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| -rw-r--r-- | Documentation/sparc/adi.txt | 278 |
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diff --git a/Documentation/sparc/adi.txt b/Documentation/sparc/adi.txt new file mode 100644 index 000000000..e1aed155f --- /dev/null +++ b/Documentation/sparc/adi.txt @@ -0,0 +1,278 @@ +Application Data Integrity (ADI) +================================ + +SPARC M7 processor adds the Application Data Integrity (ADI) feature. +ADI allows a task to set version tags on any subset of its address +space. Once ADI is enabled and version tags are set for ranges of +address space of a task, the processor will compare the tag in pointers +to memory in these ranges to the version set by the application +previously. Access to memory is granted only if the tag in given pointer +matches the tag set by the application. In case of mismatch, processor +raises an exception. + +Following steps must be taken by a task to enable ADI fully: + +1. Set the user mode PSTATE.mcde bit. This acts as master switch for + the task's entire address space to enable/disable ADI for the task. + +2. Set TTE.mcd bit on any TLB entries that correspond to the range of + addresses ADI is being enabled on. MMU checks the version tag only + on the pages that have TTE.mcd bit set. + +3. Set the version tag for virtual addresses using stxa instruction + and one of the MCD specific ASIs. Each stxa instruction sets the + given tag for one ADI block size number of bytes. This step must + be repeated for entire page to set tags for entire page. + +ADI block size for the platform is provided by the hypervisor to kernel +in machine description tables. Hypervisor also provides the number of +top bits in the virtual address that specify the version tag. Once +version tag has been set for a memory location, the tag is stored in the +physical memory and the same tag must be present in the ADI version tag +bits of the virtual address being presented to the MMU. For example on +SPARC M7 processor, MMU uses bits 63-60 for version tags and ADI block +size is same as cacheline size which is 64 bytes. A task that sets ADI +version to, say 10, on a range of memory, must access that memory using +virtual addresses that contain 0xa in bits 63-60. + +ADI is enabled on a set of pages using mprotect() with PROT_ADI flag. +When ADI is enabled on a set of pages by a task for the first time, +kernel sets the PSTATE.mcde bit fot the task. Version tags for memory +addresses are set with an stxa instruction on the addresses using +ASI_MCD_PRIMARY or ASI_MCD_ST_BLKINIT_PRIMARY. ADI block size is +provided by the hypervisor to the kernel. Kernel returns the value of +ADI block size to userspace using auxiliary vector along with other ADI +info. Following auxiliary vectors are provided by the kernel: + + AT_ADI_BLKSZ ADI block size. This is the granularity and + alignment, in bytes, of ADI versioning. + AT_ADI_NBITS Number of ADI version bits in the VA + + +IMPORTANT NOTES: + +- Version tag values of 0x0 and 0xf are reserved. These values match any + tag in virtual address and never generate a mismatch exception. + +- Version tags are set on virtual addresses from userspace even though + tags are stored in physical memory. Tags are set on a physical page + after it has been allocated to a task and a pte has been created for + it. + +- When a task frees a memory page it had set version tags on, the page + goes back to free page pool. When this page is re-allocated to a task, + kernel clears the page using block initialization ASI which clears the + version tags as well for the page. If a page allocated to a task is + freed and allocated back to the same task, old version tags set by the + task on that page will no longer be present. + +- ADI tag mismatches are not detected for non-faulting loads. + +- Kernel does not set any tags for user pages and it is entirely a + task's responsibility to set any version tags. Kernel does ensure the + version tags are preserved if a page is swapped out to the disk and + swapped back in. It also preserves that version tags if a page is + migrated. + +- ADI works for any size pages. A userspace task need not be aware of + page size when using ADI. It can simply select a virtual address + range, enable ADI on the range using mprotect() and set version tags + for the entire range. mprotect() ensures range is aligned to page size + and is a multiple of page size. + +- ADI tags can only be set on writable memory. For example, ADI tags can + not be set on read-only mappings. + + + +ADI related traps +----------------- + +With ADI enabled, following new traps may occur: + +Disrupting memory corruption + + When a store accesses a memory localtion that has TTE.mcd=1, + the task is running with ADI enabled (PSTATE.mcde=1), and the ADI + tag in the