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Merge branch 'x86-traps' (trap handling from Andy Lutomirski)

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Merge x86-64 iret fixes from Andy Lutomirski:
 "This addresses the following issues:

   - an unrecoverable double-fault triggerable with modify_ldt.
   - invalid stack usage in espfix64 failed IRET recovery from IST
     context.
   - invalid stack usage in non-espfix64 failed IRET recovery from IST
     context.

  It also makes a good but IMO scary change: non-espfix64 failed IRET
  will now report the correct error.  Hopefully nothing depended on the
  old incorrect behavior, but maybe Wine will get confused in some
  obscure corner case"

* emailed patches from Andy Lutomirski <luto@amacapital.net>:
  x86_64, traps: Rework bad_iret
  x86_64, traps: Stop using IST for #SS
  x86_64, traps: Fix the espfix64 #DF fixup and rewrite it in C
This commit is contained in:
Linus Torvalds 2014-11-23 13:56:55 -08:00
commit 00c89b2f11
6 changed files with 82 additions and 84 deletions
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1
arch/x86/include/asm/page_32_types.h
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@ -20,7 +20,6 @@
#define THREAD_SIZE_ORDER 1
#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
#define STACKFAULT_STACK 0
#define DOUBLEFAULT_STACK 1
#define NMI_STACK 0
#define DEBUG_STACK 0

11
arch/x86/include/asm/page_64_types.h
View File

@ -14,12 +14,11 @@
#define IRQ_STACK_ORDER 2
#define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER)
#define STACKFAULT_STACK 1
#define DOUBLEFAULT_STACK 2
#define NMI_STACK 3
#define DEBUG_STACK 4
#define MCE_STACK 5
#define N_EXCEPTION_STACKS 5 /* hw limit: 7 */
#define DOUBLEFAULT_STACK 1
#define NMI_STACK 2
#define DEBUG_STACK 3
#define MCE_STACK 4
#define N_EXCEPTION_STACKS 4 /* hw limit: 7 */
#define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT)
#define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1))

1
arch/x86/include/asm/traps.h
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@ -39,6 +39,7 @@ asmlinkage void simd_coprocessor_error(void);
#ifdef CONFIG_TRACING
asmlinkage void trace_page_fault(void);
#define trace_stack_segment stack_segment
#define trace_divide_error divide_error
#define trace_bounds bounds
#define trace_invalid_op invalid_op

1
arch/x86/kernel/dumpstack_64.c
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@ -24,7 +24,6 @@ static char x86_stack_ids[][8] = {
[ DEBUG_STACK-1 ] = "#DB",
[ NMI_STACK-1 ] = "NMI",
[ DOUBLEFAULT_STACK-1 ] = "#DF",
[ STACKFAULT_STACK-1 ] = "#SS",
[ MCE_STACK-1 ] = "#MC",
#if DEBUG_STKSZ > EXCEPTION_STKSZ
[ N_EXCEPTION_STACKS ...

81
arch/x86/kernel/entry_64.S
View File

@ -828,9 +828,15 @@ ENTRY(native_iret)
jnz native_irq_return_ldt
#endif
.global native_irq_return_iret
native_irq_return_iret:
/*
* This may fault. Non-paranoid faults on return to userspace are
* handled by fixup_bad_iret. These include #SS, #GP, and #NP.
* Double-faults due to espfix64 are handled in do_double_fault.
* Other faults here are fatal.
*/
iretq
_ASM_EXTABLE(native_irq_return_iret, bad_iret)
#ifdef CONFIG_X86_ESPFIX64
native_irq_return_ldt:
@ -858,25 +864,6 @@ native_irq_return_ldt:
jmp native_irq_return_iret
#endif
.section .fixup,"ax"
bad_iret:
/*
* The iret traps when the %cs or %ss being restored is bogus.
* We've lost the original trap vector and error code.
* #GPF is the most likely one to get for an invalid selector.
* So pretend we completed the iret and took the #GPF in user mode.
*
* We are now running with the kernel GS after exception recovery.
* But error_entry expects us to have user GS to match the user %cs,
* so swap back.
*/
pushq $0
SWAPGS
jmp general_protection
.previous
/* edi: workmask, edx: work */
retint_careful:
CFI_RESTORE_STATE
@ -922,37 +909,6 @@ ENTRY(retint_kernel)
CFI_ENDPROC
END(common_interrupt)
/*
* If IRET takes a fault on the espfix stack, then we
* end up promoting it to a doublefault. In that case,
* modify the stack to make it look like we just entered
* the #GP handler from user space, similar to bad_iret.
*/
#ifdef CONFIG_X86_ESPFIX64
ALIGN
__do_double_fault:
XCPT_FRAME 1 RDI+8
movq RSP(%rdi),%rax /* Trap on the espfix stack? */
sarq $PGDIR_SHIFT,%rax
cmpl $ESPFIX_PGD_ENTRY,%eax
jne do_double_fault /* No, just deliver the fault */
cmpl $__KERNEL_CS,CS(%rdi)
jne do_double_fault
movq RIP(%rdi),%rax
cmpq $native_irq_return_iret,%rax
jne do_double_fault /* This shouldn't happen... */
movq PER_CPU_VAR(kernel_stack),%rax
subq $(6*8-KERNEL_STACK_OFFSET),%rax /* Reset to original stack */
movq %rax,RSP(%rdi)
movq $0,(%rax) /* Missing (lost) #GP error code */
movq $general_protection,RIP(%rdi)
retq
CFI_ENDPROC
END(__do_double_fault)
#else
# define __do_double_fault do_double_fault
#endif
/*
* APIC interrupts.
*/
@ -1124,7 +1080,7 @@ idtentry overflow do_overflow has_error_code=0
idtentry bounds do_bounds has_error_code=0
idtentry invalid_op do_invalid_op has_error_code=0
idtentry device_not_available do_device_not_available has_error_code=0
idtentry double_fault __do_double_fault has_error_code=1 paranoid=1
idtentry double_fault do_double_fault has_error_code=1 paranoid=1
idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0
idtentry invalid_TSS do_invalid_TSS has_error_code=1
idtentry segment_not_present do_segment_not_present has_error_code=1
@ -1289,7 +1245,7 @@ apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
idtentry int3 do_int3 has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
idtentry stack_segment do_stack_segment has_error_code=1 paranoid=1
idtentry stack_segment do_stack_segment has_error_code=1
#ifdef CONFIG_XEN
idtentry xen_debug do_debug has_error_code=0
idtentry xen_int3 do_int3 has_error_code=0
@ -1399,17 +1355,16 @@ error_sti:
/*
* There are two places in the kernel that can potentially fault with
* usergs. Handle them here. The exception handlers after iret run with
* kernel gs again, so don't set the user space flag. B stepping K8s
* sometimes report an truncated RIP for IRET exceptions returning to
* compat mode. Check for these here too.
* usergs. Handle them here. B stepping K8s sometimes report a
* truncated RIP for IRET exceptions returning to compat mode. Check
* for these here too.
*/
error_kernelspace:
CFI_REL_OFFSET rcx, RCX+8
incl %ebx
leaq native_irq_return_iret(%rip),%rcx
cmpq %rcx,RIP+8(%rsp)
je error_swapgs
je error_bad_iret
movl %ecx,%eax /* zero extend */
cmpq %rax,RIP+8(%rsp)
je bstep_iret
@ -1420,7 +1375,15 @@ error_kernelspace:
bstep_iret:
/* Fix truncated RIP */
movq %rcx,RIP+8(%rsp)
jmp error_swapgs
/* fall through */
error_bad_iret:
SWAPGS
mov %rsp,%rdi
call fixup_bad_iret
mov %rax,%rsp
decl %ebx /* Return to usergs */
jmp error_sti
CFI_ENDPROC
END(error_entry)

