CVE-2024-56761
x86/fred: Clear WFE in missing-ENDBRANCH #CPs
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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 ]
Reserved 2024-12-29 | Published 2025-01-06 | Updated 2025-01-20 | Assigner Linuxgit.kernel.org/...c/151447859d6fb0dcce8259f0971c6e94fb801661
git.kernel.org/...c/b939f108e86b76119428a6fa4e92491e09ac7867
git.kernel.org/...c/dc81e556f2a017d681251ace21bf06c126d5a192
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