CVE-2024-56761— Linux kernel 安全漏洞

x86/fred: Clear WFE in missing-ENDBRANCH #CPs

In the Linux kernel, the following vulnerability has been resolved: x86/fred: Clear WFE in missing-ENDBRANCH #CPs An indirect branch instruction sets the CPU indirect branch tracker (IBT) into WAIT_FOR_ENDBRANCH (WFE) state and WFE stays asserted across the instruction boundary. When the decoder finds an inappropriate instruction while WFE is set ENDBR, the CPU raises a #CP fault. For the "kernel IBT no ENDBR" selftest where #CPs are deliberately triggered, the WFE state of the interrupted context needs to be cleared to let execution continue. Otherwise when the CPU resumes from the instruction that just caused the previous #CP, another missing-ENDBRANCH #CP is raised and the CPU enters a dead loop. This is not a problem with IDT because it doesn't preserve WFE and IRET doesn't set WFE. But FRED provides space on the entry stack (in an expanded CS area) to save and restore the WFE state, thus the WFE state is no longer clobbered, so software must clear it. Clear WFE to avoid dead looping in ibt_clear_fred_wfe() and the !ibt_fatal code path when execution is allowed to continue. Clobbering WFE in any other circumstance is a security-relevant bug. [ dhansen: changelog rewording ]

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于在x86/fred模块中，当触发“kernel IBT no ENDBR”自测试时，#CP中断后，中断上下文的WFE状态未被清除，导致CPU在恢复执行时再次引发missing-ENDBRANCH #CP，进入死循环，影响系统的正常运行和安全性。

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