diff options
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 106 | ||||
| -rw-r--r-- | arch/x86/kernel/traps.c | 25 |
2 files changed, 77 insertions, 54 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 501212f14c87..db13655c3a2a 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -361,15 +361,12 @@ system_call_fastpath: * Has incomplete stack frame and undefined top of stack. */ ret_from_sys_call: - movl $_TIF_ALLWORK_MASK,%edi - /* edi: flagmask */ -sysret_check: + testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) + jnz int_ret_from_sys_call_fixup /* Go the the slow path */ + LOCKDEP_SYS_EXIT DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF - movl TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET),%edx - andl %edi,%edx - jnz sysret_careful CFI_REMEMBER_STATE /* * sysretq will re-enable interrupts: @@ -383,49 +380,10 @@ sysret_check: USERGS_SYSRET64 CFI_RESTORE_STATE - /* Handle reschedules */ - /* edx: work, edi: workmask */ -sysret_careful: - bt $TIF_NEED_RESCHED,%edx - jnc sysret_signal - TRACE_IRQS_ON - ENABLE_INTERRUPTS(CLBR_NONE) - pushq_cfi %rdi - SCHEDULE_USER - popq_cfi %rdi - jmp sysret_check - /* Handle a signal */ -sysret_signal: - TRACE_IRQS_ON - ENABLE_INTERRUPTS(CLBR_NONE) -#ifdef CONFIG_AUDITSYSCALL - bt $TIF_SYSCALL_AUDIT,%edx - jc sysret_audit -#endif - /* - * We have a signal, or exit tracing or single-step. - * These all wind up with the iret return path anyway, - * so just join that path right now. - */ +int_ret_from_sys_call_fixup: FIXUP_TOP_OF_STACK %r11, -ARGOFFSET - jmp int_check_syscall_exit_work - -#ifdef CONFIG_AUDITSYSCALL - /* - * Return fast path for syscall audit. Call __audit_syscall_exit() - * directly and then jump back to the fast path with TIF_SYSCALL_AUDIT - * masked off. - */ -sysret_audit: - movq RAX-ARGOFFSET(%rsp),%rsi /* second arg, syscall return value */ - cmpq $-MAX_ERRNO,%rsi /* is it < -MAX_ERRNO? */ - setbe %al /* 1 if so, 0 if not */ - movzbl %al,%edi /* zero-extend that into %edi */ - call __audit_syscall_exit - movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi - jmp sysret_check -#endif /* CONFIG_AUDITSYSCALL */ + jmp int_ret_from_sys_call /* Do syscall tracing */ tracesys: @@ -794,6 +752,60 @@ retint_swapgs: /* return to user-space */ */ DISABLE_INTERRUPTS(CLBR_ANY) TRACE_IRQS_IRETQ + + /* + * Try to use SYSRET instead of IRET if we're returning to + * a completely clean 64-bit userspace context. + */ + movq (RCX-R11)(%rsp), %rcx + cmpq %rcx,(RIP-R11)(%rsp) /* RCX == RIP */ + jne opportunistic_sysret_failed + + /* + * On Intel CPUs, sysret with non-canonical RCX/RIP will #GP + * in kernel space. This essentially lets the user take over + * the kernel, since userspace controls RSP. It's not worth + * testing for canonicalness exactly -- this check detects any + * of the 17 high bits set, which is true for non-canonical + * or kernel addresses. (This will pessimize vsyscall=native. + * Big deal.) + * + * If virtual addresses ever become wider, this will need + * to be updated to remain correct on both old and new CPUs. + */ + .ifne __VIRTUAL_MASK_SHIFT - 47 + .error "virtual address width changed -- sysret checks need update" + .endif + shr $__VIRTUAL_MASK_SHIFT, %rcx + jnz opportunistic_sysret_failed + + cmpq $__USER_CS,(CS-R11)(%rsp) /* CS must match SYSRET */ + jne opportunistic_sysret_failed + + movq (R11-ARGOFFSET)(%rsp), %r11 + cmpq %r11,(EFLAGS-ARGOFFSET)(%rsp) /* R11 == RFLAGS */ + jne opportunistic_sysret_failed + + testq $X86_EFLAGS_RF,%r11 /* sysret can't restore RF */ + jnz opportunistic_sysret_failed + + /* nothing to check for RSP */ + + cmpq $__USER_DS,(SS-ARGOFFSET)(%rsp) /* SS must match SYSRET */ + jne opportunistic_sysret_failed + + /* + * We win! This label is here just for ease of understanding + * perf profiles. Nothing jumps here. + */ +irq_return_via_sysret: + CFI_REMEMBER_STATE + RESTORE_ARGS 1,8,1 + movq (RSP-RIP)(%rsp),%rsp + USERGS_SYSRET64 + CFI_RESTORE_STATE + +opportunistic_sysret_failed: SWAPGS jmp restore_args diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 7176f84f95a4..c74f2f5652da 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -110,15 +110,11 @@ static inline void preempt_conditional_cli(struct pt_regs *regs) enum ctx_state ist_enter(struct pt_regs *regs) { - /* - * We are atomic because we're on the IST stack (or we're on x86_32, - * in which case we still shouldn't schedule. - */ - preempt_count_add(HARDIRQ_OFFSET); + enum ctx_state prev_state; if (user_mode_vm(regs)) { /* Other than that, we're just an exception. */ - return exception_enter(); + prev_state = exception_enter(); } else { /* * We might have interrupted pretty much anything. In @@ -127,12 +123,27 @@ enum ctx_state ist_enter(struct pt_regs *regs) * but we need to notify RCU. */ rcu_nmi_enter(); - return IN_KERNEL; /* the value is irrelevant. */ + prev_state = IN_KERNEL; /* the value is irrelevant. */ } + + /* + * We are atomic because we're on the IST stack (or we're on x86_32, + * in which case we still shouldn't schedule). + * + * This must be after exception_enter(), because exception_enter() + * won't do anything if in_interrupt() returns true. + */ + preempt_count_add(HARDIRQ_OFFSET); + + /* This code is a bit fragile. Test it. */ + rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work"); + + return prev_state; } void ist_exit(struct pt_regs *regs, enum ctx_state prev_state) { + /* Must be before exception_exit. */ preempt_count_sub(HARDIRQ_OFFSET); if (user_mode_vm(regs)) |
