arm64/module: set trampoline section flags regardless of CONFIG_DYNAMIC_FTRACE

In the arm64 module linker script, the section .text.ftrace_trampoline is specified unconditionally regardless of whether CONFIG_DYNAMIC_FTRACE is enabled (this is simply due to the limitation that module linker scripts are not preprocessed like the vmlinux one).

Normally, for .plt and .text.ftrace_trampoline, the section flags present in the module binary wouldn't matter since module_frob_arch_sections() would assign them manually anyway. However, the arm64 module loader only sets the section flags for .text.ftrace_trampoline when CONFIG_DYNAMIC_FTRACE=y. That's only become problematic recently due to a recent change in binutils-2.35, where the .text.ftrace_trampoline section (along with the .plt section) is now marked writable and executable (WAX).

We no longer allow writable and executable sections to be loaded due to commit 5c3a7db0c7ec ("module: Harden STRICT_MODULE_RWX"), so this is causing all modules linked with binutils-2.35 to be rejected under arm64. Drop the IS_ENABLED(CONFIG_DYNAMIC_FTRACE) check in module_frob_arch_sections() so that the section flags for .text.ftrace_trampoline get properly set to SHF_EXECINSTR|SHF_ALLOC, without SHF_WRITE.

Link http://lore.kernel.org/r/20200831094651.GA16385@linux-8ccs open here

Acked-by Will Deacon <[email protected]>

Signed-off-by Jessica Yu <[email protected]>

---
 arch/arm64/kernel/module-plts.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

arch/arm64/kernel/module-plts.c +1 -3

index 0ce3a28e3347..2e224435c024 100644
@@ -305,8 +305,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
                        mod->arch.core.plt_shndx = i;
                else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
                        mod->arch.init.plt_shndx = i;
-               else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) &&
-                        !strcmp(secstrings + sechdrs[i].sh_name,
+               else if (!strcmp(secstrings + sechdrs[i].sh_name,
                                 ".text.ftrace_trampoline"))
                        tramp = sechdrs + i;
                else if (sechdrs[i].sh_type == SHT_SYMTAB)
--

2.16.4

In the arm64 module linker script, the section .text.ftrace_trampoline is specified unconditionally regardless of whether CONFIG_DYNAMIC_FTRACE is enabled (this is simply due to the limitation that module linker scripts are not preprocessed like the vmlinux one).

Normally, for .plt and .text.ftrace_trampoline, the section flags present in the module binary wouldn't matter since module_frob_arch_sections() would assign them manually anyway. However, the arm64 module loader only sets the section flags for .text.ftrace_trampoline when CONFIG_DYNAMIC_FTRACE=y. That's only become problematic recently due to a recent change in binutils-2.35, where the .text.ftrace_trampoline section (along with the .plt section) is now marked writable and executable (WAX).

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