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

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Message-ID: <YMdGWjBOmcstBwOl@p200300cbcf109700df096d564fe976c3.dip0.t-ipconnect.de>
Date:   Mon, 14 Jun 2021 14:06:50 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Michal Suchánek <msuchanek@...e.de>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v4 1/2] module: add elf_check_module_arch for module
 specific elf arch checks

+++ 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.

Thanks,

Jessica

>+
> /* 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..7c3f9b7478dc 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -2946,7 +2946,7 @@ static int elf_validity_check(struct load_info *info)
>
> 	if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0
> 	    || info->hdr->e_type != ET_REL
>-	    || !elf_check_arch(info->hdr)
>+	    || !elf_check_module_arch(info->hdr)
> 	    || info->hdr->e_shentsize != sizeof(Elf_Shdr))
> 		return -ENOEXEC;
>
>-- 
>2.23.0
>