diff options
Diffstat (limited to 'arch/x86/entry/entry_32.S')
| -rw-r--r-- | arch/x86/entry/entry_32.S | 268 |
1 files changed, 176 insertions, 92 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index bb3e376d0..10868aa73 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -40,7 +40,7 @@ #include <asm/processor-flags.h> #include <asm/ftrace.h> #include <asm/irq_vectors.h> -#include <asm/cpufeature.h> +#include <asm/cpufeatures.h> #include <asm/alternative-asm.h> #include <asm/asm.h> #include <asm/smap.h> @@ -287,14 +287,64 @@ need_resched: END(resume_kernel) #endif - # SYSENTER call handler stub +GLOBAL(__begin_SYSENTER_singlestep_region) +/* + * All code from here through __end_SYSENTER_singlestep_region is subject + * to being single-stepped if a user program sets TF and executes SYSENTER. + * There is absolutely nothing that we can do to prevent this from happening + * (thanks Intel!). To keep our handling of this situation as simple as + * possible, we handle TF just like AC and NT, except that our #DB handler + * will ignore all of the single-step traps generated in this range. + */ + +#ifdef CONFIG_XEN +/* + * Xen doesn't set %esp to be precisely what the normal SYSENTER + * entry point expects, so fix it up before using the normal path. + */ +ENTRY(xen_sysenter_target) + addl $5*4, %esp /* remove xen-provided frame */ + jmp sysenter_past_esp +#endif + +/* + * 32-bit SYSENTER entry. + * + * 32-bit system calls through the vDSO's __kernel_vsyscall enter here + * if X86_FEATURE_SEP is available. This is the preferred system call + * entry on 32-bit systems. + * + * 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, ESP, CS, and EIP 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 EIP (!!!), ESP, or EFLAGS. + * + * To avoid losing track of EFLAGS.VM (and thus potentially corrupting + * user and/or vm86 state), we explicitly disable the SYSENTER + * instruction in vm86 mode by reprogramming the MSRs. + * + * Arguments: + * eax system call number + * ebx arg1 + * ecx arg2 + * edx arg3 + * esi arg4 + * edi arg5 + * ebp user stack + * 0(%ebp) arg6 + */ ENTRY(entry_SYSENTER_32) movl TSS_sysenter_sp0(%esp), %esp sysenter_past_esp: pushl $__USER_DS /* pt_regs->ss */ pushl %ebp /* pt_regs->sp (stashed in bp) */ pushfl /* pt_regs->flags (except IF = 0) */ - ASM_CLAC /* Clear AC after saving FLAGS */ orl $X86_EFLAGS_IF, (%esp) /* Fix IF */ pushl $__USER_CS /* pt_regs->cs */ pushl $0 /* pt_regs->ip = 0 (placeholder) */ @@ -302,6 +352,29 @@ sysenter_past_esp: SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */ /* + * SYSENTER doesn't filter flags, so we need to clear NT, AC + * and TF 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, PT_EFLAGS(%esp) + jnz .Lsysenter_fix_flags +.Lsysenter_flags_fixed: + + /* * User mode is traced as though IRQs are on, and SYSENTER * turned them off. */ @@ -327,6 +400,15 @@ sysenter_past_esp: popl %eax /* pt_regs->ax */ /* + * Restore all flags except IF. (We restore IF separately because + * STI gives a one-instruction window in which we won't be interrupted, + * whereas POPF does not.) + */ + addl $PT_EFLAGS-PT_DS, %esp /* point esp at pt_regs->flags */ + btr $X86_EFLAGS_IF_BIT, (%esp) + popfl + + /* * Return back to the vDSO, which will pop ecx and edx. * Don't bother with DS and ES (they already contain __USER_DS). */ @@ -339,28 +421,63 @@ sysenter_past_esp: .popsection _ASM_EXTABLE(1b, 