v2: - Added the missing "--from" during patch generation. - Added missing patch to 6.1 backport.
This is a backport of mitigation for Indirect Target Selection (ITS).
ITS is a bug in some Intel CPUs that affects indirect branches including RETs in the first half of a cacheline. Mitigation is to relocate the affected branches to an ITS-safe thunk.
Below additional upstream commits are required to cover some of the special cases like indirects in asm and returns in static calls:
cfceff8526a4 ("x86/speculation: Simplify and make CALL_NOSPEC consistent") 052040e34c08 ("x86/speculation: Add a conditional CS prefix to CALL_NOSPEC") c8c81458863a ("x86/speculation: Remove the extra #ifdef around CALL_NOSPEC") d2408e043e72 ("x86/alternative: Optimize returns patching") 4ba89dd6ddec ("x86/alternatives: Remove faulty optimization")
[1] https://github.com/torvalds/linux/commit/6f5bf947bab06f37ff931c359fd5770c4d9...
--- Borislav Petkov (AMD) (1): x86/alternative: Optimize returns patching
Josh Poimboeuf (1): x86/alternatives: Remove faulty optimization
Pawan Gupta (10): x86/speculation: Simplify and make CALL_NOSPEC consistent x86/speculation: Add a conditional CS prefix to CALL_NOSPEC x86/speculation: Remove the extra #ifdef around CALL_NOSPEC Documentation: x86/bugs/its: Add ITS documentation x86/its: Enumerate Indirect Target Selection (ITS) bug x86/its: Add support for ITS-safe indirect thunk x86/its: Add support for ITS-safe return thunk x86/its: Enable Indirect Target Selection mitigation x86/its: Add "vmexit" option to skip mitigation on some CPUs x86/its: Align RETs in BHB clear sequence to avoid thunking
Peter Zijlstra (2): x86,nospec: Simplify {JMP,CALL}_NOSPEC x86/its: Use dynamic thunks for indirect branches
Documentation/ABI/testing/sysfs-devices-system-cpu | 1 + Documentation/admin-guide/hw-vuln/index.rst | 1 + .../hw-vuln/indirect-target-selection.rst | 156 ++++++++++++++ Documentation/admin-guide/kernel-parameters.txt | 15 ++ arch/x86/Kconfig | 11 + arch/x86/entry/entry_64.S | 20 +- arch/x86/include/asm/alternative.h | 24 +++ arch/x86/include/asm/cpufeatures.h | 3 + arch/x86/include/asm/msr-index.h | 8 + arch/x86/include/asm/nospec-branch.h | 57 ++++-- arch/x86/kernel/alternative.c | 226 ++++++++++++++++++++- arch/x86/kernel/cpu/bugs.c | 139 ++++++++++++- arch/x86/kernel/cpu/common.c | 63 ++++-- arch/x86/kernel/ftrace.c | 2 +- arch/x86/kernel/module.c | 7 + arch/x86/kernel/static_call.c | 2 +- arch/x86/kernel/vmlinux.lds.S | 10 + arch/x86/kvm/x86.c | 4 +- arch/x86/lib/retpoline.S | 39 ++++ arch/x86/net/bpf_jit_comp.c | 8 +- drivers/base/cpu.c | 8 + include/linux/cpu.h | 2 + include/linux/module.h | 5 + 23 files changed, 768 insertions(+), 43 deletions(-) --- change-id: 20250512-its-5-15-0e0385221e32