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Microcode checksum verification should be done using unsigned 32-bit values otherwise the calculation overflow results in undefined behaviour. This is also nicely documented in the SDM, section "Microcode Update Checksum": "To check for a corrupt microcode update, software must perform a unsigned DWORD (32-bit) checksum of the microcode update. Even though some fields are signed, the checksum procedure treats all DWORDs as unsigned. Microcode updates with a header version equal to 00000001H must sum all DWORDs that comprise the microcode update. A valid checksum check will yield a value of 00000000H." but for some reason the code has been using ints from the very beginning. In practice, this bug possibly manifested itself only when doing the microcode data checksum - apparently, currently shipped Intel microcode doesn't have an extended signature table for which we do checksum verification too. UBSAN: Undefined behaviour in arch/x86/kernel/cpu/microcode/intel_lib.c:105:12 signed integer overflow: -1500151068 + -2125470173 cannot be represented in type 'int' CPU: 0 PID: 0 Comm: swapper Not tainted 4.5.0-rc5+ #495 ... Call Trace: dump_stack ? inotify_ioctl ubsan_epilogue handle_overflow __ubsan_handle_add_overflow microcode_sanity_check get_matching_model_microcode.isra.2.constprop.8 ? early_idt_handler_common ? strlcpy ? find_cpio_data load_ucode_intel_bsp load_ucode_bsp ? load_ucode_bsp x86_64_start_kernel [ Expand and massage commit message. ] Signed-off-by: Chris Bainbridge <chris.bainbridge@gmail.com> Signed-off-by: Borislav Petkov <bp@suse.de> Cc: hmh@hmh.eng.br Link: http://lkml.kernel.org/r/1456834359-5132-1-git-send-email-chris.bainbridge@gmail.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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| entry | ||
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| kvm | ||
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| lib | ||
| math-emu | ||
| mm | ||
| net | ||
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| xen | ||
| .gitignore | ||
| Kbuild | ||
| Kconfig | ||
| Kconfig.cpu | ||
| Kconfig.debug | ||
| Makefile | ||
| Makefile_32.cpu | ||
| Makefile.um | ||