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static_call: Allow module use without exposing static_call_key

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When exporting static_call_key; with EXPORT_STATIC_CALL*(), the module
can use static_call_update() to change the function called.  This is
not desirable in general.

Not exporting static_call_key however also disallows usage of
static_call(), since objtool needs the key to construct the
static_call_site.

Solve this by allowing objtool to create the static_call_site using
the trampoline address when it builds a module and cannot find the
static_call_key symbol. The module loader will then try and map the
trampole back to a key before it constructs the normal sites list.

Doing this requires a trampoline -> key associsation, so add another
magic section that keeps those.

Originally-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210127231837.ifddpn7rhwdaepiu@treble
This commit is contained in:
Josh Poimboeuf 2021-01-27 17:18:37 -06:00 committed by Ingo Molnar
parent e59e10f8ef
commit 73f44fe19d
7 changed files with 149 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
arch/x86/include/asm/static_call.h
View File

@ -37,4 +37,11 @@
#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) \
__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")
#define ARCH_ADD_TRAMP_KEY(name) \
asm(".pushsection .static_call_tramp_key, \"a\" \n" \
".long " STATIC_CALL_TRAMP_STR(name) " - . \n" \
".long " STATIC_CALL_KEY_STR(name) " - . \n" \
".popsection \n")
#endif /* _ASM_STATIC_CALL_H */

5
include/asm-generic/vmlinux.lds.h
View File

@ -393,7 +393,10 @@
. = ALIGN(8); \
__start_static_call_sites = .; \
KEEP(*(.static_call_sites)) \
__stop_static_call_sites = .;
__stop_static_call_sites = .; \
__start_static_call_tramp_key = .; \
KEEP(*(.static_call_tramp_key)) \
__stop_static_call_tramp_key = .;
/*
* Allow architectures to handle ro_after_init data on their

22
include/linux/static_call.h
View File

@ -138,6 +138,12 @@ struct static_call_key {
};
};
/* For finding the key associated with a trampoline */
struct static_call_tramp_key {
s32 tramp;
s32 key;
};
extern void __static_call_update(struct static_call_key *key, void *tramp, void *func);
extern int static_call_mod_init(struct module *mod);
extern int static_call_text_reserved(void *start, void *end);
@ -165,11 +171,18 @@ extern long __static_call_return0(void);
#define EXPORT_STATIC_CALL(name) \
EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
#define EXPORT_STATIC_CALL_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
/* Leave the key unexported, so modules can't change static call targets: */
#define EXPORT_STATIC_CALL_TRAMP(name) \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name)); \
ARCH_ADD_TRAMP_KEY(name)
#define EXPORT_STATIC_CALL_TRAMP_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name)); \
ARCH_ADD_TRAMP_KEY(name)
#elif defined(CONFIG_HAVE_STATIC_CALL)
static inline int static_call_init(void) { return 0; }
@ -216,11 +229,16 @@ static inline long __static_call_return0(void)
#define EXPORT_STATIC_CALL(name) \
EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
#define EXPORT_STATIC_CALL_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
/* Leave the key unexported, so modules can't change static call targets: */
#define EXPORT_STATIC_CALL_TRAMP(name) \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
#define EXPORT_STATIC_CALL_TRAMP_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
#else /* Generic implementation */
static inline int static_call_init(void) { return 0; }

27
include/linux/static_call_types.h
View File

@ -10,6 +10,7 @@
#define STATIC_CALL_KEY_PREFIX_STR __stringify(STATIC_CALL_KEY_PREFIX)
#define STATIC_CALL_KEY_PREFIX_LEN (sizeof(STATIC_CALL_KEY_PREFIX_STR) - 1)
#define STATIC_CALL_KEY(name) __PASTE(STATIC_CALL_KEY_PREFIX, name)
#define STATIC_CALL_KEY_STR(name) __stringify(STATIC_CALL_KEY(name))
#define STATIC_CALL_TRAMP_PREFIX __SCT__
#define STATIC_CALL_TRAMP_PREFIX_STR __stringify(STATIC_CALL_TRAMP_PREFIX)
@ -39,17 +40,39 @@ struct static_call_site {
#ifdef CONFIG_HAVE_STATIC_CALL
#define __raw_static_call(name) (&STATIC_CALL_TRAMP(name))
#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
/*
* __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
* the symbol table so that objtool can reference it when it generates the
* .static_call_sites section.
*/
#define __STATIC_CALL_ADDRESSABLE(name) \
__ADDRESSABLE(STATIC_CALL_KEY(name))
#define __static_call(name) \
({ \
__ADDRESSABLE(STATIC_CALL_KEY(name)); \
&STATIC_CALL_TRAMP(name); \
__STATIC_CALL_ADDRESSABLE(name); \
__raw_static_call(name); \
})
#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */
#define __STATIC_CALL_ADDRESSABLE(name)
#define __static_call(name) __raw_static_call(name)
#endif /* CONFIG_HAVE_STATIC_CALL_INLINE */
#ifdef MODULE
#define __STATIC_CALL_MOD_ADDRESSABLE(name)
#define static_call_mod(name) __raw_static_call(name)
#else
#define __STATIC_CALL_MOD_ADDRESSABLE(name) __STATIC_CALL_ADDRESSABLE(name)
#define static_call_mod(name) __static_call(name)
#endif
#define static_call(name) __static_call(name)
#else

