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Linus Torvalds
caf12fa9c0
Pull x86 IBTI mitigation from Dave Hansen: "Mitigate Intra-mode Branch History Injection via classic BFP programs This adds the branch history clearing mitigation to cBPF programs for x86. Intra-mode BHI attacks via cBPF a.k.a IBTI-History was reported by researchers at VUSec. For hardware that doesn't support BHI_DIS_S, the recommended mitigation is to run the short software sequence followed by the IBHF instruction after cBPF execution. On hardware that does support BHI_DIS_S, enable BHI_DIS_S and execute the IBHF after cBPF execution. The Indirect Branch History Fence (IBHF) is a new instruction that prevents indirect branch target predictions after the barrier from using branch history from before the barrier while BHI_DIS_S is enabled. On older systems this will map to a NOP. It is recommended to add this fence at the end of the cBPF program to support VM migration. This instruction is required on newer parts with BHI_NO to fully mitigate against these attacks. The current code disables the mitigation for anything running with the SYS_ADMIN capability bit set. The intention was not to waste time mitigating a process that has access to anything it wants anyway" * tag 'ibti-hisory-for-linus-2025-05-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/bhi: Do not set BHI_DIS_S in 32-bit mode x86/bpf: Add IBHF call at end of classic BPF x86/bpf: Call branch history clearing sequence on exit
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.