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069e1c07c18ac2ccecdfb5ac287a37d6fb2d7a00
linux_media/include/linux/export.h
Will Deacon 069e1c07c1 module: Fix link failure due to invalid relocation on namespace offset 
Commit 8651ec01da ("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: 8651ec01da ("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>
2019-09-11 18:53:30 +02:00

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#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H
/*
* Export symbols from the kernel to modules. Forked from module.h
* to reduce the amount of pointless cruft we feed to gcc when only
* exporting a simple symbol or two.
*
* Try not to add #includes here. It slows compilation and makes kernel
* hackers place grumpy comments in header files.
*/
#ifndef __ASSEMBLY__
#ifdef MODULE
extern struct module __this_module;
#define THIS_MODULE (&__this_module)
#else
#define THIS_MODULE ((struct module *)0)
#endif
#ifdef CONFIG_MODULES
#define NS_SEPARATOR "."
#if defined(__KERNEL__) && !defined(__GENKSYMS__)
#ifdef CONFIG_MODVERSIONS
/* Mark the CRC weak since genksyms apparently decides not to
* generate a checksums for some symbols */
#if defined(CONFIG_MODULE_REL_CRCS)
#define __CRC_SYMBOL(sym, sec) \
asm(" .section \"___kcrctab" sec "+" #sym "\", \"a\" \n" \
" .weak __crc_" #sym " \n" \
" .long __crc_" #sym " - . \n" \
" .previous \n")
#else
#define __CRC_SYMBOL(sym, sec) \
asm(" .section \"___kcrctab" sec "+" #sym "\", \"a\" \n" \
" .weak __crc_" #sym " \n" \
" .long __crc_" #sym " \n" \
" .previous \n")
#endif
#else
#define __CRC_SYMBOL(sym, sec)
#endif
#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
#include <linux/compiler.h>
/*
* Emit the ksymtab entry as a pair of relative references: this reduces
* the size by half on 64-bit architectures, and eliminates the need for
* absolute relocations that require runtime processing on relocatable
* kernels.
*/
#define __KSYMTAB_ENTRY_NS(sym, sec, ns) \
__ADDRESSABLE(sym) \
asm(" .section \"___ksymtab" sec "+" #sym "\", \"a\" \n" \
" .balign 4 \n" \
"__ksymtab_" #sym NS_SEPARATOR #ns ": \n" \
" .long " #sym "- . \n" \
" .long __kstrtab_" #sym "- . \n" \
" .long __kstrtab_ns_" #sym "- . \n" \
" .previous \n")
#define __KSYMTAB_ENTRY(sym, sec) \
__ADDRESSABLE(sym) \
asm(" .section \"___ksymtab" sec "+" #sym "\", \"a\" \n" \
" .balign 4 \n" \
"__ksymtab_" #sym ": \n" \
" .long " #sym "- . \n" \
" .long __kstrtab_" #sym "- . \n" \
" .long 0 \n" \
" .previous \n")
struct kernel_symbol {
int value_offset;
int name_offset;
int namespace_offset;
};
#else
#define __KSYMTAB_ENTRY_NS(sym, sec, ns) \
static const struct kernel_symbol __ksymtab_##sym##__##ns \
asm("__ksymtab_" #sym NS_SEPARATOR #ns) \
__attribute__((section("___ksymtab" sec "+" #sym), used)) \
__aligned(sizeof(void *)) \
= { (unsigned long)&sym, __kstrtab_##sym, __kstrtab_ns_##sym }
#define __KSYMTAB_ENTRY(sym, sec) \
static const struct kernel_symbol __ksymtab_##sym \
asm("__ksymtab_" #sym) \
__attribute__((section("___ksymtab" sec "+" #sym), used)) \
__aligned(sizeof(void *)) \
= { (unsigned long)&sym, __kstrtab_##sym, NULL }
struct kernel_symbol {
unsigned long value;
const char *name;
const char *namespace;
};
#endif
#define ___export_symbol_common(sym, sec) \
extern typeof(sym) sym; \
__CRC_SYMBOL(sym, sec); \
static const char __kstrtab_##sym[] \
__attribute__((section("__ksymtab_strings"), used, aligned(1))) \
= #sym \
/* For every exported symbol, place a struct in the __ksymtab section */
#define ___EXPORT_SYMBOL_NS(sym, sec, ns) \
___export_symbol_common(sym, sec); \
static const char __kstrtab_ns_##sym[] \
__attribute__((section("__ksymtab_strings"), used, aligned(1))) \
= #ns; \
__KSYMTAB_ENTRY_NS(sym, sec, ns)
#define ___EXPORT_SYMBOL(sym, sec) \
___export_symbol_common(sym, sec); \
__KSYMTAB_ENTRY(sym, sec)
#if defined(__DISABLE_EXPORTS)
/*
* Allow symbol exports to be disabled completely so that C code may
* be reused in other execution contexts such as the UEFI stub or the
* decompressor.