71
arch/x86/kernel/traps.c
View File

@ -233,32 +233,40 @@ DO_ERROR(X86_TRAP_UD, SIGILL, "invalid opcode", invalid_op)
DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, "coprocessor segment overrun",coprocessor_segment_overrun)
DO_ERROR(X86_TRAP_TS, SIGSEGV, "invalid TSS", invalid_TSS)
DO_ERROR(X86_TRAP_NP, SIGBUS, "segment not present", segment_not_present)
#ifdef CONFIG_X86_32
DO_ERROR(X86_TRAP_SS, SIGBUS, "stack segment", stack_segment)
#endif
DO_ERROR(X86_TRAP_AC, SIGBUS, "alignment check", alignment_check)
#ifdef CONFIG_X86_64
/* Runs on IST stack */
dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code)
{
enum ctx_state prev_state;
prev_state = exception_enter();
if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
X86_TRAP_SS, SIGBUS) != NOTIFY_STOP) {
preempt_conditional_sti(regs);
do_trap(X86_TRAP_SS, SIGBUS, "stack segment", regs, error_code, NULL);
preempt_conditional_cli(regs);
}
exception_exit(prev_state);
}
dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
{
static const char str[] = "double fault";
struct task_struct *tsk = current;
#ifdef CONFIG_X86_ESPFIX64
extern unsigned char native_irq_return_iret[];
/*
* If IRET takes a non-IST fault on the espfix64 stack, then we
* end up promoting it to a doublefault. In that case, modify
* the stack to make it look like we just entered the #GP
* handler from user space, similar to bad_iret.
*/
if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
regs->cs == __KERNEL_CS &&
regs->ip == (unsigned long)native_irq_return_iret)
{
struct pt_regs *normal_regs = task_pt_regs(current);
/* Fake a #GP(0) from userspace. */
memmove(&normal_regs->ip, (void *)regs->sp, 5*8);
normal_regs->orig_ax = 0; /* Missing (lost) #GP error code */
regs->ip = (unsigned long)general_protection;
regs->sp = (unsigned long)&normal_regs->orig_ax;
return;
}
#endif
exception_enter();
/* Return not checked because double check cannot be ignored */
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
@ -399,6 +407,35 @@ asmlinkage __visible struct pt_regs *sync_regs(struct pt_regs *eregs)
return regs;
}
NOKPROBE_SYMBOL(sync_regs);
struct bad_iret_stack {
void *error_entry_ret;
struct pt_regs regs;
};
asmlinkage __visible
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.
*/
struct bad_iret_stack *new_stack =
container_of(task_pt_regs(current),
struct bad_iret_stack, regs);
/* Copy the IRET target to the new stack. */
memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
/* Copy the remainder of the stack from the current stack. */
memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
BUG_ON(!user_mode_vm(&new_stack->regs));
return new_stack;
}
#endif
/*
@ -778,7 +815,7 @@ void __init trap_init(void)
set_intr_gate(X86_TRAP_OLD_MF, coprocessor_segment_overrun);
set_intr_gate(X86_TRAP_TS, invalid_TSS);
set_intr_gate(X86_TRAP_NP, segment_not_present);
set_intr_gate_ist(X86_TRAP_SS, &stack_segment, STACKFAULT_STACK);
set_intr_gate(X86_TRAP_SS, stack_segment);
set_intr_gate(X86_TRAP_GP, general_protection);
set_intr_gate(X86_TRAP_SPURIOUS, spurious_interrupt_bug);
set_intr_gate(X86_TRAP_MF, coprocessor_error);