diff options
Diffstat (limited to 'arch/x86/entry/entry_32.S')
| -rw-r--r-- | arch/x86/entry/entry_32.S | 42 |
1 files changed, 30 insertions, 12 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 76109068149f..b2e1d446bdf8 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -287,7 +287,26 @@ 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 $5*4, %esp /* remove xen-provided frame */ + jmp sysenter_past_esp +#endif + ENTRY(entry_SYSENTER_32) movl TSS_sysenter_sp0(%esp), %esp sysenter_past_esp: @@ -301,19 +320,25 @@ sysenter_past_esp: SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest */ /* - * SYSENTER doesn't filter flags, so we need to clear NT and AC - * ourselves. To save a few cycles, we can check whether + * 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, PT_EFLAGS(%esp) + testl $X86_EFLAGS_NT|X86_EFLAGS_AC|X86_EFLAGS_TF, PT_EFLAGS(%esp) jnz .Lsysenter_fix_flags .Lsysenter_flags_fixed: @@ -369,6 +394,7 @@ sysenter_past_esp: pushl $X86_EFLAGS_FIXED popfl jmp .Lsysenter_flags_fixed +GLOBAL(__end_SYSENTER_singlestep_region) ENDPROC(entry_SYSENTER_32) # system call handler stub @@ -651,14 +677,6 @@ 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 |