From: Martin Kaiser Date: Tue, 30 Jun 2026 19:40:03 +0000 (+0200) Subject: riscv: probes: save original sp in rethook trampoline X-Git-Tag: v7.2-rc2~12^2 X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=bc7b086a45521a986a49045907f017e3e46c763e;p=thirdparty%2Flinux.git 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_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. Cc: stable@vger.kernel.org Fixes: c22b0bcb1dd02 ("riscv: Add kprobes supported") Signed-off-by: Martin Kaiser Acked-by: Masami Hiramatsu (Google) Link: https://patch.msgid.link/20260630194010.1824039-1-martin@kaiser.cx [pjw@kernel.org: added Fixes tag; cc'ed stable] Signed-off-by: Paul Walmsley --- diff --git a/arch/riscv/kernel/probes/rethook_trampoline.S b/arch/riscv/kernel/probes/rethook_trampoline.S index f2cd83d9b0f0..c3aa8d8cf5af 100644 --- a/arch/riscv/kernel/probes/rethook_trampoline.S +++ b/arch/riscv/kernel/probes/rethook_trampoline.S @@ -41,6 +41,9 @@ REG_S x29, PT_T4(sp) REG_S x30, PT_T5(sp) REG_S x31, PT_T6(sp) + /* save original sp */ + addi a0, sp, PT_SIZE_ON_STACK + REG_S a0, PT_SP(sp) .endm .macro restore_all_base_regs