Re: [PATCH] powerpc64/ftrace: fix module loading without patchable function entries

[Adam Williamson <awilliam@redhat.com>]

On Thu, 2025-02-13 at 22:29 +0530, Naveen N Rao wrote:
> On Wed, Feb 05, 2025 at 12:18:21AM +0100, Anthony Iliopoulos wrote:
> > get_stubs_size assumes that there must always be at least one patchable
> > function entry, which is not always the case (modules that export data
> > but no code), otherwise it returns -ENOEXEC and thus the section header
> > sh_size is set to that value. During module_memory_alloc() the size is
> > passed to execmem_alloc() after being page-aligned and thus set to zero
> > which will cause it to fail the allocation (and thus module loading) as
> > __vmalloc_node_range() checks for zero-sized allocs and returns null:
> > 
> > [  115.466896] module_64: cast_common: doesn't contain __patchable_function_entries.
> > [  115.469189] ------------[ cut here ]------------
> > [  115.469496] WARNING: CPU: 0 PID: 274 at mm/vmalloc.c:3778 __vmalloc_node_range_noprof+0x8b4/0x8f0
> > ...
> > [  115.478574] ---[ end trace 0000000000000000 ]---
> > [  115.479545] execmem: unable to allocate memory
> 
> Ugh, that's nasty.
> 
> > 
> > Fix this by removing the check completely, since it is anyway not
> > helpful to propagate this as an error upwards.
> > 
> > Fixes: eec37961a56a ("powerpc64/ftrace: Move ftrace sequence out of line")
> > Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
> > ---
> >  arch/powerpc/kernel/module_64.c | 4 ----
> >  1 file changed, 4 deletions(-)
> > 
> 
> Thanks for fixing this. It might also be good to add a check in 
> setup_ftrace_ool_stubs(). Something like this:
> 
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 34a5aec4908f..c10a9c66cfe3 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -1125,6 +1125,10 @@ static int setup_ftrace_ool_stubs(const Elf64_Shdr *sechdrs, unsigned long addr,
>         unsigned int i, total_stubs, num_stubs;
>         struct ppc64_stub_entry *stub;
>  
> +       /* Bail out early if no traceable functions */
> +       if (!me->arch.ool_stub_count)
> +               return 0;
> +
>         total_stubs = sechdrs[me->arch.stubs_section].sh_size / sizeof(*stub);
>         num_stubs = roundup(me->arch.ool_stub_count * sizeof(struct ftrace_ool_stub),
>                             sizeof(struct ppc64_stub_entry)) / sizeof(struct ppc64_stub_entry);
> 
> 
> Regardless of that, for this patch:
> Acked-by: Naveen N Rao (AMD) <naveen@kernel.org>
> 
> 
> - Naveen
> 
Is there anything that can be done to get this bumped along? It
completely breaks networking on Fedora's power9 boxes, as it affects
the i40e module which they use.

Thanks!
-- 
Adam Williamson (he/him/his)
Fedora QA
Fedora Chat: @adamwill:fedora.im | Mastodon: @adamw@fosstodon.org
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