55
kernel/static_call.c
View File

@ -12,6 +12,8 @@
extern struct static_call_site __start_static_call_sites[],
__stop_static_call_sites[];
extern struct static_call_tramp_key __start_static_call_tramp_key[],
__stop_static_call_tramp_key[];
static bool static_call_initialized;
@ -323,10 +325,59 @@ static int __static_call_mod_text_reserved(void *start, void *end)
return ret;
}
static unsigned long tramp_key_lookup(unsigned long addr)
{
struct static_call_tramp_key *start = __start_static_call_tramp_key;
struct static_call_tramp_key *stop = __stop_static_call_tramp_key;
struct static_call_tramp_key *tramp_key;
for (tramp_key = start; tramp_key != stop; tramp_key++) {
unsigned long tramp;
tramp = (long)tramp_key->tramp + (long)&tramp_key->tramp;
if (tramp == addr)
return (long)tramp_key->key + (long)&tramp_key->key;
}
return 0;
}
static int static_call_add_module(struct module *mod)
{
return __static_call_init(mod, mod->static_call_sites,
mod->static_call_sites + mod->num_static_call_sites);
struct static_call_site *start = mod->static_call_sites;
struct static_call_site *stop = start + mod->num_static_call_sites;
struct static_call_site *site;
for (site = start; site != stop; site++) {
unsigned long addr = (unsigned long)static_call_key(site);
unsigned long key;
/*
* Is the key is exported, 'addr' points to the key, which
* means modules are allowed to call static_call_update() on
* it.
*
* Otherwise, the key isn't exported, and 'addr' points to the
* trampoline so we need to lookup the key.
*
* We go through this dance to prevent crazy modules from
* abusing sensitive static calls.
*/
if (!kernel_text_address(addr))
continue;
key = tramp_key_lookup(addr);
if (!key) {
pr_warn("Failed to fixup __raw_static_call() usage at: %ps\n",
static_call_addr(site));
return -EINVAL;
}
site->key = (key - (long)&site->key) |
(site->key & STATIC_CALL_SITE_FLAGS);
}
return __static_call_init(mod, start, stop);
}
static void static_call_del_module(struct module *mod)

27
tools/include/linux/static_call_types.h
View File

@ -10,6 +10,7 @@
#define STATIC_CALL_KEY_PREFIX_STR __stringify(STATIC_CALL_KEY_PREFIX)
#define STATIC_CALL_KEY_PREFIX_LEN (sizeof(STATIC_CALL_KEY_PREFIX_STR) - 1)
#define STATIC_CALL_KEY(name) __PASTE(STATIC_CALL_KEY_PREFIX, name)
#define STATIC_CALL_KEY_STR(name) __stringify(STATIC_CALL_KEY(name))
#define STATIC_CALL_TRAMP_PREFIX __SCT__
#define STATIC_CALL_TRAMP_PREFIX_STR __stringify(STATIC_CALL_TRAMP_PREFIX)
@ -39,17 +40,39 @@ struct static_call_site {
#ifdef CONFIG_HAVE_STATIC_CALL
#define __raw_static_call(name) (&STATIC_CALL_TRAMP(name))
#ifdef CONFIG_HAVE_STATIC_CALL_INLINE
/*
* __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from
* the symbol table so that objtool can reference it when it generates the
* .static_call_sites section.
*/
#define __STATIC_CALL_ADDRESSABLE(name) \
__ADDRESSABLE(STATIC_CALL_KEY(name))
#define __static_call(name) \
({ \
__ADDRESSABLE(STATIC_CALL_KEY(name)); \
&STATIC_CALL_TRAMP(name); \
__STATIC_CALL_ADDRESSABLE(name); \
__raw_static_call(name); \
})
#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */
#define __STATIC_CALL_ADDRESSABLE(name)
#define __static_call(name) __raw_static_call(name)
#endif /* CONFIG_HAVE_STATIC_CALL_INLINE */
#ifdef MODULE
#define __STATIC_CALL_MOD_ADDRESSABLE(name)
#define static_call_mod(name) __raw_static_call(name)
#else
#define __STATIC_CALL_MOD_ADDRESSABLE(name) __STATIC_CALL_ADDRESSABLE(name)
#define static_call_mod(name) __static_call(name)
#endif
#define static_call(name) __static_call(name)
#else

17
tools/objtool/check.c
View File

@ -502,8 +502,21 @@ static int create_static_call_sections(struct objtool_file *file)
key_sym = find_symbol_by_name(file->elf, tmp);
if (!key_sym) {
WARN("static_call: can't find static_call_key symbol: %s", tmp);
return -1;
if (!module) {
WARN("static_call: can't find static_call_key symbol: %s", tmp);
return -1;
}
/*
* For modules(), the key might not be exported, which
* means the module can make static calls but isn't
* allowed to change them.
*
* In that case we temporarily set the key to be the
* trampoline address. This is fixed up in
* static_call_add_module().
*/
key_sym = insn->call_dest;
}
free(key_name);