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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/7/25 11:37, Edgecombe, Rick P wrote: >> /* >> * No point in checking CS -- the only way to get here is a user mode >> * trap to a high address, which means that we're in 64-bit user code. > I don't know. Is this as true any more? We are now sometimes guessing based on > regs->ip of a #GP. What if the kernel accidentally tries to jump to the vsyscall > address? Then we are reading the kernel stack and strange things. Maybe it's > worth replacing the comment with a check? Feel free to call this paranoid. The first check in emulate_vsyscall() is: /* Write faults or kernel-privilege faults never get fixed up. */ if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER) return false; If the kernel jumped to the vsyscall page, it would end up there, return false, and never reach the code near the "No point in checking CS" comment. Right? Or am I misunderstanding the scenario you're calling out? If I'm understanding it right, I'd be a bit reluctant to add a CS check as well.