From 069e1c07c18ac2ccecdfb5ac287a37d6fb2d7a00 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 11 Sep 2019 13:26:46 +0100 Subject: module: Fix link failure due to invalid relocation on namespace offset Commit 8651ec01daed ("module: add support for symbol namespaces.") broke linking for arm64 defconfig: | lib/crypto/arc4.o: In function `__ksymtab_arc4_setkey': | arc4.c:(___ksymtab+arc4_setkey+0x8): undefined reference to `no symbol' | lib/crypto/arc4.o: In function `__ksymtab_arc4_crypt': | arc4.c:(___ksymtab+arc4_crypt+0x8): undefined reference to `no symbol' This is because the dummy initialisation of the 'namespace_offset' field in 'struct kernel_symbol' when using EXPORT_SYMBOL on architectures with support for PREL32 locations uses an offset from an absolute address (0) in an effort to trick 'offset_to_pointer' into behaving as a NOP, allowing non-namespaced symbols to be treated in the same way as those belonging to a namespace. Unfortunately, place-relative relocations require a symbol reference rather than an absolute value and, although x86 appears to get away with this due to placing the kernel text at the top of the address space, it almost certainly results in a runtime failure if the kernel is relocated dynamically as a result of KASLR. Rework 'namespace_offset' so that a value of 0, which cannot occur for a valid namespaced symbol, indicates that the corresponding symbol does not belong to a namespace. Cc: Matthias Maennich Cc: Jessica Yu Cc: Ard Biesheuvel Cc: Catalin Marinas Fixes: 8651ec01daed ("module: add support for symbol namespaces.") Reported-by: kbuild test robot Tested-by: Matthias Maennich Tested-by: Ard Biesheuvel Reviewed-by: Matthias Maennich Acked-by: Ard Biesheuvel Signed-off-by: Will Deacon Signed-off-by: Jessica Yu --- kernel/module.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel/module.c') diff --git a/kernel/module.c b/kernel/module.c index f76efcf2043e..7ab244c4e1ba 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -547,6 +547,8 @@ static const char *kernel_symbol_name(const struct kernel_symbol *sym) static const char *kernel_symbol_namespace(const struct kernel_symbol *sym) { #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS + if (!sym->namespace_offset) + return NULL; return offset_to_ptr(&sym->namespace_offset); #else return sym->namespace; -- cgit v1.2.3