| 1 | /** |
| 2 | * This file has no copyright assigned and is placed in the Public Domain. |
| 3 | * This file is part of the mingw-w64 runtime package. |
| 4 | * No warranty is given; refer to the file DISCLAIMER.PD within this package. |
| 5 | */ |
| 6 | |
| 7 | // This source file defines the function pointers required to support Control |
| 8 | // Flow Guard. They shall be included even if CFGuard is disabled when building |
| 9 | // mingw-w64-crt itself, to allow linking to objects/libraries compiled with |
| 10 | // CFGuard. |
| 11 | |
| 12 | #if defined(__x86_64__) |
| 13 | |
| 14 | // The target address is passed as a parameter in an arch-specific manner, |
| 15 | // however it is not specified how on x86_64 because __guard_dispatch_icall_fptr |
| 16 | // is used instead. My guess would be that it's passed on %rcx, but it doesn't |
| 17 | // really matter here because this is a no-op anyway. |
| 18 | static void __guard_check_icall_dummy(void) {} |
| 19 | |
| 20 | // This is intentionally declared as _not_ a function pointer, so that the |
| 21 | // jmp instruction is not included as a valid call target for CFGuard. |
| 22 | extern void *__guard_dispatch_icall_dummy; |
| 23 | |
| 24 | #elif defined(__i386__) || defined(__aarch64__) || defined(__arm__) |
| 25 | |
| 26 | // The target address is passed via %ecx (x86), X15 (aarch64) or R0 (arm), |
| 27 | // but it doesn't really matter here because this is a no-op anyway. |
| 28 | static void __guard_check_icall_dummy(void) {} |
| 29 | |
| 30 | #else |
| 31 | # error "CFGuard support is unimplemented for the current architecture." |
| 32 | #endif |
| 33 | |
| 34 | // I am not sure about the `.00cfg` section. This is just an attempt to follow |
| 35 | // what VC runtime defines -- it places all the guard check function pointers |
| 36 | // inside this section. The MSVC linker appears to merge this section into |
| 37 | // `.rdata`, but LLD does not do this at the time of writing. |
| 38 | // This section should be readonly data. The only thing that modifies these |
| 39 | // pointers is the PE image loader. |
| 40 | |
| 41 | __asm__(".section .00cfg,\"dr\""); |
| 42 | |
| 43 | __attribute__(( section (".00cfg") )) |
| 44 | void *__guard_check_icall_fptr = &__guard_check_icall_dummy; |
| 45 | |
| 46 | #if defined(__x86_64__) |
| 47 | |
| 48 | __attribute__(( section (".00cfg") )) |
| 49 | void *__guard_dispatch_icall_fptr = &__guard_dispatch_icall_dummy; |
| 50 | |
| 51 | #endif |