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1================================2Application Data Integrity (ADI)3================================4 5SPARC M7 processor adds the Application Data Integrity (ADI) feature.6ADI allows a task to set version tags on any subset of its address7space. Once ADI is enabled and version tags are set for ranges of8address space of a task, the processor will compare the tag in pointers9to memory in these ranges to the version set by the application10previously. Access to memory is granted only if the tag in given pointer11matches the tag set by the application. In case of mismatch, processor12raises an exception.13 14Following steps must be taken by a task to enable ADI fully:15 161. Set the user mode PSTATE.mcde bit. This acts as master switch for17 the task's entire address space to enable/disable ADI for the task.18 192. Set TTE.mcd bit on any TLB entries that correspond to the range of20 addresses ADI is being enabled on. MMU checks the version tag only21 on the pages that have TTE.mcd bit set.22 233. Set the version tag for virtual addresses using stxa instruction24 and one of the MCD specific ASIs. Each stxa instruction sets the25 given tag for one ADI block size number of bytes. This step must26 be repeated for entire page to set tags for entire page.27 28ADI block size for the platform is provided by the hypervisor to kernel29in machine description tables. Hypervisor also provides the number of30top bits in the virtual address that specify the version tag. Once31version tag has been set for a memory location, the tag is stored in the32physical memory and the same tag must be present in the ADI version tag33bits of the virtual address being presented to the MMU. For example on34SPARC M7 processor, MMU uses bits 63-60 for version tags and ADI block35size is same as cacheline size which is 64 bytes. A task that sets ADI36version to, say 10, on a range of memory, must access that memory using37virtual addresses that contain 0xa in bits 63-60.38 39ADI is enabled on a set of pages using mprotect() with PROT_ADI flag.40When ADI is enabled on a set of pages by a task for the first time,41kernel sets the PSTATE.mcde bit for the task. Version tags for memory42addresses are set with an stxa instruction on the addresses using43ASI_MCD_PRIMARY or ASI_MCD_ST_BLKINIT_PRIMARY. ADI block size is44provided by the hypervisor to the kernel. Kernel returns the value of45ADI block size to userspace using auxiliary vector along with other ADI46info. Following auxiliary vectors are provided by the kernel:47 48 ============ ===========================================49 AT_ADI_BLKSZ ADI block size. This is the granularity and50 alignment, in bytes, of ADI versioning.51 AT_ADI_NBITS Number of ADI version bits in the VA52 ============ ===========================================53 54 55IMPORTANT NOTES56===============57 58- Version tag values of 0x0 and 0xf are reserved. These values match any59 tag in virtual address and never generate a mismatch exception.60 61- Version tags are set on virtual addresses from userspace even though62 tags are stored in physical memory. Tags are set on a physical page63 after it has been allocated to a task and a pte has been created for64 it.65 66- When a task frees a memory page it had set version tags on, the page67 goes back to free page pool. When this page is re-allocated to a task,68 kernel clears the page using block initialization ASI which clears the69 version tags as well for the page. If a page allocated to a task is70 freed and allocated back to the same task, old version tags set by the71 task on that page will no longer be present.72 73- ADI tag mismatches are not detected for non-faulting loads.74 75- Kernel does not set any tags for user pages and it is entirely a76 task's responsibility to set any version tags. Kernel does ensure the77 version tags are preserved if a page is swapped out to the disk and78 swapped back in. It also preserves that version tags if a page is79 migrated.80 81- ADI works for any size pages. A userspace task need not be aware of82 page size when using ADI. It can simply select a virtual address83 range, enable ADI on the range using mprotect() and set version tags84 for the entire range. mprotect() ensures range is aligned to page size85 and is a multiple of page size.86 87- ADI tags can only be set on writable memory. For example, ADI tags can88 not be set on read-only mappings.89 90 91 92ADI related traps93=================94 95With ADI enabled, following new traps may occur:96 97Disrupting memory corruption98----------------------------99 100 When a store accesses a memory location that has TTE.mcd=1,101 the task is running with ADI enabled (PSTATE.mcde=1), and the ADI102 tag in the address used (bits 63:60) does not match the tag set on103 the corresponding cacheline, a memory corruption trap occurs. By104 default, it is a disrupting trap and is sent to the