This is a note to let you know that I've just added the patch titled
x86/traps: Ignore high word of regs->cs in early_fixup_exception()
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-traps-ignore-high-word-of-regs-cs-in-early_fixup_exception.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From fc0e81b2bea0ebceb71889b61d2240856141c9ee Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Sat, 19 Nov 2016 18:42:40 -0800
Subject: x86/traps: Ignore high word of regs->cs in early_fixup_exception()
From: Andy Lutomirski <luto@xxxxxxxxxx>
commit fc0e81b2bea0ebceb71889b61d2240856141c9ee upstream.
On the 80486 DX, it seems that some exceptions may leave garbage in
the high bits of CS. This causes sporadic failures in which
early_fixup_exception() refuses to fix up an exception.
As far as I can tell, this has been buggy for a long time, but the
problem seems to have been exacerbated by commits:
1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
e1bfc11c5a6f ("x86/init: Fix cr4_init_shadow() on CR4-less machines")
This appears to have broken for as long as we've had early
exception handling.
[ This backport should apply to kernels from 3.4 - 4.5. ]
Fixes: 4c5023a3fa2e ("x86-32: Handle exception table entries during early boot")
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Reported-by: Matthew Whitehead <tedheadster@xxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/head_32.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -571,7 +571,7 @@ early_idt_handler_common:
movl %eax,%ds
movl %eax,%es
- cmpl $(__KERNEL_CS),32(%esp)
+ cmpw $(__KERNEL_CS),32(%esp)
jne 10f
leal 28(%esp),%eax # Pointer to %eip
Patches currently in stable-queue which might be from luto@xxxxxxxxxx are
queue-4.4/x86-traps-ignore-high-word-of-regs-cs-in-early_fixup_exception.patch
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