This is v5 of Syscall User Dispatch. It has some big changes in comparison to v4.
First of all, it allows the vdso trampoline code for architectures that support it. This is exposed through an arch hook. It also addresses the concern about what happens when a bad selector is provided, instead of SIGSEGV, we fail with SIGSYS, which is more debug-able.
Another major change is that it is now based on top of Gleixner's common syscall entry work, and is supposed to only be used by that code. Therefore, the entry symbol is not exported outside of kernel/entry/ code.
The biggest change in this version is the attempt to avoid using one of the final TIF flags on x86 32 bit, without increasing the size of that variable to 64 bit. My expectation is that, with this work, plus the removal of TIF_IA32, TIF_X32 and TIF_FORCE_TF, we might be able to avoid changing this field to 64 bits at all. Instead, this follows the suggestion by Andy to have a generic TIF flag for SECCOMP and this mechanism, and use another field to decide which one is enabled. The code for this is not complex, so it seems like a viable approach.
Finally, this version adds some documentation to the feature.
Kees, I dropped your reviewed-by on patch 5, given the amount of changes.
Thanks,
Previous submissions are archived at: RFC/v1: https://lkml.org/lkml/2020/7/8/96 v2: https://lkml.org/lkml/2020/7/9/17 v3: https://lkml.org/lkml/2020/7/12/4 v4: https://lwn.net/ml/linux-kernel/20200712044516.2347844-1-krisman@collabora.c...
Gabriel Krisman Bertazi (9): kernel: Support TIF_SYSCALL_INTERCEPT flag kernel: entry: Support TIF_SYSCAL_INTERCEPT on common entry code x86: vdso: Expose sigreturn address on vdso to the kernel signal: Expose SYS_USER_DISPATCH si_code type kernel: Implement selective syscall userspace redirection kernel: entry: Support Syscall User Dispatch for common syscall entry x86: Enable Syscall User Dispatch selftests: Add kselftest for syscall user dispatch doc: Document Syscall User Dispatch
.../admin-guide/syscall-user-dispatch.rst | 87 ++++++ arch/Kconfig | 21 ++ arch/x86/Kconfig | 1 + arch/x86/entry/vdso/vdso2c.c | 2 + arch/x86/entry/vdso/vdso32/sigreturn.S | 2 + arch/x86/entry/vdso/vma.c | 15 + arch/x86/include/asm/elf.h | 1 + arch/x86/include/asm/thread_info.h | 4 +- arch/x86/include/asm/vdso.h | 2 + arch/x86/kernel/signal_compat.c | 2 +- fs/exec.c | 8 + include/linux/entry-common.h | 6 +- include/linux/sched.h | 8 +- include/linux/seccomp.h | 20 +- include/linux/syscall_intercept.h | 71 +++++ include/linux/syscall_user_dispatch.h | 29 ++ include/uapi/asm-generic/siginfo.h | 3 +- include/uapi/linux/prctl.h | 5 + kernel/entry/Makefile | 1 + kernel/entry/common.c | 32 +- kernel/entry/common.h | 15 + kernel/entry/syscall_user_dispatch.c | 101 ++++++ kernel/fork.c | 10 +- kernel/seccomp.c | 7 +- kernel/sys.c | 5 + tools/testing/selftests/Makefile | 1 + .../syscall_user_dispatch/.gitignore | 2 + .../selftests/syscall_user_dispatch/Makefile | 9 + .../selftests/syscall_user_dispatch/config | 1 + .../syscall_user_dispatch.c | 292 ++++++++++++++++++ 30 files changed, 744 insertions(+), 19 deletions(-) create mode 100644 Documentation/admin-guide/syscall-user-dispatch.rst create mode 100644 include/linux/syscall_intercept.h create mode 100644 include/linux/syscall_user_dispatch.h create mode 100644 kernel/entry/common.h create mode 100644 kernel/entry/syscall_user_dispatch.c create mode 100644 tools/testing/selftests/syscall_user_dispatch/.gitignore create mode 100644 tools/testing/selftests/syscall_user_dispatch/Makefile create mode 100644 tools/testing/selftests/syscall_user_dispatch/config create mode 100644 tools/testing/selftests/syscall_user_dispatch/syscall_user_dispatch.c