From: Benjamin Berg <benja...@sipsolutions.net> Currently UML uses ptrace in order to implement userspace processes. This works really well, however, it requires six context switches per pagefault (get faultinfo, run syscalls, continue process).
By switching to use SECCOMP, the whole process becomes more collaborative as the userspace process can run code, including host syscalls, before jumping into the kernel and after the kernel returns control. This means pagefaults only require two context switches to be processed. In pagefault heavy scenarios (e.g. fork/exec) the performance increase of doing this can be considerable, with runtimes dropping by 30% or more. Note that the current syscall filter can easily be abused by a userspace process to execute arbitrary host syscalls. I think it is possible to efficiently detect such attempts and kill the offending processes by (ab)using the rt_sigaction syscall in order to set/get a flag that userspace code cannot tamper with. v2: * Fixed FP register store/restore * Plenty of other fixes and improvements Benjamin Berg (28): um: Switch printk calls to adhere to correct coding style um: Declare fix_range_common as a static function um: Drop support for hosts without SYSEMU_SINGLESTEP support um: Drop NULL check from start_userspace um: Make errors to stop ptraced child fatal during startup um: Don't use vfprintf() for os_info() um: Do not use printk in SIGWINCH helper thread um: Reap winch thread if it fails um: Do not use printk in userspace trampoline um: Always inline stub functions um: Rely on PTRACE_SETREGSET to set FS/GS base registers um: Remove unused register save/restore functions um: Mark 32bit syscall helpers as clobbering memory um: Remove stub-data.h include from common-offsets.h um: Create signal stack memory assignment in stub_data um: Add generic stub_syscall6 function um: Rework syscall handling um: Store full CSGSFS and SS register from mcontext um: Pass full mm_id to functions creating helper processes um: Move faultinfo extraction into userspace routine um: Use struct uml_pt_regs for copy_context_skas0 um: Add UML_SECCOMP configuration option um: Add stub side of SECCOMP/futex based process handling um: Add helper functions to get/set state for SECCOMP um: Add SECCOMP support detection and initialization um: Die if a child dies unexpectedly in seccomp mode um: Implement kernel side of SECCOMP based process handling um: Delay flushing syscalls until the thread is restarted arch/um/Kconfig | 19 + arch/um/drivers/chan_user.c | 42 +- arch/um/drivers/line.c | 13 +- arch/um/include/asm/processor-generic.h | 1 - arch/um/include/shared/as-layout.h | 2 +- arch/um/include/shared/common-offsets.h | 14 +- arch/um/include/shared/kern_util.h | 3 +- arch/um/include/shared/os.h | 33 +- arch/um/include/shared/ptrace_user.h | 41 -- arch/um/include/shared/registers.h | 2 - arch/um/include/shared/skas/mm_id.h | 1 + arch/um/include/shared/skas/skas.h | 7 + arch/um/include/shared/skas/stub-data.h | 41 +- arch/um/include/shared/user.h | 8 + arch/um/kernel/exec.c | 10 +- arch/um/kernel/process.c | 12 +- arch/um/kernel/ptrace.c | 2 - arch/um/kernel/signal.c | 12 - arch/um/kernel/skas/Makefile | 4 +- arch/um/kernel/skas/clone.c | 33 +- arch/um/kernel/skas/mmu.c | 16 +- arch/um/kernel/skas/process.c | 8 + arch/um/kernel/skas/stub.c | 101 ++++ arch/um/kernel/tlb.c | 54 +- arch/um/os-Linux/process.c | 40 ++ arch/um/os-Linux/registers.c | 24 +- arch/um/os-Linux/signal.c | 7 + arch/um/os-Linux/skas/mem.c | 288 +++++---- arch/um/os-Linux/skas/process.c | 749 ++++++++++++++++-------- arch/um/os-Linux/start_up.c | 244 +++++--- arch/um/os-Linux/util.c | 19 +- arch/x86/um/Makefile | 2 +- arch/x86/um/asm/elf.h | 4 +- arch/x86/um/asm/processor_64.h | 3 - arch/x86/um/ldt.c | 47 +- arch/x86/um/os-Linux/Makefile | 1 - arch/x86/um/os-Linux/mcontext.c | 153 ++++- arch/x86/um/os-Linux/prctl.c | 12 - arch/x86/um/ptrace_32.c | 24 - arch/x86/um/ptrace_64.c | 26 - arch/x86/um/shared/sysdep/mcontext.h | 9 + arch/x86/um/shared/sysdep/ptrace_32.h | 4 - arch/x86/um/shared/sysdep/ptrace_user.h | 12 +- arch/x86/um/shared/sysdep/stub-data.h | 12 + arch/x86/um/shared/sysdep/stub.h | 4 + arch/x86/um/shared/sysdep/stub_32.h | 78 ++- arch/x86/um/shared/sysdep/stub_64.h | 57 +- arch/x86/um/stub_32.S | 56 -- arch/x86/um/stub_64.S | 50 -- arch/x86/um/syscalls_64.c | 62 +- arch/x86/um/tls_64.c | 2 +- 51 files changed, 1500 insertions(+), 968 deletions(-) create mode 100644 arch/um/kernel/skas/stub.c delete mode 100644 arch/x86/um/os-Linux/prctl.c create mode 100644 arch/x86/um/shared/sysdep/stub-data.h delete mode 100644 arch/x86/um/stub_32.S delete mode 100644 arch/x86/um/stub_64.S -- 2.38.1 _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um
