Commit 968ff9ee authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86, realmode: Remove indirect jumps in trampoline_32 and wakeup_asm



Remove indirect jumps in trampoline_32.S and the 32-bit part of
wakeup_asm.S.  There exist systems which are known to do weird
things if an SMI comes in right after a mode switch, and the
safest way to deal with it is to always follow with a simple
absolute far jump.  In the 64-bit code we then to a register
indirect near jump; follow that pattern for the 32-bit code.

Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-14-git-send-email-jarkko.sakkinen@intel.com
parent 056a43a6
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+13 −9
Original line number Diff line number Diff line
@@ -47,24 +47,29 @@ trampoline_data:

	cli			# We should be safe anyway

	movl	startup_32_smp, %eax	# where we need to go

	movl	$0xA5A5A5A5, trampoline_status
				# write marker for master knows we're running

	/* GDT tables in non default location kernel can be beyond 16MB and
	/*
	 * GDT tables in non default location kernel can be beyond 16MB and
	 * lgdt will not be able to load the address as in real mode default
	 * operand size is 16bit. Use lgdtl instead to force operand size
	 * to 32 bit.
	 */

	lidtl	boot_idt_descr		# load idt with 0, 0
	lgdtl	boot_gdt_descr		# load gdt with whatever is appropriate

	xor	%ax, %ax
	inc	%ax			# protected mode (PE) bit
	lmsw	%ax			# into protected mode
	movw	$1, %dx			# protected mode (PE) bit
	lmsw	%dx			# into protected mode

	# flush prefetch and jump to startup_32_smp in arch/i386/kernel/head.S
	ljmpl	*(startup_32_smp)
	ljmpl	$__BOOT_CS, $pa_startup_32

	.section ".text32","ax"
	.code32
ENTRY(startup_32)			# note: also used from wakeup_asm.S
	jmp	*%eax

	.data
	.globl startup_32_smp, boot_gdt, trampoline_status
@@ -82,5 +87,4 @@ trampoline_status:
	.long	0

startup_32_smp:
	.long	0x00000000
	.word	__BOOT_CS, 0
	.long	0
+5 −3
Original line number Diff line number Diff line
@@ -124,9 +124,11 @@ wakeup_start:
	lgdtl	pmode_gdt

	/* This really couldn't... */
	movl	pmode_cr0, %eax
	movl	%eax, %cr0
	ljmpl	*pmode_entry
	movl	pmode_entry, %eax
	movl	pmode_cr0, %ecx
	movl	%ecx, %cr0
	ljmpl	$__KERNEL_CS, $pa_startup_32
	/* -> jmp *%eax in trampoline_32.S */
#else
	jmp	trampoline_data
#endif