Messages in this thread | | | From | Sami Tolvanen <> | Date | Tue, 5 Oct 2021 14:52:46 -0700 | Subject | Re: [PATCH v4 00/15] x86: Add support for Clang CFI |
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On Tue, Oct 5, 2021 at 1:37 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > On Thu, Sep 30, 2021 at 11:05:16AM -0700, Sami Tolvanen wrote: > > This series adds support for Clang's Control-Flow Integrity (CFI) > > checking to x86_64. With CFI, the compiler injects a runtime > > check before each indirect function call to ensure the target is > > a valid function with the correct static type. This restricts > > possible call targets and makes it more difficult for an attacker > > to exploit bugs that allow the modification of stored function > > pointers. For more details, see: > > > > https://clang.llvm.org/docs/ControlFlowIntegrity.html > > > > Note that v4 is based on tip/master. The first two patches contain > > objtool support for CFI, the remaining patches change function > > declarations to use opaque types, fix type mismatch issues that > > confuse the compiler, and disable CFI where it can't be used. > > > > You can also pull this series from > > > > https://github.com/samitolvanen/linux.git x86-cfi-v4 > > Does this work for indirect calls made from alternatives?
It works in the sense that indirect calls made from alternatives won't trip CFI. The compiler doesn't instrument inline assembly.
> I'm also wondering whether this works on CONFIG_RETPOLINE systems which > disable retpolines at runtime, combined with Peter's patch to use > objtool to replace retpoline thunk calls with indirect branches: > > 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls") > > Since presumably objtool runs after the CFI stuff is inserted.
The indirect call checking is before the retpoline thunk call, so replacing the call with an indirect call isn't a problem.
Sami
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