In the Linux kernel, the following vulnerability has been resolved:
riscv: probes: save original sp in rethook trampoline
Reading a word from the stack in a kretprobe crashes a risc-v kernel.
$ cd /sys/kernel/tracing/ $ echo r n_tty_write $stack0 > dynamic_events $ echo 1 > events/kprobes/enable Unable to handle kernel paging request at virtual address 0000000200000128 … [] regs_get_kernel_stack_nth+0x26/0x38 [] process_fetch_insn+0x3ee/0x760 [] kretprobe_trace_func+0x116/0x1f0 [] kretprobe_dispatcher+0x4a/0x58 [] kretprobe_rethook_handler+0x5e/0x90 [] rethook_trampoline_handler+0x70/0x108 [] arch_rethook_trampoline_callback+0x12/0x1c [] arch_rethook_trampoline+0x48/0x94 [] tty_write+0x1a/0x30
In regs_get_kernel_stack_nth, regs->sp contains an arbitrary value.
arch_rethook_trampoline saves the registers from the probed function in a struct pt_regs. sp is not saved. Instead, sp is decremented for arch_rethook_trampolines local stack.
Fix this crash and save the original sp along with the other registers. Use a0 as a temporary register, it is overwritten anyway.
[pjw@kernel.org: added Fixes tag; cced stable]
References
- https://git.kernel.org/stable/c/2faf0198168d2017cb528a79f76c560fda3b6e94
- https://git.kernel.org/stable/c/5da5cf48a432e30ded8d58087854e5383a36eff1
- https://git.kernel.org/stable/c/91b4d76dd07f1a1f20f73dfebb42ba04ac911a56
- https://git.kernel.org/stable/c/bc7b086a45521a986a49045907f017e3e46c763e
- https://git.kernel.org/stable/c/c386e1c591d72eab58ee2e69105c8cbc70928857