Re: [linux-6.6.y bugreport] riscv: kprobe crash as some patchs lost

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Apr 22, 2025 at 10:58:42AM +0800, Kai Zhang wrote:
> In most recent linux-6.6.y tree,
> `arch/riscv/kernel/probes/kprobes.c::arch_prepare_ss_slot` still has the
> obsolete code:
> 
>     u32 insn = __BUG_INSN_32;
>     unsigned long offset = GET_INSN_LENGTH(p->opcode);
>     p->ainsn.api.restore = (unsigned long)p->addr + offset;
>     patch_text_nosync(p->ainsn.api.insn, &p->opcode, 1);
>     patch_text_nosync((void *)p->ainsn.api.insn + offset, &insn, 1);
> 
> The last two 1s are wrong size of written instructions , which would lead to
> kernel crash, like `insmod kprobe_example.ko` gives:
> 
> [  509.812815][ T2734] kprobe_init: Planted kprobe at 00000000c5c46130
> [  509.837606][    C5] handler_pre: <kernel_clone> p->addr =
> 0x00000000c5c46130, pc = 0xffffffff80032ee2, status = 0x200000120
> [  509.839315][    C5] Oops - illegal instruction [#1]
> 
> 
> I've tried two patchs from torvalds tree and it didn't crash again:
> 
> 51781ce8f448 riscv: Pass patch_text() the length in bytes (rebased)
> 13134cc94914 riscv: kprobes: Fix incorrect address calculation

Neither of these apply cleanly.  Please provide working backports if you
wish to see them added to the tree.

thanks,

greg k-h