Sean Christopherson 8764ed55c9 KVM: x86: Whitelist port 0x7e for pre-incrementing %rip ... KVM's recent bug fix to update %rip after emulating I/O broke userspace that relied on the previous behavior of incrementing %rip prior to exiting to userspace. When running a Windows XP guest on AMD hardware, Qemu may patch "OUT 0x7E" instructions in reaction to the OUT itself. Because KVM's old behavior was to increment %rip before exiting to userspace to handle the I/O, Qemu manually adjusted %rip to account for the OUT instruction. Arguably this is a userspace bug as KVM requires userspace to re-enter the kernel to complete instruction emulation before taking any other actions. That being said, this is a bit of a grey area and breaking userspace that has worked for many years is bad. Pre-increment %rip on OUT to port 0x7e before exiting to userspace to hack around the issue. Fixes: 45def77ebf ("KVM: x86: update %rip after emulating IO") Reported-by: Simon Becherer <simon@becherer.de> Reported-and-tested-by: Iakov Karpov <srid@rkmail.ru> Reported-by: Gabriele Balducci <balducci@units.it> Reported-by: Antti Antinoja <reader@fennosys.fi> Cc: stable@vger.kernel.org Cc: Takashi Iwai <tiwai@suse.com> Cc: Jiri Slaby <jslaby@suse.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>		2019-04-30 21:03:42 +02:00
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asm	KVM: x86: Whitelist port 0x7e for pre-incrementing %rip	2019-04-30 21:03:42 +02:00