[RFC] kvm - possible out of bounds

From	Geyslan Gregório Bem <geyslan@gmail.com>
Newsgroups	linux.kernel
Subject	[RFC] kvm - possible out of bounds
Date	2015-11-29 21:20 +0100
Message-ID	<qAgBY-2gb-11@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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Hello,

I have found a possible out of bounds reading in
arch/powerpc/kvm/book3s_64_mmu.c (kvmppc_mmu_book3s_64_xlate
function). pteg[] array could be accessed twice using the i variable
after the for iteration. What happens is that in the last iteration
the i index is incremented to 16, checked (i<16) then confirmed
exiting the loop.

277    for (i=0; i<16; i+=2) { ...

Later there are reading attempts to the pteg last elements, but using
again the already incremented i (16).

303    v = be64_to_cpu(pteg[i]);  /* pteg[16] */
304    r = be64_to_cpu(pteg[i+1]); /* pteg[17] */

I really don't know if the for lace will somehow iterate until i is
16, anyway I think that the last readings must be using a defined max
len/index or another more clear method.

Eg.

    v = be64_to_cpu(pteg[PTEG_LEN - 2]);
    r = be64_to_cpu(pteg[PTEG_LEN - 1]);

Or just.

    v = be64_to_cpu(pteg[14]);
    r = be64_to_cpu(pteg[15]);

----------------------------

I found in the same file a variable that is not used.

380    struct kvmppc_vcpu_book3s *vcpu_book3s;
...
387    vcpu_book3s = to_book3s(vcpu);

-----------------------------

A question, the kvmppc_mmu_book3s_64_init function is accessed by
unconventional way? Because I have not found any calling to it.

If something that I wrote is correct please tell me if I could send the patch.

-- 
Regards,

Geyslan G. Bem
hackingbits.com
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[RFC] kvm - possible out of bounds Geyslan Gregório Bem <geyslan@gmail.com> - 2015-11-29 21:20 +0100
  Re: [RFC] kvm - possible out of bounds Paul Mackerras <paulus@ozlabs.org> - 2015-11-29 22:40 +0100
    Re: [RFC] kvm - possible out of bounds Geyslan Gregório Bem <geyslan@gmail.com> - 2015-11-29 23:10 +0100

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