CVE-2026-72028riscv: probes: save original sp in rethook trampoline

Official description

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 ... [<ffffffff80016d16>] regs_get_kernel_stack_nth+0x26/0x38 [<ffffffff80177196>] process_fetch_insn+0x3ee/0x760 [<ffffffff80177836>] kretprobe_trace_func+0x116/0x1f0 [<ffffffff8017795a>] kretprobe_dispatcher+0x4a/0x58 [<ffffffff8013572e>] kretprobe_rethook_handler+0x5e/0x90 [<ffffffff80180838>] rethook_trampoline_handler+0x70/0x108 [<ffffffff8001ba32>] arch_rethook_trampoline_callback+0x12/0x1c [<ffffffff8001ba84>] arch_rethook_trampoline+0x48/0x94 [<ffffffff8067872a>] 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_trampoline's 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; cc'ed stable]

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/d21109fe4a55247094f913773a334772907cd016
• https://git.kernel.org/stable/c/5da5cf48a432e30ded8d58087854e5383a36eff1
• https://git.kernel.org/stable/c/c386e1c591d72eab58ee2e69105c8cbc70928857
• https://git.kernel.org/stable/c/2faf0198168d2017cb528a79f76c560fda3b6e94
• https://git.kernel.org/stable/c/91b4d76dd07f1a1f20f73dfebb42ba04ac911a56
• https://git.kernel.org/stable/c/bc7b086a45521a986a49045907f017e3e46c763e