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x86/entry/64: Use a per-CPU trampoline stack for IDT entries

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Historically, IDT entries from usermode have always gone directly
to the running task's kernel stack.  Rearrange it so that we enter on
a per-CPU trampoline stack and then manually switch to the task's stack.
This touches a couple of extra cachelines, but it gives us a chance
to run some code before we touch the kernel stack.

The asm isn't exactly beautiful, but I think that fully refactoring
it can wait.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150606.225330557@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-12-04 15:07:23 +01:00 committed by Ingo Molnar
parent 6d9256f0a8
commit 7f2590a110
6 changed files with 72 additions and 32 deletions
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67
arch/x86/entry/entry_64.S
View File

@ -560,6 +560,13 @@ END(irq_entries_start)
/* 0(%rsp): ~(interrupt number) */
.macro interrupt func
cld
testb $3, CS-ORIG_RAX(%rsp)
jz 1f
SWAPGS
call switch_to_thread_stack
1:
ALLOC_PT_GPREGS_ON_STACK
SAVE_C_REGS
SAVE_EXTRA_REGS
@ -569,12 +576,8 @@ END(irq_entries_start)
jz 1f
/*
* IRQ from user mode. Switch to kernel gsbase and inform context
* tracking that we're in kernel mode.
*/
SWAPGS
/*
* IRQ from user mode.
*
* We need to tell lockdep that IRQs are off. We can't do this until
* we fix gsbase, and we should do it before enter_from_user_mode
* (which can take locks). Since TRACE_IRQS_OFF idempotent,
@ -828,6 +831,32 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
*/
#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss) + (TSS_ist + ((x) - 1) * 8)
/*
* Switch to the thread stack. This is called with the IRET frame and
* orig_ax on the stack. (That is, RDI..R12 are not on the stack and
* space has not been allocated for them.)
*/
ENTRY(switch_to_thread_stack)
UNWIND_HINT_FUNC
pushq %rdi
movq %rsp, %rdi
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI
pushq 7*8(%rdi) /* regs->ss */
pushq 6*8(%rdi) /* regs->rsp */
pushq 5*8(%rdi) /* regs->eflags */
pushq 4*8(%rdi) /* regs->cs */
pushq 3*8(%rdi) /* regs->ip */
pushq 2*8(%rdi) /* regs->orig_ax */
pushq 8(%rdi) /* return address */
UNWIND_HINT_FUNC
movq (%rdi), %rdi
ret
END(switch_to_thread_stack)
.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
ENTRY(\sym)
UNWIND_HINT_IRET_REGS offset=\has_error_code*8
@ -845,11 +874,12 @@ ENTRY(\sym)
ALLOC_PT_GPREGS_ON_STACK
.if \paranoid
.if \paranoid == 1
.if \paranoid < 2
testb $3, CS(%rsp) /* If coming from userspace, switch stacks */
jnz 1f
jnz .Lfrom_usermode_switch_stack_\@
.endif
.if \paranoid
call paranoid_entry
.else
call error_entry
@ -891,20 +921,15 @@ ENTRY(\sym)
jmp error_exit
.endif
.if \paranoid == 1
.if \paranoid < 2
/*
* Paranoid entry from userspace. Switch stacks and treat it
* Entry from userspace. Switch stacks and treat it
* as a normal entry. This means that paranoid handlers
* run in real process context if user_mode(regs).
*/
1:
.Lfrom_usermode_switch_stack_\@:
call error_entry
movq %rsp, %rdi /* pt_regs pointer */
call sync_regs
movq %rax, %rsp /* switch stack */
movq %rsp, %rdi /* pt_regs pointer */
.if \has_error_code
@ -1165,6 +1190,14 @@ ENTRY(error_entry)
SWAPGS
.Lerror_entry_from_usermode_after_swapgs:
/* Put us onto the real thread stack. */
popq %r12 /* save return addr in %12 */
movq %rsp, %rdi /* arg0 = pt_regs pointer */
call sync_regs
movq %rax, %rsp /* switch stack */
ENCODE_FRAME_POINTER
pushq %r12
/*
* We need to tell lockdep that IRQs are off. We can't do this until
* we fix gsbase, and we should do it before enter_from_user_mode