2b) PTGS_TO_GS_EX + +.Lsysenter_fix_flags: + pushl $X86_EFLAGS_FIXED + popfl + jmp .Lsysenter_flags_fixed +GLOBAL(__end_SYSENTER_singlestep_region) ENDPROC(entry_SYSENTER_32) - # system call handler stub +/* + * 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 any 32-bit perform 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. (64-bit programs can use INT $0x80 as well, but they can + * only run on 64-bit kernels and therefore land in + * entry_INT80_compat.) + * + * This is considered a slow path. It is not used by most libc + * implementations on modern hardware except during process startup. + * + * Arguments: + * eax system call number + * ebx arg1 + * ecx arg2 + * edx arg3 + * esi arg4 + * edi arg5 + * ebp arg6 + */ ENTRY(entry_INT80_32) ASM_CLAC pushl %eax /* pt_regs->orig_ax */ SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */ /* - * User mode is traced as though IRQs are on. Unlike the 64-bit - * case, INT80 is a trap gate on 32-bit kernels, so interrupts - * are already on (unless user code is messing around with iopl). + * User mode is traced as though IRQs are on, and the interrupt gate + * turned them off. */ + TRACE_IRQS_OFF movl %esp, %eax - call do_syscall_32_irqs_on + call do_int80_syscall_32 .Lsyscall_32_done: restore_all: TRACE_IRQS_IRET restore_all_notrace: #ifdef CONFIG_X86_ESPFIX32 + ALTERNATIVE "jmp restore_nocheck", "", X86_BUG_ESPFIX + movl PT_EFLAGS(%esp), %eax # mix EFLAGS, SS and CS /* * Warning: PT_OLDSS(%esp) contains the wrong/random values if we @@ -387,19 +504,6 @@ ENTRY(iret_exc ) #ifdef CONFIG_X86_ESPFIX32 ldt_ss: -#ifdef CONFIG_PARAVIRT - /* - * The kernel can't run on a non-flat stack if paravirt mode - * is active. Rather than try to fixup the high bits of - * ESP, bypass this code entirely. This may break DOSemu - * and/or Wine support in a paravirt VM, although the option - * is still available to implement the setting of the high - * 16-bits in the INTERRUPT_RETURN paravirt-op. - */ - cmpl $0, pv_info+PARAVIRT_enabled - jne restore_nocheck -#endif - /* * Setup and switch to ESPFIX stack * @@ -632,14 +736,6 @@ ENTRY(spurious_interrupt_bug) END(spurious_interrupt_bug) #ifdef CONFIG_XEN -/* - * Xen doesn't set %esp to be precisely what the normal SYSENTER - * entry point expects, so fix it up before using the normal path. - */ -ENTRY(xen_sysenter_target) - addl $5*4, %esp /* remove xen-provided frame */ - jmp sysenter_past_esp - ENTRY(xen_hypervisor_callback) pushl $-1 /* orig_ax = -1 => not a system call */ SAVE_ALL @@ -939,51 +1035,48 @@ error_code: jmp ret_from_exception END(page_fault) -/* - * Debug traps and NMI can happen at the one SYSENTER instruction - * that sets up the real kernel stack. Check here, since we can't - * allow the wrong stack to be used. - * - * "TSS_sysenter_sp0+12" is because the NMI/debug handler will have - * already pushed 3 words if it hits on the sysenter instruction: - * eflags, cs and eip. - * - * We just load the right stack, and push the three (known) values - * by hand onto the new stack - while updating the return eip past - * the instruction that would have done it for sysenter. - */ -.macro FIX_STACK offset ok label - cmpw $__KERNEL_CS, 4(%esp) - jne \ok -\label: - movl TSS_sysenter_sp0 + \offset(%esp), %esp - pushfl - pushl $__KERNEL_CS - pushl $sysenter_past_esp -.endm - ENTRY(debug) + /* + * #DB can happen at the first instruction of + * entry_SYSENTER_32 or in Xen's SYSENTER prologue. If this + * happens, then we will be running on a very small stack. We + * need to detect this condition and switch to the thread + * stack before calling any C code at all. + * + * If you edit this code, keep in mind that NMIs can happen in here. + */ ASM_CLAC - cmpl $entry_SYSENTER_32, (%esp) - jne debug_stack_correct - FIX_STACK 12, debug_stack_correct, debug_esp_fix_insn -debug_stack_correct: pushl $-1 # mark this as an int SAVE_ALL - TRACE_IRQS_OFF xorl %edx, %edx # error code 0 movl %esp, %eax # pt_regs pointer + + /* Are we currently on the SYSENTER stack? */ + PER_CPU(cpu_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx) + subl %eax, %ecx /* ecx = (end of SYSENTER_stack) - esp */ + cmpl $SIZEOF_SYSENTER_stack, %ecx + jb .Ldebug_from_sysenter_stack + + TRACE_IRQS_OFF + call do_debug + jmp ret_from_exception + +.Ldebug_from_sysenter_stack: + /* We're on the SYSENTER stack. Switch off. */ + movl %esp, %ebp + movl PER_CPU_VAR(cpu_current_top_of_stack), %esp + TRACE_IRQS_OFF call do_debug + movl %ebp, %esp jmp ret_from_exception END(debug) /* - * NMI is doubly nasty. It can happen _while_ we're handling - * a debug fault, and the debug fault hasn't yet been able to - * clear up the stack. So we first check whether we got an - * NMI on the sysenter entry path, but after that we need to - * check whether we got an NMI on the debug path where the debug - * fault happened on the sysenter path. + * NMI is doubly nasty. It can happen on the first instruction of + * entry_SYSENTER_32 (just like #DB), but it can also interrupt the beginning + * of the #DB handler even if that #DB in turn hit before entry_SYSENTER_32 + * switched stacks. We handle both conditions by simply checking whether we + * interrupted kernel code running on the SYSENTER stack. */ ENTRY(nmi) ASM_CLAC @@ -994,41 +1087,32 @@ ENTRY(nmi) popl %eax je nmi_espfix_stack #endif - cmpl $entry_SYSENTER_32, (%esp) - je nmi_stack_fixup - pushl %eax - movl %esp, %eax - /* - * Do not access memory above the end of our stack page, - * it might not exist. - */ - andl $(THREAD_SIZE-1), %eax - cmpl $(THREAD_SIZE-20), %eax - popl %eax - jae nmi_stack_correct - cmpl $entry_SYSENTER_32, 12(%esp) - je nmi_debug_stack_check -nmi_stack_correct: - pushl %eax + + pushl %eax # pt_regs->orig_ax SAVE_ALL xorl %edx, %edx # zero error code movl %esp, %eax # pt_regs pointer + + /* Are we currently on the SYSENTER stack? */ + PER_CPU(cpu_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx) + subl %eax, %ecx /* ecx = (end of SYSENTER_stack) - esp */ + cmpl $SIZEOF_SYSENTER_stack, %ecx + jb .Lnmi_from_sysenter_stack + + /* Not on SYSENTER stack. */ call do_nmi jmp restore_all_notrace -nmi_stack_fixup: - FIX_STACK 12, nmi_stack_correct, 1 - jmp nmi_stack_correct - -nmi_debug_stack_check: - cmpw $__KERNEL_CS, 16(%esp) - jne nmi_stack_correct - cmpl $debug, (%esp) - jb nmi_stack_correct - cmpl $debug_esp_fix_insn, (%esp) - ja nmi_stack_correct - FIX_STACK 24, nmi_stack_correct, 1 - jmp nmi_stack_correct +.Lnmi_from_sysenter_stack: + /* + * We're on the SYSENTER stack. Switch off. No one (not even debug) + * is using the thread stack right now, so it's safe for us to use it. + */ + movl %esp, %ebp + movl PER_CPU_VAR(cpu_current_top_of_stack), %esp + call do_nmi + movl %ebp, %esp + jmp restore_all_notrace #ifdef CONFIG_X86_ESPFIX32 nmi_espfix_stack: |