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. Signed-off-by: Martin Kaiser <[email protected]> --- arch/riscv/kernel/probes/rethook_trampoline.S | 3 +++ 1 file changed, 3 insertions(+) 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 -- 2.43.7
