[PATCH] D59780: Support Intel Control-flow Enforcement Technology

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

@xiangzhangllvm The patch has been rebased, but it doesn't seem to work.

I made a local patch to make --require-cet behave more like --force-bti:

  --- i/lld/ELF/Driver.cpp
  +++ w/lld/ELF/Driver.cpp
  @@ -1705,2 +1705,4 @@ template <class ELFT> static uint32_t getAndFeatures() {
  -    } else if (!features && config->requireCET)
  -      error(toString(f) + ": --require-cet: file is not compatible with CET");
  +    } else if (config->requireCET && !(features & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
  +      warn(toString(f) + ": --require-cet: file is not compatible with CET");
  +      features |= GNU_PROPERTY_X86_FEATURE_1_IBT;
  +    }

I tried a trivial program with 2 PLT calls.

  gcc -fcf-protection=full -c a.c
  gcc -fcf-protection=full a.c -o a '-###'   # Retrieve linker command line, replace ld with 

My GCC crt files are not CET compatible but I think that is probably irrelevant.

  % ld.lld --eh-frame-hdr -m elf_x86_64 "--hash-style=gnu" -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie -o a /usr/lib/gcc/x86_64-linux-gnu/8/../../
  ../x86_64-linux-gnu/Scrt1.o /usr/lib/gcc/x86_64-linux-gnu/8/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/8/crtbeginS.o -L/usr/lib/gc
  c/x86_64-linux-gnu/8 -L/usr/lib/gcc/x86_64-linux-gnu/8/../../../x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/8/../../../../lib -L/lib/x86_64-linux
  -gnu -L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/8/../../.. a.o -lgcc --push-state --as-needed -lgcc_s
   --pop-state -lc -lgcc --push-state --as-needed -lgcc_s --pop-state /usr/lib/gcc/x86_64-linux-gnu/8/crtendS.o /usr/lib/gcc/x86_64-linux-gnu/8/../../..
  /x86_64-linux-gnu/crtn.o --require-cet -o a                                                                                                          
  ld.lld: warning: /usr/lib/gcc/x86_64-linux-gnu/8/../../../x86_64-linux-gnu/Scrt1.o: --require-cet: file is not compatible with CET
  ld.lld: warning: /usr/lib/gcc/x86_64-linux-gnu/8/../../../x86_64-linux-gnu/crti.o: --require-cet: file is not compatible with CET
  ld.lld: warning: /usr/lib/gcc/x86_64-linux-gnu/8/crtbeginS.o: --require-cet: file is not compatible with CET
  ld.lld: warning: /usr/lib/x86_64-linux-gnu/libc_nonshared.a(elf-init.oS): --require-cet: file is not compatible with CET
  ld.lld: warning: /usr/lib/gcc/x86_64-linux-gnu/8/crtendS.o: --require-cet: file is not compatible with CET
  ld.lld: warning: /usr/lib/gcc/x86_64-linux-gnu/8/../../../x86_64-linux-gnu/crtn.o: --require-cet: file is not compatible with CET

OK, it segfaults. So there may be some issues in the PLT.

  ./a => segmentation fault

Peter Smith implemented `--force-bti` for AArch64 in D62609 <https://reviews.llvm.org/D62609>. 
Its semantic is:

> --force-bti : Act as if all relocatable inputs had GNU_PROPERTY_AARCH64_FEATURE_1_BTI and warn for every relocatable object that does not.

Do you think it makes more sense to change `--require-cet` to `--force-cet` or `--force-ibt`?

There is also some glibc code

@peter.smith I find that in binutils-gdb, the AArch64 option is named `-z force-bti`, not `--force-bti` (commit `[BFD, LD, AArch64, 2/3] Add --force-bti to enable BTI and to select BTI enabled PLTs`). Do you intend to make them consistent?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D59780/new/

https://reviews.llvm.org/D59780