From 73f44fe19d359635a607e8e8daa0da4001c1cfc2 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 27 Jan 2021 17:18:37 -0600 Subject: static_call: Allow module use without exposing static_call_key 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) Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20210127231837.ifddpn7rhwdaepiu@treble --- tools/include/linux/static_call_types.h | 27 +++++++++++++++++++++++++-- tools/objtool/check.c | 17 +++++++++++++++-- 2 files changed, 40 insertions(+), 4 deletions(-) (limited to 'tools') diff --git a/tools/include/linux/static_call_types.h b/tools/include/linux/static_call_types.h index 08f78b1b88b4..ae5662d368b9 100644 --- a/tools/include/linux/static_call_types.h +++ b/tools/include/linux/static_call_types.h @@ -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 diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 4bd30315eb62..f2e5e5ce1a05 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -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); -- cgit v1.2.3