linux-kernel - Re: [PATCH 3.13 106/162] KVM: x86: Fix far-jump to non-canonical check

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Message-ID: <CAHTgTXXWqYd+wuDd+4_SAxFJO-beDrhJffXBB7fGz+PmeA0T3w@mail.gmail.com>
Date:	Mon, 29 Dec 2014 15:58:57 -0800
From:	Vinson Lee <vlee@...pensource.com>
To:	Kamal Mostafa <kamal@...onical.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com, Nadav Amit <namit@...technion.ac.il>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 3.13 106/162] KVM: x86: Fix far-jump to non-canonical check

On Thu, Nov 6, 2014 at 2:36 PM, Kamal Mostafa <kamal@...onical.com> wrote:
> 3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.
>
> ------------------
>
> From: Nadav Amit <namit@...technion.ac.il>
>
> commit 7e46dddd6f6cd5dbf3c7bd04a7e75d19475ac9f2 upstream.
>
> Commit d1442d85cc30 ("KVM: x86: Handle errors when RIP is set during far
> jumps") introduced a bug that caused the fix to be incomplete.  Due to
> incorrect evaluation, far jump to segment with L bit cleared (i.e., 32-bit
> segment) and RIP with any of the high bits set (i.e, RIP[63:32] != 0) set may
> not trigger #GP.  As we know, this imposes a security problem.
>
> In addition, the condition for two warnings was incorrect.
>
> Fixes: d1442d85cc30ea75f7d399474ca738e0bc96f715
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Nadav Amit <namit@...technion.ac.il>
> [Add #ifdef CONFIG_X86_64 to avoid complaints of undefined behavior. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> [ kamal: backport to 3.13-stable: omitted WARN_ON fixes (not in 3.13) ]
> Signed-off-by: Kamal Mostafa <kamal@...onical.com>
> ---
>  arch/x86/kvm/emulate.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index a440bea..4ae37e7 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -581,12 +581,14 @@ static inline int assign_eip_far(struct x86_emulate_ctxt *ctxt, ulong dst,
>         case 4:
>                 ctxt->_eip = (u32)dst;
>                 break;
> +#ifdef CONFIG_X86_64
>         case 8:
>                 if ((cs_l && is_noncanonical_address(dst)) ||
> -                   (!cs_l && (dst & ~(u32)-1)))
> +                   (!cs_l && (dst >> 32) != 0))
>                         return emulate_gp(ctxt, 0);
>                 ctxt->_eip = dst;
>                 break;
> +#endif
>         default:
>                 WARN(1, "unsupported eip assignment size\n");
>         }
> --
> 1.9.1
>
> --
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Hi.

Should the WARN_ON fixes have been included as well in 3.13.11.11?

WARN_ON hunks were added with the backport of "KVM: x86: Handle errors
when RIP is set during far jumps" in 3.13.11.11 commit
b8ba339d86fb627d54fea929492114d45f6835c2.

Cheers,
Vinson
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