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147 lines
3.9 KiB
147 lines
3.9 KiB
/*
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* Copyright 2002-2019 Intel Corporation.
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*
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* This software is provided to you as Sample Source Code as defined in the accompanying
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* End User License Agreement for the Intel(R) Software Development Products ("Agreement")
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* section 1.L.
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*
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* This software and the related documents are provided as is, with no express or implied
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* warranties, other than those that are expressly stated in the License.
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*/
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#include <stdio.h>
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#include <pthread.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <syscall.h>
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#include <linux/unistd.h>
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#include <asm/ldt.h>
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#include <errno.h>
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#include <string.h>
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#include <sys/types.h>
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#define NTHREADS 4
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typedef struct {
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unsigned int entry_number;
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unsigned int base_addr;
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unsigned int limit;
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unsigned int seg_32bit:1;
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unsigned int contents:2;
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unsigned int read_exec_only:1;
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unsigned int limit_in_pages:1;
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unsigned int seg_not_present:1;
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unsigned int useable:1;
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}UserDesc;
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# define TLS_GET_GS_REG() \
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({ int __seg; __asm ("movw %%gs, %w0" : "=q" (__seg)); __seg & 0xffff; })
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# define TLS_SET_GS_REG(val) \
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__asm ("movw %w0, %%gs" :: "q" (val))
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#define LDT_GET 0
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#define LDT_SET 1
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#define FILL_ENTRIES 10
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struct LDT_TABLE_ENTRY
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{
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LDT_TABLE_ENTRY(): _val1(0), _val2(0) {}
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unsigned int _val1;
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unsigned int _val2;
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};
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inline unsigned int LDTEntryA(unsigned int base) { return base << 16; }
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char buf[NTHREADS][3000];
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void * thread_func (void *arg)
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{
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unsigned long thread_no = (unsigned long)arg+1;
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unsigned int gs_value = TLS_GET_GS_REG();
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sprintf(buf[thread_no-1],"gs value for thread %ld is 0x%x\n", thread_no, gs_value );
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LDT_TABLE_ENTRY ldtEntries[FILL_ENTRIES];
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unsigned int sizeInBytes = sizeof(LDT_TABLE_ENTRY)*FILL_ENTRIES;
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int res = syscall(SYS_modify_ldt, LDT_GET, ldtEntries, sizeInBytes);
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if (res != sizeInBytes)
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{
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printf("LDT_GET failed\n");
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return 0;
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}
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if (((gs_value >> 2)& 1) == 0)
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{
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sprintf(buf[thread_no-1],"%sGS points to GDT\n", buf[thread_no-1]);
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for (unsigned int i=0; i<FILL_ENTRIES; i++)
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{
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sprintf(buf[thread_no-1],"%sThread %d: LDT entry %d\n", buf[thread_no-1], thread_no, i);
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}
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}
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else
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{
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unsigned int entry = gs_value >> 3;
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if (LDTEntryA(entry) == ldtEntries[entry]._val1)
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{
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sprintf(buf[thread_no-1],"%sThread %d: original LDT entry %d\n", buf[thread_no-1], thread_no, entry);
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}
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else
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{
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sprintf(buf[thread_no-1],"%sThread %d: modified LDT entry %d\n", buf[thread_no-1], thread_no, entry);
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}
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}
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return 0;
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}
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int main (int argc, char *argv[])
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{
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pthread_t h[NTHREADS];
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UserDesc tr[FILL_ENTRIES];
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int res;
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memset(tr, 0, sizeof(UserDesc)*FILL_ENTRIES);
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unsigned long num = pthread_self();
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for (unsigned int i = 1; i < FILL_ENTRIES; i++)
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{
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tr[i].entry_number = i;
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tr[i].base_addr = i;
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res = syscall(SYS_modify_ldt, LDT_SET, &tr[i], sizeof(UserDesc));
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if (res < 0)
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{
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printf("main thread: LDT_GET for entry %d failed, code %d, %s\n", i, errno, strerror(errno) );
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}
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}
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LDT_TABLE_ENTRY ldtEntries[FILL_ENTRIES];
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unsigned int sizeInBytes = sizeof(LDT_TABLE_ENTRY)*FILL_ENTRIES;
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res = syscall(SYS_modify_ldt, LDT_GET, ldtEntries, sizeInBytes);
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if (res != sizeInBytes)
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{
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printf("LDT_GET failed\n");
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return 0;
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}
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for (unsigned int i = 1; i < FILL_ENTRIES; i++)
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{
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printf("ldt entry %d 0x%x \n", i, ldtEntries[i]._val1);
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}
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printf("Original GS for the main thread is 0x%x\n", TLS_GET_GS_REG() );
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for (unsigned long i = 0; i < NTHREADS; i++)
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{
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pthread_create (&h[i], 0, thread_func, (void *)i);
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}
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for (unsigned long i = 0; i < NTHREADS; i++)
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{
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pthread_join (h[i], 0);
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}
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for (unsigned long i = 0; i < NTHREADS; i++)
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{
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printf("%s", buf[i]);
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}
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}
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