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mte: add comment about the reserved slab canary value

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Dmitry Muhomor 2023-10-29 15:36:37 +02:00 committed by Daniel Micay
parent f16ef601d4
commit 7a6dbd8152
1 changed files with 5 additions and 1 deletions
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6
h_malloc.c
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@ -491,7 +491,11 @@ static void set_slab_canary_value(UNUSED struct slab_metadata *metadata, UNUSED
metadata->canary_value = get_random_u64(rng) & canary_mask;
#ifdef HAS_ARM_MTE
if (unlikely(metadata->canary_value == 0)) {
metadata->canary_value = 0x100;
// 0 is reserved to support disabling MTE at runtime (this is required on Android).
// When MTE is enabled, writing and reading of canaries is disabled, i.e. canary remains zeroed.
// After MTE is disabled, canaries that are set to 0 are ignored, since they wouldn't match
// slab's metadata->canary_value.
metadata->canary_value = 0x100; // 0x100 was chosen as the smallest acceptable value
}
#endif
#endif