CVE-2022-49955

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> powerpc/rtas: Fix RTAS MSR[HV] handling for Cell<br /> <br /> The semi-recent changes to MSR handling when entering RTAS (firmware)<br /> cause crashes on IBM Cell machines. An example trace:<br /> <br /> kernel tried to execute user page (2fff01a8) - exploit attempt? (uid: 0)<br /> BUG: Unable to handle kernel instruction fetch<br /> Faulting instruction address: 0x2fff01a8<br /> Oops: Kernel access of bad area, sig: 11 [#1]<br /> BE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=4 NUMA Cell<br /> Modules linked in:<br /> CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.0.0-rc2-00433-gede0a8d3307a #207<br /> NIP: 000000002fff01a8 LR: 0000000000032608 CTR: 0000000000000000<br /> REGS: c0000000015236b0 TRAP: 0400 Tainted: G W (6.0.0-rc2-00433-gede0a8d3307a)<br /> MSR: 0000000008001002 CR: 00000000 XER: 20000000<br /> ...<br /> NIP 0x2fff01a8<br /> LR 0x32608<br /> Call Trace:<br /> 0xc00000000143c5f8 (unreliable)<br /> .rtas_call+0x224/0x320<br /> .rtas_get_boot_time+0x70/0x150<br /> .read_persistent_clock64+0x114/0x140<br /> .read_persistent_wall_and_boot_offset+0x24/0x80<br /> .timekeeping_init+0x40/0x29c<br /> .start_kernel+0x674/0x8f0<br /> start_here_common+0x1c/0x50<br /> <br /> Unlike PAPR platforms where RTAS is only used in guests, on the IBM Cell<br /> machines Linux runs with MSR[HV] set but also uses RTAS, provided by<br /> SLOF.<br /> <br /> Fix it by copying the MSR[HV] bit from the MSR value we&amp;#39;ve just read<br /> using mfmsr into the value used for RTAS.<br /> <br /> It seems like we could also fix it using an #ifdef CELL to set MSR[HV],<br /> but that doesn&amp;#39;t work because it&amp;#39;s possible to build a single kernel<br /> image that runs on both Cell native and pseries.