Ofufuza ochokera m'mayunivesite angapo ku US ndi Australia apanga ziwopsezo ziwiri za Rowhammer-class—GDDRHammer ndi GeForge—zomwe zimalola kuwonongeka kwa ma bits amtundu uliwonse mu ma chips a memory a GDDR pochita CUDA kernel yopanda ufulu pa NVIDIA GPU. Mosiyana ndi njira ya GPUHammer yomwe idaperekedwa chaka chatha, ziwopsezo zatsopanozi sizimangokhudza deta yomwe imakonzedwa mu GPU memory koma zimalola mwayi wonse wopeza memory yonse yayikulu mkati mwa malo a adilesi ya CPU. Ofufuzawo adawonetsa zogwiritsa ntchito zomwe zimapatsa mwayi wolowera mu system ya host pochita CUDA kernel yopanda ufulu pa GPU.
Kuukira konseku kumawononga maselo okumbukira makanema omwe owukirawo alibe mwayi wowafikira mwachindunji, zomwe zimapangitsa kuti zinthu zomwe zili m'maselowo zisinthe. Kuwerenga ndi kulemba ku kukumbukira mkati mwa malo a adilesi ya CPU kumachitika mwa kusokoneza GPU memory allocator (cudaMalloc) kuti iwononge GPU memory integration ndikuyika ma adilesi enieni a GPU ku ma adilesi osadziwika mu GPU kapena CPU memory yeniyeni.
Kuukira kumeneku kumachitika powononga ma bit values mu video memory, yomwe imasunga matebulo a tsamba la GPU omwe ali ndi udindo womasulira ma adilesi enieni kukhala enieni. Kusiyana pakati pa kuukira kwa GDDRHammer ndi GeForge ndikuti njira ya GDDRHammer imasintha Last Level Page Table (PT), pomwe njira ya GeForge imasintha Last Level Page Directory (PD0).
Pakati pa zinthu zina, matebulo omasulira adilesi omwe atchulidwa amagwiritsidwa ntchito kukonza mwayi wolowera mwachindunji wa GPU ku memory ya CPU, motero, kusintha adilesi mu tebulo la tsamba la GPU kukhala adilesi yeniyeni mu RAM yayikulu ndikukhazikitsa mbendera ya APERTURE, yomwe imathandizira ma module a memory a CPU, zimapangitsa kuti zikhale zotheka kuwerenga ndikulemba deta yofikira memory yayikulu kudzera mu PCIe bus ndi IOMMU yozimitsidwa (yozimitsidwa mwachisawawa).
Kuukira kopambana kunawonetsedwa motsutsana ndi makadi ojambula aukadaulo a NVIDIA RTX A6000 ogwira ntchito kwambiri kutengera kapangidwe ka Ampere (makadi atsopano amayambira pa $6850, pomwe ogwiritsidwa ntchito amayambira pa $4000) ndi mitundu ya NVIDIA RTX 3060 ya ogula ($250-$300). Njira yopangidwa yopewera chitetezo cha Rowhammer, kuphatikiza kugwiritsa ntchito mphamvu za GPU zofananira, idalola kuwonjezeka kwa kuchuluka kwa kuwonongeka kwa maselo ka 64 poyerekeza ndi kuukira kwapitako. Monga njira yakanthawi yoletsera kuukira, njira ya Error Correcting Codes (ECC) ikhoza kuyatsidwa pogwiritsa ntchito lamulo la "nvidia-smi -e 1", koma izi zimayambitsa ndalama zowonjezera ndipo zitha kupewedwa pogwiritsa ntchito njira zowukira monga ECCploit ndi ECC.fail.
Kuwukira kwa RowHammer kumalola kusokoneza zomwe zili m'magawo amtundu wa DRAM powerenga mozungulira deta kuchokera kumaselo okumbukira oyandikana nawo. Popeza kukumbukira kwa DRAM ndi maselo amitundu iwiri, iliyonse yomwe imakhala ndi capacitor ndi transistor, kuwerengera kosalekeza kwa dera lomwelo la kukumbukira kumabweretsa kusinthasintha kwamagetsi ndi zolakwika, zomwe zimapangitsa kuchepa pang'ono kwa ma cell oyandikana nawo. Ngati kuchuluka kwa kuwerenga kuli kwakukulu, ndiye kuti selo loyandikana nalo likhoza kutaya ndalama zambiri zokwanira kuti ulendo wotsitsimula wotsatira usakhale ndi nthawi yobwezeretsa chikhalidwe chake choyambirira, chomwe chidzatsogolera kusintha kwa mtengo wa deta yosungidwa mu selo.
Njira yowukira ya Rowhammer idaperekedwa mu 2014, zomwe zidayambitsa masewera a paka ndi mbewa pakati pa ofufuza zachitetezo ndi opanga zida: opanga ma memory chip anayesa kuletsa kufooka, pomwe ofufuza adapeza njira zatsopano zopewera. Mwachitsanzo, kuti ateteze ku Rowhammer, opanga ma chip adawonjezera njira ya TRR (Target Row Refresh), koma zidapezeka kuti izi zidaletsa kuwonongeka kwa maselo m'milandu inayake ndipo sizinateteze ku zochitika zonse zomwe zingachitike. Njira zowukira zidapangidwa za ma DDR3, DDR4, ndi DDR5 chips pamakompyuta omwe ali ndi ma processor a Intel, AMD, ndi ARM, komanso kukumbukira kwa GDDR mu ma GPU a NVIDIA. Kuphatikiza apo, njira zinapezeka kuti zidutse kukonza zolakwika za ECC, ndipo njira zowukira zidaperekedwa pa ziwopsezo za netiweki komanso pogwiritsa ntchito JavaScript code mu msakatuli.
Source: opennet.ru
