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x86_64, traps: Fix the espfix64 #DF fixup and rewrite it in C

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There's nothing special enough about the espfix64 double fault fixup to
justify writing it in assembly.  Move it to C.

This also fixes a bug: if the double fault came from an IST stack, the
old asm code would return to a partially uninitialized stack frame.

Fixes: 3891a04aaf
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andy Lutomirski 2014-11-22 18:00:31 -08:00 committed by Linus Torvalds
parent fc14f9c127
commit af726f21ed
2 changed files with 26 additions and 32 deletions
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34
arch/x86/kernel/entry_64.S
View File

@ -828,6 +828,7 @@ ENTRY(native_iret)
jnz native_irq_return_ldt
#endif
.global native_irq_return_iret
native_irq_return_iret:
iretq
_ASM_EXTABLE(native_irq_return_iret, bad_iret)
@ -922,37 +923,6 @@ 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 +1094,7 @@ 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

24
arch/x86/kernel/traps.c
View File

@ -259,6 +259,30 @@ 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);