Re: [PATCH] powerpc32/modules: Reserve a PLT entry for ftrace_regs_caller

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Bradley Morgan <brads@mainlining.org> writes:

> Commit 7dfbfb87c243 ("powerpc/ftrace: Activate
> HAVE_DYNAMIC_FTRACE_WITH_REGS on PPC32") made count_relocs()
> undercount the PLT entries the loader
> consumes: module_finalize_ftrace() now creates two trampolines
> (mod->arch.tramp for ftrace_caller() and mod->arch.tramp_regs for
> ftrace_regs_caller()), while count_relocs() reserves only one entry
> for ftrace.
>
> So the core .plt ends up one ppc_plt_entry (16 bytes) short. The
> walk in do_plt_call() scans for a free slot with
> "while (entry->jump[0])" and has no bound check, so once the last
> reserved slot is used up, the walk steps past the end of the section
> and patch_instruction() writes the 4-instruction trampoline into
> whatever module memory follows the .plt.
>
> Count the second entry, mirroring what module_64.c does for the same
> pair of stubs.
>
> Signed-off-by: Bradley Morgan <brads@mainlining.org>
> ---
>  arch/powerpc/kernel/module_32.c | 3 +++
>  1 file changed, 3 insertions(+)
>

Do we also need fixes and stable tag here?

Fixes: 7dfbfb87c243 ("powerpc/ftrace: Activate HAVE_DYNAMIC_FTRACE_WITH_REGS on PPC32")
Cc: stable@vger.kernel.org


-ritesh