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 <redacted>
---
 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