Re: [PATCH] arm64: kprobes: check the return value of set_memory_rox()

[Dev Jain]

On 04/11/25 1:15 am, Yang Shi wrote:
> Since commit a166563e7ec3 ("arm64: mm: support large block mapping when
> rodata=full"), __change_memory_common has more chance to fail due to
> memory allocation fialure when splitting page table. So check the return
> value of set_memory_rox(), then bail out if it fails otherwise we may have
> RW memory mapping for kprobes insn page.
>
> Fixes: 195a1b7d8388 ("arm64: kprobes: call set_memory_rox() for kprobe page")
> Signed-off-by: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> I actually epxected 195a1b7d8388 ("arm64: kprobes: call set_memory_rox()
> for kprobe page") can be merged in 6.17-rcX, so I just restored it to
> before commit 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in
> alloc_insn_page"), however it turned out to be merged in 6.18-rc1 and it
> is after commit a166563e7ec3 ("arm64: mm: support large block mapping when
> rodata=full"). So I made the fix tag point to it.
> And I don't think we need to backport this patch to pre-6.18.
>
>   arch/arm64/kernel/probes/kprobes.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 8ab6104a4883..43a0361a8bf0 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -49,7 +49,10 @@ void *alloc_insn_page(void)
>   	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
>   	if (!addr)
>   		return NULL;
> -	set_memory_rox((unsigned long)addr, 1);
> +	if (set_memory_rox((unsigned long)addr, 1)) {
> +		execmem_free(addr);
> +		return NULL;
> +	}
>   	return addr;
>   }

Looks obviously correct:

Reviewed-by: Dev Jain <dev.jain@xxxxxxx>

Although I got confused by why set_memory_rox() is being called; it is being used
only to handle the linear map alias perm change, which is not nice :) but I don't
see an obvious way to refactor the code to only perform the needed functionality here,
and probably this is not a hot path that we care about.

>