CVE-2024-38667

In the Linux kernel, the following vulnerability has been resolved:

riscv: prevent pt_regs corruption for secondary idle threads

Top of the kernel thread stack should be reserved for ptregs. However this is not the case for the idle threads of the secondary boot harts. Their stacks overlap with their ptregs, so both may get corrupted.

Similar issue has been fixed for the primary hart, see c7cdd96eca28 ("riscv: prevent stack corruption by reserving taskptregs(p) early"). However that fix was not propagated to the secondary harts. The problem has been noticed in some CPU hotplug tests with V enabled. The function smpcallin stored several registers on stack, corrupting top of ptregs structure including status field. As a result, kernel attempted to save or restore inexistent V context.