60 lines
2.2 KiB
C
60 lines
2.2 KiB
C
/**
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* This file has no copyright assigned and is placed in the Public Domain.
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* This file is part of the mingw-w64 runtime package.
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* No warranty is given; refer to the file DISCLAIMER.PD within this package.
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*/
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// This source file defines the function pointers required to support Control
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// Flow Guard. They shall be included even if CFGuard is disabled when building
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// mingw-w64-crt itself, to allow linking to objects/libraries compiled with
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// CFGuard.
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#if defined(__x86_64__)
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// The target address is passed as a parameter in an arch-specific manner,
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// however it is not specified how on x86_64 because __guard_dispatch_icall_fptr
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// is used instead. My guess would be that it's passed on %rcx, but it doesn't
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// really matter here because this is a no-op anyway.
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static void __guard_check_icall_dummy(void) {}
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// When CFGuard is not active, directly tail-call the target address, which
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// is passed via %rax.
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__asm__(
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".globl __guard_dispatch_icall_dummy\n"
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"__guard_dispatch_icall_dummy:\n"
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" jmp *%rax\n"
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);
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// This is intentionally declared as _not_ a function pointer, so that the
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// jmp instruction is not included as a valid call target for CFGuard.
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extern void *__guard_dispatch_icall_dummy;
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#elif defined(__i386__) || defined(__aarch64__) || defined(__arm__)
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// The target address is passed via %ecx (x86), X15 (aarch64) or R0 (arm),
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// but it doesn't really matter here because this is a no-op anyway.
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static void __guard_check_icall_dummy(void) {}
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#else
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# error "CFGuard support is unimplemented for the current architecture."
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#endif
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// I am not sure about the `.00cfg` section. This is just an attempt to follow
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// what VC runtime defines -- it places all the guard check function pointers
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// inside this section. The MSVC linker appears to merge this section into
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// `.rdata`, but LLD does not do this at the time of writing.
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// This section should be readonly data. The only thing that modifies these
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// pointers is the PE image loader.
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__asm__(".section .00cfg,\"dr\"");
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__attribute__(( section (".00cfg") ))
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void *__guard_check_icall_fptr = &__guard_check_icall_dummy;
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#if defined(__x86_64__)
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__attribute__(( section (".00cfg") ))
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void *__guard_dispatch_icall_fptr = &__guard_dispatch_icall_dummy;
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#endif
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