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Signed-off-by: Cui Wei --- .../translations/zh_CN/staging/index.rst | 2 +- .../zh_CN/staging/speculation.rst | 85 +++++++++++++++++++ 2 files changed, 86 insertions(+), 1 deletion(-) create mode 100644 Documentation/translations/zh_CN/staging/speculation.rst diff --git a/Documentation/translations/zh_CN/staging/index.rst b/Documentation/translations/zh_CN/staging/index.rst index bb55c81c84a3..6d68fabce175 100644 --- a/Documentation/translations/zh_CN/staging/index.rst +++ b/Documentation/translations/zh_CN/staging/index.rst @@ -13,6 +13,7 @@ .. toctree:: :maxdepth: 2 + speculation xz TODOList: @@ -21,6 +22,5 @@ TODOList: * lzo * remoteproc * rpmsg -* speculation * static-keys * tee diff --git a/Documentation/translations/zh_CN/staging/speculation.rst b/Documentation/translations/zh_CN/staging/speculation.rst new file mode 100644 index 000000000000..c36d33f67897 --- /dev/null +++ b/Documentation/translations/zh_CN/staging/speculation.rst @@ -0,0 +1,85 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: ../disclaimer-zh_CN.rst + +:Original: Documentation/staging/speculation.rst + +:翻译: + + 崔巍 Cui Wei + +======== +推测执行 +======== + +本文档解释了推测执行的潜在影响，以及如何使用通用API来减轻不良影响。 + +------------------------------------------------------------------------------ + +为提高性能并减少平均延迟，许多现代处理器都采用分支预测等推测执行技术，执行结果 +可能在后续阶段被丢弃。 + +通常情况下，我们无法从架构状态（如寄存器内容）观察到推测执行。然而，在某些情况 +下从微架构状态观察其影响是可能的，例如数据是否存在于缓存中。这种状态可能会形成 +侧信道，通过观察侧信道可以提取秘密信息。 + +例如，在分支预测存在的情况下，边界检查可能被推测执行的代码忽略。考虑以下代码:: + + int load_array(int *array, unsigned int index) + { + if (index >= MAX_ARRAY_ELEMS) + return 0; + else + return array[index]; + } + +在arm64上，可以编译成如下汇编序列:: + + CMP , #MAX_ARRAY_ELEMS + B.LT less + MOV , #0 + RET + less: + LDR , [, ] + RET + +处理器有可能误预测条件分支，并推测性装载array[index]，即使index >= MAX_ARRAY_ELEMS。 +这个值随后会被丢弃，但推测的装载可能会影响微架构状态，随后可被测量到。 + +涉及多个依赖内存访问的更复杂序列可能会导致敏感信息泄露。以前面的示例为基础，考虑 +以下代码:: + + int load_dependent_arrays(int *arr1, int *arr2, int index) + { + int val1, val2, + + val1 = load_array(arr1, index); + val2 = load_array(arr2, val1); + + return val2; + } + +根据推测，对load_array()的第一次调用可能会返回一个越界地址的值，而第二次调用将影响 +依赖于该值的微架构状态。这可能会提供一个任意读取原语。 + +缓解推测执行侧信道 +================== + +内核提供了一个通用API以确保即使在推测情况下也能遵守边界检查。受推测执行侧信道影响 +的架构应当实现这些原语。 + +中的array_index_nospec()辅助函数可用于防止信息通过侧信道泄漏。 + +调用array_index_nospec(index, size)将返回一个经过净化的索引值，即使在CPU推测执行 +条件下，该值也会被严格限制在[0, size)范围内。 + +这可以用来保护前面的load_array()示例:: + + int load_array(int *array, unsigned int index) + { + if (index >= MAX_ARRAY_ELEMS) + return 0; + else { + index = array_index_nospec(index, MAX_ARRAY_ELEMS); + return array[index]; + } + } -- 2.43.0