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

[Yang Shi]

On 11/4/25 6:02 AM, Dev Jain wrote:
> 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>

Thank you.

> 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.

Catalin actually raised the similar suggestion before. He suggested 
extract the linear mapping update code into a helper then just call it 
here if I remember correctly. However I have not gotten time to look it 
deeper yet. Anyway we agree it is not a critical path. It may be not 
worth all the effort.

Thanks,
Yang


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