hypervisor105 first. Hypervisor creates a sun4v error report and sends a106 resumable error (TT=0x7e) trap to the kernel. The kernel sends107 a SIGSEGV to the task that resulted in this trap with the following108 info::109 110 siginfo.si_signo = SIGSEGV;111 siginfo.errno = 0;112 siginfo.si_code = SEGV_ADIDERR;113 siginfo.si_addr = addr; /* PC where first mismatch occurred */114 siginfo.si_trapno = 0;115 116 117Precise memory corruption118-------------------------119 120 When a store accesses a memory location that has TTE.mcd=1,121 the task is running with ADI enabled (PSTATE.mcde=1), and the ADI122 tag in the address used (bits 63:60) does not match the tag set on123 the corresponding cacheline, a memory corruption trap occurs. If124 MCD precise exception is enabled (MCDPERR=1), a precise125 exception is sent to the kernel with TT=0x1a. The kernel sends126 a SIGSEGV to the task that resulted in this trap with the following127 info::128 129 siginfo.si_signo = SIGSEGV;130 siginfo.errno = 0;131 siginfo.si_code = SEGV_ADIPERR;132 siginfo.si_addr = addr; /* address that caused trap */133 siginfo.si_trapno = 0;134 135 NOTE:136 ADI tag mismatch on a load always results in precise trap.137 138 139MCD disabled140------------141 142 When a task has not enabled ADI and attempts to set ADI version143 on a memory address, processor sends an MCD disabled trap. This144 trap is handled by hypervisor first and the hypervisor vectors this145 trap through to the kernel as Data Access Exception trap with146 fault type set to 0xa (invalid ASI). When this occurs, the kernel147 sends the task SIGSEGV signal with following info::148 149 siginfo.si_signo = SIGSEGV;150 siginfo.errno = 0;151 siginfo.si_code = SEGV_ACCADI;152 siginfo.si_addr = addr; /* address that caused trap */153 siginfo.si_trapno = 0;154 155 156Sample program to use ADI157-------------------------158 159Following sample program is meant to illustrate how to use the ADI160functionality::161 162 #include <unistd.h>163 #include <stdio.h>164 #include <stdlib.h>165 #include <elf.h>166 #include <sys/ipc.h>167 #include <sys/shm.h>168 #include <sys/mman.h>169 #include <asm/asi.h>170 171 #ifndef AT_ADI_BLKSZ172 #define AT_ADI_BLKSZ 48173 #endif174 #ifndef AT_ADI_NBITS175 #define AT_ADI_NBITS 49176 #endif177 178 #ifndef PROT_ADI179 #define PROT_ADI 0x10180 #endif181 182 #define BUFFER_SIZE 32*1024*1024UL183 184 main(int argc, char* argv[], char* envp[])185 {186 unsigned long i, mcde, adi_blksz, adi_nbits;187 char *shmaddr, *tmp_addr, *end, *veraddr, *clraddr;188 int shmid, version;189 Elf64_auxv_t *auxv;190 191 adi_blksz = 0;192 193 while(*envp++ != NULL);194 for (auxv = (Elf64_auxv_t *)envp; auxv->a_type != AT_NULL; auxv++) {195 switch (auxv->a_type) {196 case AT_ADI_BLKSZ:197 adi_blksz = auxv->a_un.a_val;198 break;199 case AT_ADI_NBITS:200 adi_nbits = auxv->a_un.a_val;201 break;202 }203 }204 if (adi_blksz == 0) {205 fprintf(stderr, "Oops! ADI is not supported\n");206 exit(1);207 }208 209 printf("ADI capabilities:\n");210 printf("\tBlock size = %ld\n", adi_blksz);211 printf("\tNumber of bits = %ld\n", adi_nbits);212 213 if ((shmid = shmget(2, BUFFER_SIZE,214 IPC_CREAT | SHM_R | SHM_W)) < 0) {215 perror("shmget failed");216 exit(1);217 }218 219 shmaddr = shmat(shmid, NULL, 0);220 if (shmaddr == (char *)-1) {221 perror("shm attach failed");222 shmctl(shmid, IPC_RMID, NULL);223 exit(1);224 }225 226 if (mprotect(shmaddr, BUFFER_SIZE, PROT_READ|PROT_WRITE|PROT_ADI)) {227 perror("mprotect failed");228 goto err_out;229 }230 231 /* Set the ADI version tag on the shm segment232 */233 version = 10;234 tmp_addr = shmaddr;235 end = shmaddr + BUFFER_SIZE;236 while (tmp_addr < end) {237 asm volatile(238 "stxa %1, [%0]0x90\n\t"239 :240 : "r" (tmp_addr), "r" (version));241 tmp_addr += adi_blksz;242 }243 asm volatile("membar #Sync\n\t");244 245 /* Create a versioned address from the normal address by placing246 * version tag in the upper adi_nbits bits247 */248 tmp_addr = (void *) ((unsigned long)shmaddr << adi_nbits);249 tmp_addr = (void *) ((unsigned long)tmp_addr >> adi_nbits);250 veraddr = (void *) (((unsigned long)version << (64-adi_nbits))251 | (unsigned long)tmp_addr);252 253 printf("Starting the writes:\n");254 for (i = 0; i < BUFFER_SIZE; i++) {255 veraddr[i] = (char)(i);256 if (!(i % (1024 * 1024)))257 printf(".");258 }259 printf("\n");260 261 printf("Verifying data...");262 fflush(stdout);263 for (i = 0; i < BUFFER_SIZE; i++)264 if (veraddr[i] != (char)i)265 printf("\nIndex %lu mismatched\n", i);266 printf("Done.\n");267 268 /* Disable ADI and clean up269 */270 if (mprotect(shmaddr, BUFFER_SIZE, PROT_READ|PROT_WRITE)) {271 perror("mprotect failed");272 goto err_out;273 }274 275 if (shmdt((const void *)shmaddr) != 0)276 perror("Detach failure");277 shmctl(shmid, IPC_RMID, NULL);278 279 exit(0);280 281 err_out:282 if (shmdt((const void *)shmaddr) != 0)283 perror("Detach failure");284 shmctl(shmid, IPC_RMID, NULL);285 exit(1);286 }287