address used (bits 63:60) does not match the tag set on + the corresponding cacheline, a memory corruption trap occurs. By + default, it is a disrupting trap and is sent to the hypervisor + first. Hypervisor creates a sun4v error report and sends a + resumable error (TT=0x7e) trap to the kernel. The kernel sends + a SIGSEGV to the task that resulted in this trap with the following + info: + + siginfo.si_signo = SIGSEGV; + siginfo.errno = 0; + siginfo.si_code = SEGV_ADIDERR; + siginfo.si_addr = addr; /* PC where first mismatch occurred */ + siginfo.si_trapno = 0; + + +Precise memory corruption + + When a store accesses a memory location that has TTE.mcd=1, + the task is running with ADI enabled (PSTATE.mcde=1), and the ADI + tag in the address used (bits 63:60) does not match the tag set on + the corresponding cacheline, a memory corruption trap occurs. If + MCD precise exception is enabled (MCDPERR=1), a precise + exception is sent to the kernel with TT=0x1a. The kernel sends + a SIGSEGV to the task that resulted in this trap with the following + info: + + siginfo.si_signo = SIGSEGV; + siginfo.errno = 0; + siginfo.si_code = SEGV_ADIPERR; + siginfo.si_addr = addr; /* address that caused trap */ + siginfo.si_trapno = 0; + + NOTE: ADI tag mismatch on a load always results in precise trap. + + +MCD disabled + + When a task has not enabled ADI and attempts to set ADI version + on a memory address, processor sends an MCD disabled trap. This + trap is handled by hypervisor first and the hypervisor vectors this + trap through to the kernel as Data Access Exception trap with + fault type set to 0xa (invalid ASI). When this occurs, the kernel + sends the task SIGSEGV signal with following info: + + siginfo.si_signo = SIGSEGV; + siginfo.errno = 0; + siginfo.si_code = SEGV_ACCADI; + siginfo.si_addr = addr; /* address that caused trap */ + siginfo.si_trapno = 0; + + +Sample program to use ADI +------------------------- + +Following sample program is meant to illustrate how to use the ADI +functionality. + +#include <unistd.h> +#include <stdio.h> +#include <stdlib.h> +#include <elf.h> +#include <sys/ipc.h> +#include <sys/shm.h> +#include <sys/mman.h> +#include <asm/asi.h> + +#ifndef AT_ADI_BLKSZ +#define AT_ADI_BLKSZ 48 +#endif +#ifndef AT_ADI_NBITS +#define AT_ADI_NBITS 49 +#endif + +#ifndef PROT_ADI +#define PROT_ADI 0x10 +#endif + +#define BUFFER_SIZE 32*1024*1024UL + +main(int argc, char* argv[], char* envp[]) +{ + unsigned long i, mcde, adi_blksz, adi_nbits; + char *shmaddr, *tmp_addr, *end, *veraddr, *clraddr; + int shmid, version; + Elf64_auxv_t *auxv; + + adi_blksz = 0; + + while(*envp++ != NULL); + for (auxv = (Elf64_auxv_t *)envp; auxv->a_type != AT_NULL; auxv++) { + switch (auxv->a_type) { + case AT_ADI_BLKSZ: + adi_blksz = auxv->a_un.a_val; + break; + case AT_ADI_NBITS: + adi_nbits = auxv->a_un.a_val; + break; + } + } + if (adi_blksz == 0) { + fprintf(stderr, "Oops! ADI is not supported\n"); + exit(1); + } + + printf("ADI capabilities:\n"); + printf("\tBlock size = %ld\n", adi_blksz); + printf("\tNumber of bits = %ld\n", adi_nbits); + + if ((shmid = shmget(2, BUFFER_SIZE, + IPC_CREAT | SHM_R | SHM_W)) < 0) { + perror("shmget failed"); + exit(1); + } + + shmaddr = shmat(shmid, NULL, 0); + if (shmaddr == (char *)-1) { + perror("shm attach failed"); + shmctl(shmid, IPC_RMID, NULL); + exit(1); + } + + if (mprotect(shmaddr, BUFFER_SIZE, PROT_READ|PROT_WRITE|PROT_ADI)) { + perror("mprotect failed"); + goto err_out; + } + + /* Set the ADI version tag on the shm segment + */ + version = 10; + tmp_addr = shmaddr; + end = shmaddr + BUFFER_SIZE; + while (tmp_addr < end) { + asm volatile( + "stxa %1, [%0]0x90\n\t" + : + : "r" (tmp_addr), "r" (version)); + tmp_addr += adi_blksz; + } + asm volatile("membar #Sync\n\t"); + + /* Create a versioned address from the normal address by placing + * version tag in the upper adi_nbits bits + */ + tmp_addr = (void *) ((unsigned long)shmaddr << adi_nbits); + tmp_addr = (void *) ((unsigned long)tmp_addr >> adi_nbits); + veraddr = (void *) (((unsigned long)version << (64-adi_nbits)) + | (unsigned long)tmp_addr); + + printf("Starting the writes:\n"); + for (i = 0; i < BUFFER_SIZE; i++) { + veraddr[i] = (char)(i); + if (!(i % (1024 * 1024))) + printf("."); + } + printf("\n"); + + printf("Verifying data..."); + fflush(stdout); + for (i = 0; i < BUFFER_SIZE; i++) + if (veraddr[i] != (char)i) + printf("\nIndex %lu mismatched\n", i); + printf("Done.\n"); + + /* Disable ADI and clean up + */ + if (mprotect(shmaddr, BUFFER_SIZE, PROT_READ|PROT_WRITE)) { + perror("mprotect failed"); + goto err_out; + } + + if (shmdt((const void *)shmaddr) != 0) + perror("Detach failure"); + shmctl(shmid, IPC_RMID, NULL); + + exit(0); + +err_out: + if (shmdt((const void *)shmaddr) != 0) + perror("Detach failure"); + shmctl(shmid, IPC_RMID, NULL); + exit(1); +} |