To identify the risk factors associated with unplanned admission after day-case haemorrhoidectomy... more To identify the risk factors associated with unplanned admission after day-case haemorrhoidectomy. METHODS: This was a retrospective review of the outcomes of patients who underwent elective, intended day-case haemorrhoidectomy in a surgical institution between January 2005 and December 2009. Data were generated from a computerized database. Information on patient demographics, type of surgery, mode of anaesthesia, operative time, operation end time, and perioperative drugs were collected and analysed. Unplanned admission was carefully recorded. RESULTS: In a 5-year period, 243 patients underwent intended day-case haemorrhoidectomy. Of these, 43 (17.7%) had unplanned admission, with acute urinary retention as the most common cause (n = 30). Using univariate analysis, male gender, the use of spinal anaesthesia, and a late operation end time of after 2 PM were found to be positive risk factors associated with unplanned admission, whereas the use of single-dose dexamethasone during induction was identified as having a negative effect on unplanned admission. However, multivariate analysis showed that only male gender, the use of spinal anaesthesia, and a late operation end time of after 2 PM were independent risk factors. CONCLUSION: Good operation listing and the use of general anaesthesia are recommended in the practice of day-case haemorrhoidectomy.
Operating system (OS) kernels such as Windows, Linux, and MacOS are vulnerable to control-flow hi... more Operating system (OS) kernels such as Windows, Linux, and MacOS are vulnerable to control-flow hijacking. Defenses exist, but many require efficient intra-address space isolation. For example, execute-only memory requires read protection of code segments, and shadow stacks require write protection from buffer overwrites. Intel's Protection Keys for Userspace (PKU) could, in principle, provide the intra-kernel isolation needed to implement such features, but, when used as designed, it applies only to user-mode application code. This paper presents an unconventional approach to memory protection, allowing PKU to be used within the OS kernel on existing Intel hardware, replacing the traditional user/kernel isolation mechanism and, simultaneously, enabling efficient intrakernel isolation. We call the resulting mechanism Protection Keys for Kernelspace (PKK). To demonstrate its utility and efficiency, we present a system we call IskiOS: a Linux variant featuring execute-only memory (XOM) and the first-ever race-free shadow stacks for x86-64. Experiments with the LMBench kernel microbenchmarks display an average overhead of about 11% for PKK and no additional overhead for XOM. IskiOS's shadow stacks bring the total to 22%. For full applications, experiments with the system benchmarks of the Phoronix test suite display negligible overhead for PKK and XOM, and less than 5% for shadow stacks. 1 "IskiOS" means "shadow" in Greek.
To identify the risk factors associated with unplanned admission after day-case haemorrhoidectomy... more To identify the risk factors associated with unplanned admission after day-case haemorrhoidectomy. METHODS: This was a retrospective review of the outcomes of patients who underwent elective, intended day-case haemorrhoidectomy in a surgical institution between January 2005 and December 2009. Data were generated from a computerized database. Information on patient demographics, type of surgery, mode of anaesthesia, operative time, operation end time, and perioperative drugs were collected and analysed. Unplanned admission was carefully recorded. RESULTS: In a 5-year period, 243 patients underwent intended day-case haemorrhoidectomy. Of these, 43 (17.7%) had unplanned admission, with acute urinary retention as the most common cause (n = 30). Using univariate analysis, male gender, the use of spinal anaesthesia, and a late operation end time of after 2 PM were found to be positive risk factors associated with unplanned admission, whereas the use of single-dose dexamethasone during induction was identified as having a negative effect on unplanned admission. However, multivariate analysis showed that only male gender, the use of spinal anaesthesia, and a late operation end time of after 2 PM were independent risk factors. CONCLUSION: Good operation listing and the use of general anaesthesia are recommended in the practice of day-case haemorrhoidectomy.
Operating system (OS) kernels such as Windows, Linux, and MacOS are vulnerable to control-flow hi... more Operating system (OS) kernels such as Windows, Linux, and MacOS are vulnerable to control-flow hijacking. Defenses exist, but many require efficient intra-address space isolation. For example, execute-only memory requires read protection of code segments, and shadow stacks require write protection from buffer overwrites. Intel's Protection Keys for Userspace (PKU) could, in principle, provide the intra-kernel isolation needed to implement such features, but, when used as designed, it applies only to user-mode application code. This paper presents an unconventional approach to memory protection, allowing PKU to be used within the OS kernel on existing Intel hardware, replacing the traditional user/kernel isolation mechanism and, simultaneously, enabling efficient intrakernel isolation. We call the resulting mechanism Protection Keys for Kernelspace (PKK). To demonstrate its utility and efficiency, we present a system we call IskiOS: a Linux variant featuring execute-only memory (XOM) and the first-ever race-free shadow stacks for x86-64. Experiments with the LMBench kernel microbenchmarks display an average overhead of about 11% for PKK and no additional overhead for XOM. IskiOS's shadow stacks bring the total to 22%. For full applications, experiments with the system benchmarks of the Phoronix test suite display negligible overhead for PKK and XOM, and less than 5% for shadow stacks. 1 "IskiOS" means "shadow" in Greek.
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Papers by Pik Yan Chan