] = regs->di;
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sd.args[1] = regs->si;
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sd.args[2] = regs->dx;
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sd.args[3] = regs->r10;
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sd.args[4] = regs->r8;
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sd.args[5] = regs->r9;
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} else
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#endif
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{
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sd.args[0] = regs->bx;
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sd.args[1] = regs->cx;
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sd.args[2] = regs->dx;
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sd.args[3] = regs->si;
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sd.args[4] = regs->di;
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sd.args[5] = regs->bp;
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}
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BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
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BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);
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ret = seccomp_phase1(&sd);
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if (ret == SECCOMP_PHASE1_SKIP) {
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regs->orig_ax = -1;
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ret = 0;
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} else if (ret != SECCOMP_PHASE1_OK) {
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return ret; /* Go directly to phase 2 */
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}
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work &= ~_TIF_SECCOMP;
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}
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#endif
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/* Do our best to finish without phase 2. */
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if (work == 0)
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return ret; /* seccomp and/or nohz only (ret == 0 here) */
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#ifdef CONFIG_AUDITSYSCALL
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if (work == _TIF_SYSCALL_AUDIT) {
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/*
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* If there is no more work to be done except auditing,
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* then audit in phase 1. Phase 2 always audits, so, if
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* we audit here, then we can't go on to phase 2.
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*/
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do_audit_syscall_entry(regs, arch);
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return 0;
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}
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#endif
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return 1; /* Something is enabled that we can't handle in phase 1 */
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}
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/* Returns the syscall nr to run (which should match regs->orig_ax). */
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long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
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unsigned long phase1_result)
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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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long ret = 0;
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u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
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if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
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BUG_ON(regs != task_pt_regs(current));
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#ifdef CONFIG_SECCOMP
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/*
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* Call seccomp_phase2 before running the other hooks so that
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* they can see any changes made by a seccomp tracer.
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*/
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if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
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/* seccomp failures shouldn't expose any additional code. */
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return -1;
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}
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#endif
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if (unlikely(work & _TIF_SYSCALL_EMU))
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ret = -1L;
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if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
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tracehook_report_syscall_entry(regs))
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ret = -1L;
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if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
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trace_sys_enter(regs, regs->orig_ax);
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do_audit_syscall_entry(regs, arch);
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return ret ?: regs->orig_ax;
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}
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long syscall_trace_enter(struct pt_regs *regs)
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{
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u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
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unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);
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if (phase1_result == 0)
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return regs->orig_ax;
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else
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return syscall_trace_enter_phase2(regs, arch, phase1_result);
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}
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#define EXIT_TO_USERMODE_LOOP_FLAGS \
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(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
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_TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
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static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
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{
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/*
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* In order to return to user mode, we need to have IRQs off with
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* none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
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* _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags
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* can be set at any time on preemptable kernels if we have IRQs on,
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* so we need to loop. Disabling preemption wouldn't help: doing the
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* work to clear some of the flags can sleep.
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*/
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while (true) {
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/* We have work to do. */
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local_irq_enable();
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if (cached_flags & _TIF_NEED_RESCHED)
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schedule();
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if (cached_flags & _TIF_UPROBE)
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uprobe_notify_resume(regs);
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/* deal with pending signal delivery */
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if (cached_flags & _TIF_SIGPENDING)
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do_signal(regs);
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if (cached_flags & _TIF_NOTIFY_RESUME) {
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clear_thread_flag(TIF_NOTIFY_RESUME);
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tracehook_notify_resume(regs);
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}
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if (cached_flags & _TIF_USER_RETURN_NOTIFY)
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fire_user_return_notifiers();
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/* Disable IRQs and retry */
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local_irq_disable();
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cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
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if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
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break;
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}
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}
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/* Called with IRQs disabled. */
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__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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u32 cached_flags;
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if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
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local_irq_disable();
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lockdep_sys_exit();
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cached_flags = READ_ONCE(ti->flags);
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if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
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exit_to_usermode_loop(regs, cached_flags);
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#ifdef CONFIG_COMPAT
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/*
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* Compat syscalls set TS_COMPAT. Make sure we clear it before
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* returning to user mode. We need to clear it *after* signal
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* handling, because syscall restart has a fixup for compat
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* syscalls. The fixup is exercised by the ptrace_syscall_32
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* selftest.
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*/
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ti->status &= ~TS_COMPAT;
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#endif
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user_enter();
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}
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#define SYSCALL_EXIT_WORK_FLAGS \
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(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
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_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
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static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
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{
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bool step;
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audit_syscall_exit(regs);
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if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
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trace_sys_exit(regs, regs->ax);
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/*
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* If TIF_SYSCALL_EMU is set, we only get here because of
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* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
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* We already reported this syscall instruction in
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* syscall_trace_enter().
