Messages in this thread |  | | From | Ard Biesheuvel <> | Date | Thu, 9 Jul 2020 09:55:35 +0300 | Subject | Re: [PATCH] arm64/module-plts: Consider the special case where plt_max_entries is 0 |
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On Thu, 9 Jul 2020 at 09:50, 彭浩(Richard) <richard.peng@oppo.com> wrote: > > On Wed, 8 Jul 2020 at 13:03, 彭浩(Richard) <richard.peng@oppo.com> wrote: > >> > >> > >> On Tue, Jul 07, 2020 at 07:46:08AM -0400, Peng Hao wrote: > >> >> If plt_max_entries is 0, a warning is triggered. > >> >> WARNING: CPU: 200 PID: 3000 at arch/arm64/kernel/module-plts.c:97 module_emit_plt_entry+0xa4/0x150 > >> > > >> > Which kernel are you seeing this with? There is a PLT-related change in > >> > for-next/core, and I'd like to rule if out if possible. > >> > > >> 5.6.0-rc3+ > >> >> Signed-off-by: Peng Hao <richard.peng@oppo.com> > >> >> --- > >> >> arch/arm64/kernel/module-plts.c | 3 ++- > >> >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> >> > >> >> diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > >> >> index 65b08a74aec6..1868c9ac13f2 100644 > >> >> --- a/arch/arm64/kernel/module-plts.c > >> >> +++ b/arch/arm64/kernel/module-plts.c > >> >> @@ -79,7 +79,8 @@ u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs, > >> >> int i = pltsec->plt_num_entries; > >> >> int j = i - 1; > >> >> u64 val = sym->st_value + rela->r_addend; > >> >> - > >> >> + if (pltsec->plt_max_entries == 0) > >> >> + return 0; > >> > > >> >Hmm, but if there aren't any PLTs then how do we end up here? > >> > > >> We also returned 0 when warning was triggered. > > > >That doesn't really answer the question. > > > >Apparently, you are hitting a R_AARCH64_JUMP26 or R_AARCH64_CALL26 > >relocation that operates on a b or bl instruction that is more than > >128 megabytes away from its target. > > > My understanding is that a module that calls functions that are not part of the module will use PLT. > Plt_max_entries =0 May occur if a module does not depend on other module functions. >
A PLT slot is allocated for each b or bl instruction that refers to a symbol that lives in a different section, either of the same module (e.g., bl in .init calling into .text), of another module, or of the core kernel.
I don't see how you end up with plt_max_entries in this case, though. Are you sure you have CONFIG_RANDOMIZE_BASE enabled?
> >In module_frob_arch_sections(), we count all such relocations that > >point to other sections, and allocate a PLT slot for each (and update > >plt_max_entries) accordingly. So this means that the relocation in > >question was disregarded, and this could happen for only two reasons: > >- the branch instruction and its target are both in the same section, > >in which case this section is *really* large, > >- CONFIG_RANDOMIZE_BASE is disabled, but you are still ending up in a > >situation where the modules are really far away from the core kernel > >or from other modules. > > > >Do you have a lot of [large] modules loaded when this happens? > I don’t think I have [large] modules. I'll trace which module caused this warning.
Yes please.
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