Messages in this thread | | | Date | Wed, 27 Oct 2021 14:46:49 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 00/15] x86: Add support for Clang CFI |
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On Wed, Oct 27, 2021 at 01:05:15PM +0100, Mark Rutland wrote: > On Tue, Oct 26, 2021 at 10:16:22PM +0200, Peter Zijlstra wrote: > > On Wed, Oct 13, 2021 at 11:16:43AM -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 > > > > So, if I understand this right, the compiler emits, for every function > > two things: 1) the actual funcion and 2) a jump-table entry. > > > > Then, every time the address of a function is taken, 2) is given instead > > of the expected 1), right? > > Yes, and we had to bodge around this with function_nocfi() to get the > actual function address.
The patch set under consideration seems to have forgotten to provide one for x86 :/
> Really there should be a compiler intrinsic or attribute for this, given > the compiler has all the releveant information available. On arm64 we > had to us inine asm to generate the addres...
Agreed, this *really* shouldn't be an arch asm hack trying to undo something the compiler did.
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