On 19.12.2019 12:43, Jan Beulich wrote:
> On 19.12.2019 10:42, Alexandru Stefan ISAILA wrote:
>> This patch aims to sanitize indexes, potentially guest provided
>> values, for altp2m_eptp[] and altp2m_p2m[] arrays.
>>
>> Requested-by: Jan Beulich <jbeul...@suse.com>
>> Signed-off-by: Alexandru Isaila <aisa...@bitdefender.com>
>> ---
>> CC: Razvan Cojocaru <rcojoc...@bitdefender.com>
>> CC: Tamas K Lengyel <ta...@tklengyel.com>
>> CC: Petre Pircalabu <ppircal...@bitdefender.com>
>> CC: George Dunlap <george.dun...@eu.citrix.com>
>> CC: Jan Beulich <jbeul...@suse.com>
>> CC: Andrew Cooper <andrew.coop...@citrix.com>
>> CC: Wei Liu <w...@xen.org>
>> CC: "Roger Pau Monné" <roger....@citrix.com>
>> CC: Jun Nakajima <jun.nakaj...@intel.com>
>> CC: Kevin Tian <kevin.t...@intel.com>
>> ---
>> Changes since V4:
>> - Change bounds check from MAX_EPTP to MAX_ALTP2M
>> - Move array_index_nospec() closer to the bounds check.
>> ---
>> xen/arch/x86/mm/mem_access.c | 15 +++++++++------
>> xen/arch/x86/mm/p2m.c | 20 ++++++++++++++------
>> 2 files changed, 23 insertions(+), 12 deletions(-)
>>
>> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
>> index 320b9fe621..33e379db8f 100644
>> --- a/xen/arch/x86/mm/mem_access.c
>> +++ b/xen/arch/x86/mm/mem_access.c
>> @@ -367,10 +367,11 @@ long p2m_set_mem_access(struct domain *d, gfn_t gfn,
>> uint32_t nr,
>> if ( altp2m_idx )
>> {
>> if ( altp2m_idx >= MAX_ALTP2M ||
Ok, so have if ( altp2m_idx >= min(ARRAY_SIZE(d->arch.altp2m_eptp),
MAX_EPTP) ||
here and then...
>> - d->arch.altp2m_eptp[altp2m_idx] == mfn_x(INVALID_MFN) )
>> + d->arch.altp2m_eptp[array_index_nospec(altp2m_idx,
>> MAX_ALTP2M)] ==
have MAX_EPTP here and ...
>
> As implied by a reply to v4, this is still latently buggy: There's
> no guarantee anyone will notice the issue here when bumping
> MAX_ALTP2M past MAX_EPTP. The only future proof thing to do here
> is, as suggested, using some form of min(MAX_ALTP2M, MAX_EPTP) in
> the actual bounds check. Then each array access itself can be made
> use the correct bound. In fact you'd probably have noticed this if
> you had made use of array_access_nospec() where possible (which
> also would help readability) - apparently not here, but ... >
>> + mfn_x(INVALID_MFN) )
>> return -EINVAL;
>>
>> - ap2m = d->arch.altp2m_p2m[altp2m_idx];
>> + ap2m = d->arch.altp2m_p2m[array_index_nospec(altp2m_idx,
>> MAX_ALTP2M)];
MAX_ALTP2M here ?
Alex
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