Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 04/13] x86/traps: Ignore high word of regs->cs in early_fixup_exception() | Date | Wed, 7 Dec 2016 08:07:43 +0100 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Andy Lutomirski <luto@kernel.org>
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@zytor.com> Reported-by: Matthew Whitehead <tedheadster@gmail.com> Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- 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
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