fixup_umip_exception(9)

💅 fixup_umip_exception — the Kernel API Manual, bestie edition ✨

okay so real talk, this page lives in the Kernel API Manual and it's about one very specific little hero function. let me tell you everything, no gatekeeping 💖

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✨ NAME ✨

fixup_umip_exception — the function that fixes up a general protection fault caused by UMIP 🫶

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🌸 SYNOPSIS 🌸

bool fixup_umip_exception (struct pt_regs *regs );

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🎀 ARGUMENTS 🎀

• regs — the registers as saved when entering the #GP handler. like, the whole little snapshot of what was going on at the moment of the oops 💅

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🦋 DESCRIPTION 🦋

ok so picture this: the instructions SGDT, SIDT, STR, SMSW and SLDT cause a general protection fault if they're executed with CPL > 0 — yep, that means from user space 😭 so this function rolls up and fixes the exception up 😌 and it provides dummy results for SGDT, SIDT and SMSW. but bestie, listen — STR and SLDT are not fixed up. not them. they get nothing. 💀

now for the actual mechanics, because the way this works is kind of iconic:

• if the operands are memory addresses 🧚 the results get copied to user-space memory as indicated by the instruction pointed by eIP, using the registers indicated in the instruction operands ✨
• if the operands are registers 🎀 the results get copied into the context that was saved when entering kernel mode 💜

and the return value, the main character of it all: true if emulation was successful; false if not. periodt. 👑

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🌈 SEE ALSO 🌈

• Kernel file ./arch/x86/kernel/umip.c
• umip_printk(9)
• identify_insn(9)
• emulate_umip_insn(9)
• force_sig_info_umip_fault(9)

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🍓 quick vibe check: those STR and SLDT instructions staying un-fixed-up is not a bug note, it's just the actual behaviour, so don't come for me 🙈

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and that's the whole page, bestie!! shoutout to the source tree at ./arch/x86/kernel and the October 2026 date — they ate and left absolutely no crumbs 💅✨👑