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February 19, 2016 07:17
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My totally working attempt at hooking 8 byte functions
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| #include "sys/mman.h" | |
| void tiny_hook(uint32_t* addr, uint32_t hook) { | |
| bool thumb = (uint32_t)addr & 1; | |
| if(thumb) | |
| addr = (uint32_t*) ((uint32_t) addr - 1); | |
| mprotect(addr, 9, PROT_READ | PROT_WRITE); | |
| *addr = (uint32_t) (thumb)? 0xF000F8DF : 0xE51FF008; // LDR PC, [PC] on Thumb and LDR PC, [PC, #-8] on ARM. | |
| *(addr + 1) = hook; | |
| mprotect(addr, 9, PROT_READ | PROT_EXEC); | |
| } |
There, fixed everything except the pagealigning for now.
Also decrementing addr for thumb before calling the first mprotect so that it changes write access to the same bytes as the second mprotect.
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When calling mprotect, the values must be aligned with page boundaries, so this code seems like it won't work. (The page containing addr will obviously be executable already, and may be writable too - so perhaps it will work in some cases.) You're also incrementing addr before calling mprotect the second time.