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KVM: emulate: fix CMPXCHG8B on 32-bit hosts

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This has been broken for a long time: it broke first in 2.6.35, then was
almost fixed in 2.6.36 but this one-liner slipped through the cracks.
The bug shows up as an infinite loop in Windows 7 (and newer) boot on
32-bit hosts without EPT.

Windows uses CMPXCHG8B to write to page tables, which causes a
page fault if running without EPT; the emulator is then called from
kvm_mmu_page_fault.  The loop then happens if the higher 4 bytes are
not 0; the common case for this is that the NX bit (bit 63) is 1.

Fixes: 6550e1f165
Fixes: 16518d5ada
Cc: stable@vger.kernel.org   # 2.6.35+
Reported-by: Erik Rull <erik.rull@rdsoftware.de>
Tested-by: Erik Rull <erik.rull@rdsoftware.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-02-12 17:04:47 +01:00
parent 21bc8dc5b7
commit 4ff6f8e61e
1 changed files with 2 additions and 1 deletions
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3
arch/x86/kvm/emulate.c
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@ -4950,7 +4950,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
goto done;
}
}
ctxt->dst.orig_val = ctxt->dst.val;
/* Copy full 64-bit value for CMPXCHG8B. */
ctxt->dst.orig_val64 = ctxt->dst.val64;
special_insn: