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Commit 425be567 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
Browse files

x86/asm/irq: Stop relying on magic JMP behavior for early_idt_handlers 



The early_idt_handlers asm code generates an array of entry
points spaced nine bytes apart.  It's not really clear from that
code or from the places that reference it what's going on, and
the code only works in the first place because GAS never
generates two-byte JMP instructions when jumping to global
labels.

Clean up the code to generate the correct array stride (member size)
explicitly. This should be considerably more robust against
screw-ups, as GAS will warn if a .fill directive has a negative
count.  Using '. =' to advance would have been even more robust
(it would generate an actual error if it tried to move
backwards), but it would pad with nulls, confusing anyone who
tries to disassemble the code.  The new scheme should be much
clearer to future readers.

While we're at it, improve the comments and rename the array and
common code.

Binutils may start relaxing jumps to non-weak labels.  If so,
this change will fix our build, and we may need to backport this
change.

Before, on x86_64:

  0000000000000000 <early_idt_handlers>:
     0:   6a 00                   pushq  $0x0
     2:   6a 00                   pushq  $0x0
     4:   e9 00 00 00 00          jmpq   9 <early_idt_handlers+0x9>
                          5: R_X86_64_PC32        early_idt_handler-0x4
  ...
    48:   66 90                   xchg   %ax,%ax
    4a:   6a 08                   pushq  $0x8
    4c:   e9 00 00 00 00          jmpq   51 <early_idt_handlers+0x51>
                          4d: R_X86_64_PC32       early_idt_handler-0x4
  ...
   117:   6a 00                   pushq  $0x0
   119:   6a 1f                   pushq  $0x1f
   11b:   e9 00 00 00 00          jmpq   120 <early_idt_handler>
                          11c: R_X86_64_PC32      early_idt_handler-0x4

After:

  0000000000000000 <early_idt_handler_array>:
     0:   6a 00                   pushq  $0x0
     2:   6a 00                   pushq  $0x0
     4:   e9 14 01 00 00          jmpq   11d <early_idt_handler_common>
  ...
    48:   6a 08                   pushq  $0x8
    4a:   e9 d1 00 00 00          jmpq   120 <early_idt_handler_common>
    4f:   cc                      int3
    50:   cc                      int3
  ...
   117:   6a 00                   pushq  $0x0
   119:   6a 1f                   pushq  $0x1f
   11b:   eb 03                   jmp    120 <early_idt_handler_common>
   11d:   cc                      int3
   11e:   cc                      int3
   11f:   cc                      int3

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Acked-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Cc: Binutils <binutils@sourceware.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H.J. Lu <hjl.tools@gmail.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/ac027962af343b0c599cbfcf50b945ad2ef3d7a8.1432336324.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c2affbf9

arch/x86/include/asm/segment.h

+12 −2
Original line number Diff line number Diff line
@@ -231,11 +231,21 @@ 
#define TLS_SIZE			(GDT_ENTRY_TLS_ENTRIES* 8)



#ifdef __KERNEL__



/*

 * early_idt_handler_array is an array of entry points referenced in the

 * early IDT.  For simplicity, it's a real array with one entry point

 * every nine bytes.  That leaves room for an optional 'push $0' if the

 * vector has no error code (two bytes), a 'push $vector_number' (two

 * bytes), and a jump to the common entry code (up to five bytes).

 */

#define EARLY_IDT_HANDLER_SIZE 9



#ifndef __ASSEMBLY__



extern const char early_idt_handlers[NUM_EXCEPTION_VECTORS][2+2+5];

extern const char early_idt_handler_array[NUM_EXCEPTION_VECTORS][EARLY_IDT_HANDLER_SIZE];

#ifdef CONFIG_TRACING

# define trace_early_idt_handlers early_idt_handlers

# define trace_early_idt_handler_array early_idt_handler_array

#endif



/*

arch/x86/kernel/head64.c

+1 −1
Original line number Diff line number Diff line
@@ -167,7 +167,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data) 
	clear_bss();



	for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)

		set_intr_gate(i, early_idt_handlers[i]);

		set_intr_gate(i, early_idt_handler_array[i]);

	load_idt((const struct desc_ptr *)&idt_descr);



	copy_bootdata(__va(real_mode_data));

arch/x86/kernel/head_32.S

+18 −15
Original line number Diff line number Diff line
@@ -478,21 +478,22 @@ is486: 
__INIT

setup_once:

	/*

	 * Set up a idt with 256 entries pointing to ignore_int,

	 * interrupt gates. It doesn't actually load idt - that needs

	 * to be done on each CPU. Interrupts are enabled elsewhere,

	 * when we can be relatively sure everything is ok.

