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 <maennich@google.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Fixes: 8651ec01daed ("module: add support for symbol namespaces.")
Reported-by: kbuild test robot <lkp@intel.com>
Tested-by: Matthias Maennich <maennich@google.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Matthias Maennich <maennich@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Jessica Yu <jeyu@kernel.org>

diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
index e2b5d0f569d3bc1c0c34f5c41c354cf4e9599d95..d0912c7ac2fc16f815cbdcb6b83f03848865b37f 100644 (file)
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -17,7 +17,7 @@
 
 .macro __put, val, name
 #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
-       .long   \val - ., \name - ., 0 - .
+       .long   \val - ., \name - ., 0
 #elif defined(CONFIG_64BIT)
        .quad   \val, \name, 0
 #else

diff --git a/include/linux/export.h b/include/linux/export.h
index 2c5468d8ea9adf16a0a0a12e33cb2d12e2b07281..ef5d015d754a6f2a6ecdb3dcce0676b7cf5e59cc 100644 (file)
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -68,7 +68,7 @@ extern struct module __this_module;
            "__ksymtab_" #sym ":                                \n"     \
            "   .long   " #sym "- .                             \n"     \
            "   .long   __kstrtab_" #sym "- .                   \n"     \
-           "   .long   0 - .                                   \n"     \
+           "   .long   0                                       \n"     \
            "   .previous                                       \n")
 
 struct kernel_symbol {

diff --git a/kernel/module.c b/kernel/module.c
index f76efcf2043ef32cf9044dc0db81610bf2fe4845..7ab244c4e1ba4b43cb65f0fd9cee405754210566 100644 (file)
--- 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;