Re: [PATCH] kvm-kmod: x86: make sure kvm_get_desc_base() doesn't sign extend

[Jan Kiszka <jan.kiszka@web.de>]

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Am 12.10.2010 17:28, Bernhard Kohl wrote:
> The current implementation of kvm_get_desc_base() sign extends the
> return value because of integer promotion rules when compiled for
> x86_64 kernels. For the most part, this doesn't matter, because
> the top bit of base2 is usually 0. If, however, that bit is 1, then
> the entire value will be 0xffff... which is probably not what the
> caller intended.
> 
> We have a legacy OS which runs into errors in certain situations
> (task switches) because of this bug, i.e. error on vm_entry followed
> by unhandled vm_exit.
> 
> dmesg says:
> vmx_handle_exit: unexpected, valid vectoring info (0x80000b0d)
> and exit reason is 0x80000021
> or
> vmx_handle_exit: unexpected, valid vectoring info (0x80000300)
> and exit reason is 0x80000021
> 
> qemu-kvm says:
> kvm: unhandled exit 80000021
> kvm_run returned -22
> 
> This fix was originally applied as patch 2c75910 in kvm.git:
> "x86: Make sure get_user_desc() doesn't sign extend."
> 
> Signed-off-by: Bernhard Kohl <bernhard.kohl@nsn.com>
> ---
>  x86/external-module-compat.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/x86/external-module-compat.h b/x86/external-module-compat.h
> index 15b0280..a2af776 100644
> --- a/x86/external-module-compat.h
> +++ b/x86/external-module-compat.h
> @@ -435,7 +435,7 @@ struct kvm_desc_ptr {
>  static inline unsigned long
>  kvm_get_desc_base(const struct kvm_desc_struct *desc)
>  {
> -	return desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24);
> +	return (unsigned)(desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24));
>  }
>  
>  static inline void

Merged, thanks!

Jan


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