5
arch/x86/entry/entry_64_compat.S
View File

@ -306,8 +306,11 @@ ENTRY(entry_INT80_compat)
*/
movl %eax, %eax
/* Construct struct pt_regs on stack (iret frame is already on stack) */
pushq %rax /* pt_regs->orig_ax */
/* switch to thread stack expects orig_ax to be pushed */
call switch_to_thread_stack
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */

4
arch/x86/include/asm/switch_to.h
View File

@ -90,10 +90,12 @@ static inline void refresh_sysenter_cs(struct thread_struct *thread)
/* This is used when switching tasks or entering/exiting vm86 mode. */
static inline void update_sp0(struct task_struct *task)
{
/* On x86_64, sp0 always points to the entry trampoline stack, which is constant: */
#ifdef CONFIG_X86_32
load_sp0(task->thread.sp0);
#else
load_sp0(task_top_of_stack(task));
if (static_cpu_has(X86_FEATURE_XENPV))
load_sp0(task_top_of_stack(task));
#endif
}

1
arch/x86/include/asm/traps.h
View File

@ -75,7 +75,6 @@ dotraplinkage void do_segment_not_present(struct pt_regs *, long);
dotraplinkage void do_stack_segment(struct pt_regs *, long);
#ifdef CONFIG_X86_64
dotraplinkage void do_double_fault(struct pt_regs *, long);
asmlinkage struct pt_regs *sync_regs(struct pt_regs *);
#endif
dotraplinkage void do_general_protection(struct pt_regs *, long);
dotraplinkage void do_page_fault(struct pt_regs *, unsigned long);

6
arch/x86/kernel/cpu/common.c
View File

@ -1623,11 +1623,13 @@ void cpu_init(void)
setup_cpu_entry_area(cpu);
/*
* Initialize the TSS. Don't bother initializing sp0, as the initial
* task never enters user mode.
* Initialize the TSS. sp0 points to the entry trampoline stack
* regardless of what task is running.
*/
set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
load_TR_desc();
load_sp0((unsigned long)&get_cpu_entry_area(cpu)->tss +
offsetofend(struct tss_struct, SYSENTER_stack));
load_mm_ldt(&init_mm);

21
arch/x86/kernel/traps.c
View File

@ -619,14 +619,15 @@ NOKPROBE_SYMBOL(do_int3);
#ifdef CONFIG_X86_64
/*
* Help handler running on IST stack to switch off the IST stack if the
* interrupted code was in user mode. The actual stack switch is done in
* entry_64.S
* Help handler running on a per-cpu (IST or entry trampoline) stack
* to switch to the normal thread stack if the interrupted code was in
* user mode. The actual stack switch is done in entry_64.S
*/
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
{
struct pt_regs *regs = task_pt_regs(current);
*regs = *eregs;
struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
if (regs != eregs)
*regs = *eregs;
return regs;
}
NOKPROBE_SYMBOL(sync_regs);
@ -642,13 +643,13 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
/*
* This is called from entry_64.S early in handling a fault
* caused by a bad iret to user mode. To handle the fault
* correctly, we want move our stack frame to task_pt_regs
* and we want to pretend that the exception came from the
* iret target.
* correctly, we want to move our stack frame to where it would
* be had we entered directly on the entry stack (rather than
* just below the IRET frame) and we want to pretend that the
* exception came from the IRET target.
*/
struct bad_iret_stack *new_stack =
container_of(task_pt_regs(current),
struct bad_iret_stack, regs);
(struct bad_iret_stack *)this_cpu_read(cpu_tss.x86_tss.sp0) - 1;
/* Copy the IRET target to the new stack. */
memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);