65 lines
2.1 KiB
Diff
65 lines
2.1 KiB
Diff
From 53b0cfde580e86b03d0d27a488b6c134f662e957 Mon Sep 17 00:00:00 2001
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From: Jack Lloyd <jack@randombit.net>
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Date: Sat, 19 Oct 2024 07:43:18 -0400
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Subject: [PATCH] Add more value barriers to avoid compiler induced side
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channels
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The paper https://arxiv.org/pdf/2410.13489 claims that on specific
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architectures Clang and GCC may introduce jumps here. The donna128
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issues only affect 32-bit processors, which explains why we would not
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see it in the x86-64 valgrind runs.
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The GHASH leak would seem to be generic but the authors only observed
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it on RISC-V.
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---
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src/lib/utils/donna128.h | 5 +++--
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src/lib/utils/ghash/ghash.cpp | 2 +-
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2 files changed, 4 insertions(+), 3 deletions(-)
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diff --git a/src/lib/utils/donna128.h b/src/lib/utils/donna128.h
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index ff57190..1cbf060 100644
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--- a/src/lib/utils/donna128.h
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+++ b/src/lib/utils/donna128.h
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@@ -8,6 +8,7 @@
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#ifndef BOTAN_CURVE25519_DONNA128_H_
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#define BOTAN_CURVE25519_DONNA128_H_
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+#include <botan/internal/ct_utils.h>
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#include <botan/mul128.h>
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namespace Botan {
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@@ -61,7 +62,7 @@ class donna128 final
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l += x.l;
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h += x.h;
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- const uint64_t carry = (l < x.l);
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+ const uint64_t carry = CT::Mask<uint64_t>::is_lt(l, x.l).if_set_return(1);
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h += carry;
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return *this;
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}
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@@ -69,7 +70,7 @@ class donna128 final
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donna128& operator+=(uint64_t x)
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{
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l += x;
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- const uint64_t carry = (l < x);
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+ const uint64_t carry = CT::Mask<uint64_t>::is_lt(l, x).if_set_return(1);
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h += carry;
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return *this;
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}
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diff --git a/src/lib/utils/ghash/ghash.cpp b/src/lib/utils/ghash/ghash.cpp
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index e24f5e0..8f0afa7 100644
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--- a/src/lib/utils/ghash/ghash.cpp
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+++ b/src/lib/utils/ghash/ghash.cpp
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@@ -139,7 +139,7 @@ void GHASH::key_schedule(const uint8_t key[], size_t length)
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m_HM[4*j+2*i+1] = H1;
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// GCM's bit ops are reversed so we carry out of the bottom
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- const uint64_t carry = R * (H1 & 1);
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+ const uint64_t carry = CT::Mask<uint64_t>::expand(H1 & 1).if_set_return(R);
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H1 = (H1 >> 1) | (H0 << 63);
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H0 = (H0 >> 1) ^ carry;
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}
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--
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2.33.0
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