Add character devices that expose PAPR-specific system parameters and VPD to user space.
The problem: important platform features are enabled on Linux VMs through the powerpc-specific rtas() syscall in combination with writeable mappings of /dev/mem. In typical usage, this is encapsulated behind APIs provided by the librtas library. This paradigm is incompatible with lockdown, which prohibits /dev/mem access. It also is too low-level in many cases: a single logical operation may require multiple sys_rtas() calls in succession to complete. This carries the risk that a process may exit while leaving an operation unfinished. It also means that callers must coordinate their use of the syscall for functions that cannot tolerate multiple concurrent clients, such as ibm,get-vpd. The solution presented here is to add a pair of small pseries-specific "drivers," one for VPD and one for system parameters. The new drivers expose these facilities to user space in ways that are compatible with lockdown and require no coordination between their clients. Both drivers could potentially support poll() methods to notify clients of changes to parameters or VPD that happen due to partition migration and other events. But that should be safe to leave for later, assuming there's any interest. I have made changes to librtas to prefer the new interfaces and verified that existing clients work correctly with the new code. A draft PR for that work is here: https://github.com/ibm-power-utilities/librtas/pull/36 I expect to propose at least one more small driver in this style for platform dump retrieval in a separate submission in the future. I consider the work in this series mature enough now to request review for inclusion as-is. --- Changes in v1 vs initial RFC: - Add papr-sysparm driver and tests. - Add a papr-miscdev.h uapi header. - Prevent sys_rtas() from interfering with papr-vpd call sequences. - Handle -4 ("VPD changed") status in papr-vpd. - Include string_helpers.h in papr-vpd.c, per Michal Suchánek - Link to RFC: https://lore.kernel.org/r/20230822-papr-sys_rtas-vs-lockdown-v1-0-932623cf3...@linux.ibm.com --- Nathan Lynch (7): powerpc/uapi: export papr-miscdev.h header powerpc/pseries: papr-vpd char driver for VPD retrieval powerpc/rtas: serialize ibm,get-vpd service with papr-vpd sequences powerpc/pseries/papr-sysparm: validate buffer object lengths powerpc/pseries/papr-sysparm: expose chardev API to user space powerpc/selftests: add test for papr-vpd powerpc/selftests: add test for papr-sysparm Documentation/userspace-api/ioctl/ioctl-number.rst | 4 + arch/powerpc/include/asm/papr-sysparm.h | 17 +- arch/powerpc/include/asm/papr-vpd.h | 18 + arch/powerpc/include/uapi/asm/papr-miscdev.h | 9 + arch/powerpc/include/uapi/asm/papr-sysparm.h | 58 +++ arch/powerpc/include/uapi/asm/papr-vpd.h | 22 + arch/powerpc/kernel/rtas.c | 26 + arch/powerpc/platforms/pseries/Makefile | 1 + arch/powerpc/platforms/pseries/papr-sysparm.c | 207 +++++++- arch/powerpc/platforms/pseries/papr-vpd.c | 542 +++++++++++++++++++++ tools/testing/selftests/powerpc/Makefile | 2 + .../selftests/powerpc/papr_sysparm/.gitignore | 1 + .../selftests/powerpc/papr_sysparm/Makefile | 12 + .../selftests/powerpc/papr_sysparm/papr_sysparm.c | 164 +++++++ .../testing/selftests/powerpc/papr_vpd/.gitignore | 1 + tools/testing/selftests/powerpc/papr_vpd/Makefile | 12 + .../testing/selftests/powerpc/papr_vpd/papr_vpd.c | 352 +++++++++++++ 17 files changed, 1440 insertions(+), 8 deletions(-) --- base-commit: eddc90ea2af5933249ea1a78119f2c8ef8d07156 change-id: 20230817-papr-sys_rtas-vs-lockdown-5c54505db792 Best regards, -- Nathan Lynch <nath...@linux.ibm.com>