	 * Set up a idt with 256 interrupt gates that push zero if there

	 * is no error code and then jump to early_idt_handler_common.

	 * It doesn't actually load the idt - that needs to be done on

	 * each CPU. Interrupts are enabled elsewhere, when we can be

	 * relatively sure everything is ok.

	 */



	movl $idt_table,%edi

	movl $early_idt_handlers,%eax

	movl $early_idt_handler_array,%eax

	movl $NUM_EXCEPTION_VECTORS,%ecx

1:

	movl %eax,(%edi)

	movl %eax,4(%edi)

	/* interrupt gate, dpl=0, present */

	movl $(0x8E000000 + __KERNEL_CS),2(%edi)

	addl $9,%eax

	addl $EARLY_IDT_HANDLER_SIZE,%eax

	addl $8,%edi

	loop 1b
@@ -524,26 +525,28 @@ setup_once: 
	andl $0,setup_once_ref	/* Once is enough, thanks */

	ret



ENTRY(early_idt_handlers)

ENTRY(early_idt_handler_array)

	# 36(%esp) %eflags

	# 32(%esp) %cs

	# 28(%esp) %eip

	# 24(%rsp) error code

	i = 0

	.rept NUM_EXCEPTION_VECTORS

	.if (EXCEPTION_ERRCODE_MASK >> i) & 1

	ASM_NOP2

	.else

	.ifeq (EXCEPTION_ERRCODE_MASK >> i) & 1

	pushl $0		# Dummy error code, to make stack frame uniform

	.endif

	pushl $i		# 20(%esp) Vector number

	jmp early_idt_handler

	jmp early_idt_handler_common

	i = i + 1

	.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc

	.endr

ENDPROC(early_idt_handlers)

ENDPROC(early_idt_handler_array)

	

	/* This is global to keep gas from relaxing the jumps */

ENTRY(early_idt_handler)

early_idt_handler_common:

	/*

	 * The stack is the hardware frame, an error code or zero, and the

	 * vector number.

	 */

	cld



	cmpl $2,(%esp)		# X86_TRAP_NMI
@@ -603,7 +606,7 @@ ex_entry: 
is_nmi:

	addl $8,%esp		/* drop vector number and error code */

	iret

ENDPROC(early_idt_handler)

ENDPROC(early_idt_handler_common)



/* This is the default interrupt "handler" :-) */

	ALIGN

arch/x86/kernel/head_64.S

+11 −9
Original line number Diff line number Diff line
@@ -321,26 +321,28 @@ bad_address: 
	jmp bad_address



	__INIT

	.globl early_idt_handlers

early_idt_handlers:

ENTRY(early_idt_handler_array)

	# 104(%rsp) %rflags

	#  96(%rsp) %cs

	#  88(%rsp) %rip

	#  80(%rsp) error code

	i = 0

	.rept NUM_EXCEPTION_VECTORS

	.if (EXCEPTION_ERRCODE_MASK >> i) & 1

	ASM_NOP2

	.else

	.ifeq (EXCEPTION_ERRCODE_MASK >> i) & 1

	pushq $0		# Dummy error code, to make stack frame uniform

	.endif

	pushq $i		# 72(%rsp) Vector number

	jmp early_idt_handler

	jmp early_idt_handler_common

	i = i + 1

	.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc

	.endr

ENDPROC(early_idt_handler_array)



/* This is global to keep gas from relaxing the jumps */

ENTRY(early_idt_handler)

early_idt_handler_common:

	/*

	 * The stack is the hardware frame, an error code or zero, and the

	 * vector number.

	 */

	cld



	cmpl $2,(%rsp)		# X86_TRAP_NMI
@@ -412,7 +414,7 @@ ENTRY(early_idt_handler) 
is_nmi:

	addq $16,%rsp		# drop vector number and error code

	INTERRUPT_RETURN

ENDPROC(early_idt_handler)

ENDPROC(early_idt_handler_common)



	__INITDATA