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x86, realmode: Remove indirect jumps in trampoline_32 and wakeup_asm

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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: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-14-git-send-email-jarkko.sakkinen@intel.com
This commit is contained in:
H. Peter Anvin 2012-05-08 21:22:36 +03:00
parent 056a43a6d3
commit 968ff9ee56
2 changed files with 18 additions and 12 deletions
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22
arch/x86/realmode/rm/trampoline_32.S
View File

@ -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

8
arch/x86/realmode/rm/wakeup/wakeup_asm.S
View File

@ -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