*/
#define __EXPORT_SYMBOL_NS(sym, sec, ns)
#define __EXPORT_SYMBOL(sym, sec)
#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
#include <generated/autoksyms.h>
/*
* For fine grained build dependencies, we want to tell the build system
* about each possible exported symbol even if they're not actually exported.
* We use a symbol pattern __ksym_marker_<symbol> that the build system filters
* from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
* discarded in the final link stage.
*/
#define __ksym_marker(sym) \
static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
#define __EXPORT_SYMBOL(sym, sec) \
__ksym_marker(sym); \
__cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
#define __cond_export_sym(sym, sec, conf) \
___cond_export_sym(sym, sec, conf)
#define ___cond_export_sym(sym, sec, enabled) \
__cond_export_sym_##enabled(sym, sec)
#define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec)
#define __cond_export_sym_0(sym, sec) /* nothing */
#define __EXPORT_SYMBOL_NS(sym, sec, ns) \
__ksym_marker(sym); \
__cond_export_ns_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
#define __cond_export_ns_sym(sym, sec, ns, conf) \
___cond_export_ns_sym(sym, sec, ns, conf)
#define ___cond_export_ns_sym(sym, sec, ns, enabled) \
__cond_export_ns_sym_##enabled(sym, sec, ns)
#define __cond_export_ns_sym_1(sym, sec, ns) ___EXPORT_SYMBOL_NS(sym, sec, ns)
#define __cond_export_ns_sym_0(sym, sec, ns) /* nothing */
#else
#define __EXPORT_SYMBOL_NS ___EXPORT_SYMBOL_NS
#define __EXPORT_SYMBOL ___EXPORT_SYMBOL
#endif
#ifdef DEFAULT_SYMBOL_NAMESPACE
#undef __EXPORT_SYMBOL
#define __EXPORT_SYMBOL(sym, sec) \
__EXPORT_SYMBOL_NS(sym, sec, DEFAULT_SYMBOL_NAMESPACE)
#endif
#define EXPORT_SYMBOL(sym) __EXPORT_SYMBOL(sym, "")
#define EXPORT_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_gpl")
#define EXPORT_SYMBOL_GPL_FUTURE(sym) __EXPORT_SYMBOL(sym, "_gpl_future")
#define EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL_NS(sym, "", ns)
#define EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL_NS(sym, "_gpl", ns)
#ifdef CONFIG_UNUSED_SYMBOLS
#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused")
#define EXPORT_UNUSED_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_unused_gpl")
#else
#define EXPORT_UNUSED_SYMBOL(sym)
#define EXPORT_UNUSED_SYMBOL_GPL(sym)
#endif
#endif /* __KERNEL__ && !__GENKSYMS__ */
#if defined(__GENKSYMS__)
/*
* When we're running genksyms, ignore the namespace and make the _NS
* variants look like the normal ones. There are two reasons for this:
* 1) In the normal definition of EXPORT_SYMBOL_NS, the 'ns' macro
* argument is itself not expanded because it's always tokenized or
* concatenated; but when running genksyms, a blank definition of the
* macro does allow the argument to be expanded; if a namespace
* happens to collide with a #define, this can cause issues.
* 2) There's no need to modify genksyms to deal with the _NS variants
*/
#define EXPORT_SYMBOL_NS(sym, ns) EXPORT_SYMBOL(sym)
#define EXPORT_SYMBOL_NS_GPL(sym, ns) EXPORT_SYMBOL_GPL(sym)
#endif
#else /* !CONFIG_MODULES... */
#define EXPORT_SYMBOL(sym)
#define EXPORT_SYMBOL_NS(sym, ns)
#define EXPORT_SYMBOL_NS_GPL(sym, ns)
#define EXPORT_SYMBOL_GPL(sym)
#define EXPORT_SYMBOL_GPL_FUTURE(sym)
#define EXPORT_UNUSED_SYMBOL(sym)
#define EXPORT_UNUSED_SYMBOL_GPL(sym)
#endif /* CONFIG_MODULES */
#endif /* !__ASSEMBLY__ */
#endif /* _LINUX_EXPORT_H */
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