linux-kernel - Re: [PATCH v4 1/2] module: add elf_check_module

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Date:   Tue, 15 Jun 2021 12:05:51 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Suchánek <msuchanek@...e.de>
Subject: Re: [PATCH v4 1/2] module: add elf_check_module_arch for module
 specific elf arch checks

Excerpts from Jessica Yu's message of June 14, 2021 10:06 pm:
> +++ Nicholas Piggin [11/06/21 19:39 +1000]:
>>The elf_check_arch() function is used to test usermode binaries, but
>>kernel modules may have more specific requirements. powerpc would like
>>to test for ABI version compatibility.
>>
>>Add an arch-overridable function elf_check_module_arch() that defaults
>>to elf_check_arch() and use it in elf_validity_check().
>>
>>Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
>>[np: split patch, added changelog]
>>Signed-off-by: Nicholas Piggin <npiggin@...il.com>
>>---
>> include/linux/moduleloader.h | 5 +++++
>> kernel/module.c              | 2 +-
>> 2 files changed, 6 insertions(+), 1 deletion(-)
>>
>>diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
>>index 9e09d11ffe5b..fdc042a84562 100644
>>--- a/include/linux/moduleloader.h
>>+++ b/include/linux/moduleloader.h
>>@@ -13,6 +13,11 @@
>>  * must be implemented by each architecture.
>>  */
>>
>>+// Allow arch to optionally do additional checking of module ELF header
>>+#ifndef elf_check_module_arch
>>+#define elf_check_module_arch elf_check_arch
>>+#endif
> 
> Hi Nicholas,
> 
> Why not make elf_check_module_arch() consistent with the other
> arch-specific functions? Please see module_frob_arch_sections(),
> module_{init,exit}_section(), etc in moduleloader.h. That is, they are
> all __weak functions that are overridable by arches. We can maybe make
> elf_check_module_arch() a weak symbol, available for arches to
> override if they want to perform additional elf checks. Then we don't
> have to have this one-off #define.


Like this? I like it. Good idea.

Thanks,
Nick

diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
index 9e09d11ffe5b..7b4587a19189 100644
--- a/include/linux/moduleloader.h
+++ b/include/linux/moduleloader.h
@@ -13,6 +13,9 @@
  * must be implemented by each architecture.
  */
 
+/* arch may override to do additional checking of ELF header architecture */
+bool module_elf_check_arch(Elf_Ehdr *hdr);
+
 /* Adjust arch-specific sections.  Return 0 on success.  */
 int module_frob_arch_sections(Elf_Ehdr *hdr,
 			      Elf_Shdr *sechdrs,
diff --git a/kernel/module.c b/kernel/module.c
index 7e78dfabca97..8b31c0b7c2a0 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3459,6 +3459,11 @@ static void flush_module_icache(const struct module *mod)
 			   (unsigned long)mod->core_layout.base + mod->core_layout.size);
 }
 
+bool __weak module_elf_check_arch(Elf_Ehdr *hdr)
+{
+	return elf_check_arch(hdr);
+}
+
 int __weak module_frob_arch_sections(Elf_Ehdr *hdr,
 				     Elf_Shdr *sechdrs,
 				     char *secstrings,