Re: [PATCH v4 1/2] module: add elf_check_module_arch for module specific elf arch checks
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From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2021-06-16 02:37:18
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Jessica Yu [off-list ref] writes:
quoted hunk ↗ jump to hunk
+++ Nicholas Piggin [15/06/21 12:05 +1000]:quoted
Excerpts from Jessica Yu's message of June 14, 2021 10:06 pm:quoted
+++ Nicholas Piggin [11/06/21 19:39 +1000]:quoted
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@ellerman.id.au> [np: split patch, added changelog] Signed-off-by: Nicholas Piggin <npiggin@gmail.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 +#endifHi 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.
quoted
Like this? I like it. Good idea.Yeah! Also, maybe we can alternatively make elf_check_module_arch() a separate check entirely so that the powerpc implementation doesn't have to include that extra elf_check_arch() call. Something like this maybe?
My thinking for making elf_check_module_arch() the only hook was that conceivably you might not want/need to call elf_check_arch() from elf_check_module_arch(). So having a single module specific hook allows arch code to decide how to implement the check, which may or may not involve calling elf_check_arch(), but that becomes an arch implementation detail. It's also one arch hook instead of two (although elf_check_arch() already exists). But I don't feel that strongly either way, whatever you prefer. cheers