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*/
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step = unlikely(
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(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
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== _TIF_SINGLESTEP);
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if (step || cached_flags & _TIF_SYSCALL_TRACE)
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tracehook_report_syscall_exit(regs, step);
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}
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/*
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* Called with IRQs on and fully valid regs. Returns with IRQs off in a
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* state such that we can immediately switch to user mode.
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*/
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__visible inline void syscall_return_slowpath(struct pt_regs *regs)
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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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u32 cached_flags = READ_ONCE(ti->flags);
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CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
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if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
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WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
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local_irq_enable();
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/*
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* First do one-time work. If these work items are enabled, we
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* want to run them exactly once per syscall exit with IRQs on.
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*/
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if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
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syscall_slow_exit_work(regs, cached_flags);
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local_irq_disable();
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prepare_exit_to_usermode(regs);
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}
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#ifdef CONFIG_X86_64
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__visible void do_syscall_64(struct pt_regs *regs)
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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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unsigned long nr = regs->orig_ax;
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enter_from_user_mode();
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local_irq_enable();
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if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
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nr = syscall_trace_enter(regs);
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/*
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* NB: Native and x32 syscalls are dispatched from the same
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* table. The only functional difference is the x32 bit in
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* regs->orig_ax, which changes the behavior of some syscalls.
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*/
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if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
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regs->ax = sys_call_table[nr & __SYSCALL_MASK](
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regs->di, regs->si, regs->dx,
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regs->r10, regs->r8, regs->r9);
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}
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syscall_return_slowpath(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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/*
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* Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
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* all entry and exit work and returns with IRQs off. This function is
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* extremely hot in workloads that use it, and it's usually called from
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* do_fast_syscall_32, so forcibly inline it to improve performance.
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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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{
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struct thread_info *ti = pt_regs_to_thread_info(regs);
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unsigned int nr = (unsigned int)regs->orig_ax;
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#ifdef CONFIG_IA32_EMULATION
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ti->status |= TS_COMPAT;
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#endif
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if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
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/*
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* Subtlety here: if ptrace pokes something larger than
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* 2^32-1 into orig_ax, this truncates it. This may or
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* may not be necessary, but it matches the old asm
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* behavior.
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*/
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nr = syscall_trace_enter(regs);
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}
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if (likely(nr < IA32_NR_syscalls)) {
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/*
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* It's possible that a 32-bit syscall implementation
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* takes a 64-bit parameter but nonetheless assumes that
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* the high bits are zero. Make sure we zero-extend all
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* of the args.
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*/
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regs->ax = ia32_sys_call_table[nr](
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(unsigned int)regs->bx, (unsigned int)regs->cx,
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(unsigned int)regs->dx, (unsigned int)regs->si,
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(unsigned int)regs->di, (unsigned int)regs->bp);
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}
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syscall_return_slowpath(regs);
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}
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/* Handles int $0x80 */
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__visible void do_int80_syscall_32(struct pt_regs *regs)
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{
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enter_from_user_mode();
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local_irq_enable();
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do_syscall_32_irqs_on(regs);
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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 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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enter_from_user_mode();
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local_irq_enable();
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/* Fetch EBP from where the vDSO stashed it. */
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if (
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#ifdef CONFIG_X86_64
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/*
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* Micro-optimization: the pointer we're following is explicitly
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* 32 bits, so it can't be out of range.
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*/
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__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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get_user(*(u32 *)®s->bp,
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(u32 __user __force *)(unsigned long)(u32)regs->sp)
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#endif
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) {
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/* User code screwed up. */
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local_irq_disable();
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regs->ax = -EFAULT;
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prepare_exit_to_usermode(regs);
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return 0; /* Keep it simple: use IRET. */
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}
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/* Now this is just like a normal syscall. */
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do_syscall_32_irqs_on(regs);
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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.
|
|
*
|
|
* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
|
|
* because the ECX fixup above will ensure that this is essentially
|
|
* never the case.
|
|
*
|
|
* We don't allow syscalls at all from VM86 mode, but we still
|
|
* need to check VM, because we might be returning from sys_vm86.
|
|
*/
|
|
return static_cpu_has(X86_FEATURE_SEP) &&
|
|
regs->cs == __USER_CS && regs->ss == __USER_DS &&
|
|
regs->ip == landing_pad &&
|
|
(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
|
|
#endif
|
|
}
|
|
#endif
|