On Tue, Oct 31, 2023 at 03:46:02PM +0100, Anthony Harivel wrote: > Introduce a privileged helper to access RAPL MSR. > > The privileged helper tool, qemu-vmsr-helper, is designed to provide > virtual machines with the ability to read specific RAPL (Running Average > Power Limit) MSRs without requiring CAP_SYS_RAWIO privileges or relying > on external, out-of-tree patches. > > The helper tool leverages Unix permissions and SO_PEERCRED socket > options to enforce access control, ensuring that only processes > explicitly requesting read access via readmsr() from a valid Thread ID > can access these MSRs. > > The list of RAPL MSRs that are allowed to be read by the helper tool is > defined in rapl-msr-index.h. This list corresponds to the RAPL MSRs that > will be supported in the next commit titled "Add support for RAPL MSRs > in KVM/QEMU." > > Signed-off-by: Anthony Harivel <ahari...@redhat.com> > --- > docs/tools/index.rst | 1 + > docs/tools/qemu-vmsr-helper.rst | 89 ++++++ > meson.build | 5 + > tools/i386/qemu-vmsr-helper.c | 507 ++++++++++++++++++++++++++++++++ > tools/i386/rapl-msr-index.h | 28 ++ > 5 files changed, 630 insertions(+) > create mode 100644 docs/tools/qemu-vmsr-helper.rst > create mode 100644 tools/i386/qemu-vmsr-helper.c > create mode 100644 tools/i386/rapl-msr-index.h >
> +/* > + * Check if the TID that request the MSR read > + * belongs to the peer. It should a TID of a vCPU. > + */ > +static bool is_tid_present(pid_t pid, pid_t tid) > +{ > + char pidStr[20]; > + char tidStr[20]; > + > + snprintf(pidStr, sizeof(pidStr), "%d", pid); > + snprintf(tidStr, sizeof(tidStr), "%d", tid); > + > + char pidPath[256]; > + char tidPath[256]; > + > + snprintf(pidPath, sizeof(pidPath), "/proc/%s", pidStr); > + snprintf(tidPath, sizeof(tidPath), "/proc/%s/task/%s", pidStr, tidStr); > + > + /* Check if the TID directory exists within the PID directory */ > + if (access(tidPath, F_OK) == 0) { > + return true; > + } > + > + return false; > +} > + > +/* > + * Only the RAPL MSR in target/i386/cpu.h are allowed > + */ > +static bool is_msr_allowed(uint32_t reg) > +{ > + switch (reg) { > + case MSR_RAPL_POWER_UNIT: > + case MSR_PKG_POWER_LIMIT: > + case MSR_PKG_ENERGY_STATUS: > + case MSR_PKG_POWER_INFO: > + return true; > + default: > + return false; > + } > +} > + /* > + * Check peer credentials > + * Only QEMU PID/TID are allowed This says only QEMU is allowed > + */ > + qio_channel_get_peercred(QIO_CHANNEL(client->ioc), &cred, &local_err); > + > + if (cred.pid == 0) { > + if (local_err != NULL) { > + error_report_err(local_err); > + } > + error_report("Failed to get peer credentials"); > + goto out; > + } > + > + /* > + * Read the requested MSR > + * Only RAPL MSR in rapl-msr-index.h is allowed > + */ > + r = qio_channel_read_all(QIO_CHANNEL(client->ioc), > + (char *) &request, sizeof(request), NULL); > + if (!is_msr_allowed(request[0]) || r < 0) { > + error_report("Read request fail: %d, %d", request[0], request[1]); > + goto out; > + } > + > + vmsr = vmsr_read_msr(request[0], request[1]); > + > + if (!is_tid_present(cred.pid, request[2])) { > + error_report("requested TID not in peer PID"); > + vmsr = 0; > + } This check is merely validating the the thread ID in the message is a child of the process ID connected to the socket. Any process on the entire host can satisfy this requirement. I don't see what is limiting this to only QEMU as claimed earlier, unless you're expecting the UNIX socket permissions to be such that only processes under the qemu:qemu user:group pair can access to the socket ? That would be a libvirt based permissions assumption though. > + > + r = qio_channel_write_all(QIO_CHANNEL(client->ioc), > + (char *) &vmsr, sizeof(vmsr), NULL); > + if (r < 0) { > + error_report("write vmsr failed"); > + goto out; > + } > + > +out: > + object_unref(OBJECT(client->ioc)); > + g_free(client); > +} With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|