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Subject[tip:x86/trampoline] x86, realmode: Remove indirect jumps in trampoline_32 and wakeup_asm
Commit-ID:  968ff9ee56f1e3ed4ff4a6d10185865dc77d8f7e
Gitweb: http://git.kernel.org/tip/968ff9ee56f1e3ed4ff4a6d10185865dc77d8f7e
Author: H. Peter Anvin <hpa@linux.intel.com>
AuthorDate: Tue, 8 May 2012 21:22:36 +0300
Committer: H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Tue, 8 May 2012 11:48:03 -0700

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: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-14-git-send-email-jarkko.sakkinen@intel.com
---
arch/x86/realmode/rm/trampoline_32.S | 22 +++++++++++++---------
arch/x86/realmode/rm/wakeup/wakeup_asm.S | 8 +++++---
2 files changed, 18 insertions(+), 12 deletions(-)
diff --git a/arch/x86/realmode/rm/trampoline_32.S b/arch/x86/realmode/rm/trampoline_32.S
index 1f9e331..1315ef4 100644
--- a/arch/x86/realmode/rm/trampoline_32.S
+++ b/arch/x86/realmode/rm/trampoline_32.S
@@ -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
diff --git a/arch/x86/realmode/rm/wakeup/wakeup_asm.S b/arch/x86/realmode/rm/wakeup/wakeup_asm.S
index b61126c..4c5c5f2 100644
--- a/arch/x86/realmode/rm/wakeup/wakeup_asm.S
+++ b/arch/x86/realmode/rm/wakeup/wakeup_asm.S
@@ -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

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