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Add more value barriers to avoid compiler induced side channels #4395

Merged
merged 3 commits into from
Oct 20, 2024
Merged

Add more value barriers to avoid compiler induced side channels #4395

merged 3 commits into from
Oct 20, 2024

Commits on Oct 20, 2024

  1. Add more value barriers to avoid compiler induced side channels 

    The paper https://arxiv.org/pdf/2410.13489 claims that on specific
architectures Clang and GCC may introduce jumps here. The donna128
issues only affect 32-bit processors, which explains why we would not
see it in the x86-64 valgrind runs.

The GHASH leak would seem to be generic but the authors only observed
it on RISC-V.
    @randombit
    randombit committed Oct 20, 2024
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  2. Add CT::value_barrier to donna conditional swap logic 

    No indications that Clang is currently converting this to conditional
jumps, but this construct seems prone to such problems.
    @randombit
    randombit committed Oct 20, 2024
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  3. Avoid another problematic construct in GHASH 

    There has been no indication that any compiler is converting this code
to assembly that uses conditional jumps, but it has the style of code
that would be vulnerable to Clang's range analysis optimizations.
    @randombit
    randombit committed Oct 20, 2024
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