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79 lines
2.9 KiB
Diff
79 lines
2.9 KiB
Diff
https://github.com/google/woff2/commit/23a34adec39d7cef30c1eebbf775a1ea5cc43c53
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From 23a34adec39d7cef30c1eebbf775a1ea5cc43c53 Mon Sep 17 00:00:00 2001
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From: David Benjamin <davidben@google.com>
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Date: Thu, 26 Oct 2023 10:16:05 -0400
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Subject: [PATCH] Fix undefined type-punning when loading/storing words
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Despite common practice, type-punning integer types out of buffers is
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undefined in C and C++. It's both a strict aliasing violation on access,
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and if the pointer isn't aligned, an alignment violation on cast. Being
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undefined, the compiler is allowed to arbitrarily miscompile the code
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when we rely on it.
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Instead, the two legal ways to pull a uint32_t out of a buffer are to
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either use memcpy, or load byte by byte and use shifts. In both cases,
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a good compiler should be smart enough to recognize what we're doing and
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generate reasonable code. Since there was already fallback code for the
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latter (for a middle-endian architecture?), I went ahead and switched to
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that.
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This change is needed to fix UBSan violations in Chromium.
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--- a/src/store_bytes.h
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+++ b/src/store_bytes.h
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@@ -27,15 +27,8 @@ inline size_t StoreU32(uint8_t* dst, size_t offset, uint32_t x) {
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}
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inline size_t Store16(uint8_t* dst, size_t offset, int x) {
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-#if defined(WOFF_LITTLE_ENDIAN)
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- *reinterpret_cast<uint16_t*>(dst + offset) =
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- ((x & 0xFF) << 8) | ((x & 0xFF00) >> 8);
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-#elif defined(WOFF_BIG_ENDIAN)
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- *reinterpret_cast<uint16_t*>(dst + offset) = static_cast<uint16_t>(x);
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-#else
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dst[offset] = x >> 8;
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dst[offset + 1] = x;
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-#endif
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return offset + 2;
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}
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@@ -47,17 +40,8 @@ inline void StoreU32(uint32_t val, size_t* offset, uint8_t* dst) {
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}
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inline void Store16(int val, size_t* offset, uint8_t* dst) {
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-#if defined(WOFF_LITTLE_ENDIAN)
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- *reinterpret_cast<uint16_t*>(dst + *offset) =
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- ((val & 0xFF) << 8) | ((val & 0xFF00) >> 8);
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- *offset += 2;
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-#elif defined(WOFF_BIG_ENDIAN)
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- *reinterpret_cast<uint16_t*>(dst + *offset) = static_cast<uint16_t>(val);
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- *offset += 2;
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-#else
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dst[(*offset)++] = val >> 8;
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dst[(*offset)++] = val;
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-#endif
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}
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inline void StoreBytes(const uint8_t* data, size_t len,
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--- a/src/woff2_common.cc
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+++ b/src/woff2_common.cc
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@@ -19,16 +19,8 @@ uint32_t ComputeULongSum(const uint8_t* buf, size_t size) {
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uint32_t checksum = 0;
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size_t aligned_size = size & ~3;
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for (size_t i = 0; i < aligned_size; i += 4) {
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-#if defined(WOFF_LITTLE_ENDIAN)
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- uint32_t v = *reinterpret_cast<const uint32_t*>(buf + i);
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- checksum += (((v & 0xFF) << 24) | ((v & 0xFF00) << 8) |
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- ((v & 0xFF0000) >> 8) | ((v & 0xFF000000) >> 24));
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-#elif defined(WOFF_BIG_ENDIAN)
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- checksum += *reinterpret_cast<const uint32_t*>(buf + i);
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-#else
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- checksum += (buf[i] << 24) | (buf[i + 1] << 16) |
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- (buf[i + 2] << 8) | buf[i + 3];
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-#endif
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+ checksum +=
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+ (buf[i] << 24) | (buf[i + 1] << 16) | (buf[i + 2] << 8) | buf[i + 3];
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}
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// treat size not aligned on 4 as if it were padded to 4 with 0's
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