| Message ID | 20181204141415.969-2-vincent.whitchurch@axis.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v5,1/2] module: Overwrite st_size instead of st_info | expand |
+++ Vincent Whitchurch [04/12/18 15:14 +0100]: >Thumb-2 functions have the lowest bit set in the symbol value in the >symtab. When kallsyms are generated for the vmlinux, the kallsyms are >generated from the output of nm, and nm clears the lowest bit. > > $ arm-linux-gnueabihf-readelf -a vmlinux | grep show_interrupts > 95947: 8015dc89 686 FUNC GLOBAL DEFAULT 2 show_interrupts > $ arm-linux-gnueabihf-nm vmlinux | grep show_interrupts > 8015dc88 T show_interrupts > $ cat /proc/kallsyms | grep show_interrupts > 8015dc88 T show_interrupts > >However, for modules, the kallsyms uses the values in the symbol table >without modification, so for functions in modules, the lowest bit is set >in kallsyms. > > $ arm-linux-gnueabihf-readelf -a drivers/net/tun.ko | grep tun_get_socket > 333: 00002d4d 36 FUNC GLOBAL DEFAULT 1 tun_get_socket > $ arm-linux-gnueabihf-nm drivers/net/tun.ko | grep tun_get_socket > 00002d4c T tun_get_socket > $ cat /proc/kallsyms | grep tun_get_socket > 7f802d4d t tun_get_socket [tun] > >Because of this, the symbol+offset of the crashing instruction shown in >oopses is incorrect when the crash is in a module. For example, given a >tun_get_socket which starts like this, > > 00002d4c <tun_get_socket>: > 2d4c: 6943 ldr r3, [r0, #20] > 2d4e: 4a07 ldr r2, [pc, #28] > 2d50: 4293 cmp r3, r2 > >a crash when tun_get_socket is called with NULL results in: > > PC is at tun_xdp+0xa3/0xa4 [tun] > pc : [<7f802d4c>] > >As can be seen, the "PC is at" line reports the wrong symbol name, and >the symbol+offset will point to the wrong source line if it is passed to >gdb. > >To solve this, add a way for archs to fixup the reading of these module >kallsyms values, and use that to clear the lowest bit for function >symbols on Thumb-2. > >After the fix: > > # cat /proc/kallsyms | grep tun_get_socket > 7f802d4c t tun_get_socket [tun] > > PC is at tun_get_socket+0x0/0x24 [tun] > pc : [<7f802d4c>] > >Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> Looks good, could I get an ACK from an ARM maintainer? (Russell?) Also, do you mind if I drop the module_ prefix from module_kallsyms_symbol_value()? I recently submitted some internal module kallsyms cleanups [1] and there we have the newly renamed kallsyms_symbol_name(), so I think it'd be nice if we kept the naming scheme consistent with just kallsyms_symbol_value(). I could just do this myself if you don't want to respin a v6. Thanks! Jessica [1] https://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux.git/commit/?h=modules-next&id=2d25bc55235314d869459c574be14e8faa73aca3 >--- >v5: Use/move local variables to reduce calls and keep lines short. Use const arg. >v4: Split out st_value overwrite change. Add HAVE* macro to avoid function call. >v3: Do not overwrite st_value >v2: Fix build warning with !MODULES > > arch/arm/include/asm/module.h | 11 +++++++++++ > include/linux/module.h | 7 +++++++ > kernel/module.c | 45 +++++++++++++++++++++++++++---------------- > 3 files changed, 46 insertions(+), 17 deletions(-) > >diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h >index 9e81b7c498d8..c7bcf0347801 100644 >--- a/arch/arm/include/asm/module.h >+++ b/arch/arm/include/asm/module.h >@@ -61,4 +61,15 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val); > MODULE_ARCH_VERMAGIC_ARMTHUMB \ > MODULE_ARCH_VERMAGIC_P2V > >+#ifdef CONFIG_THUMB2_KERNEL >+#define HAVE_ARCH_MODULE_KALLSYMS_SYMBOL_VALUE >+static inline unsigned long module_kallsyms_symbol_value(const Elf_Sym *sym) >+{ >+ if (ELF_ST_TYPE(sym->st_info) == STT_FUNC) >+ return sym->st_value & ~1; >+ >+ return sym->st_value; >+} >+#endif >+ > #endif /* _ASM_ARM_MODULE_H */ >diff --git a/include/linux/module.h b/include/linux/module.h >index fce6b4335e36..12146257eb5d 100644 >--- a/include/linux/module.h >+++ b/include/linux/module.h >@@ -486,6 +486,13 @@ struct module { > #define MODULE_ARCH_INIT {} > #endif > >+#ifndef HAVE_ARCH_MODULE_KALLSYMS_SYMBOL_VALUE >+static inline unsigned long module_kallsyms_symbol_value(const Elf_Sym *sym) >+{ >+ return sym->st_value; >+} >+#endif >+ > extern struct mutex module_mutex; > > /* FIXME: It'd be nice to isolate modules during init, too, so they >diff --git a/kernel/module.c b/kernel/module.c >index 3d86a38b580c..9364017fdc21 100644 >--- a/kernel/module.c >+++ b/kernel/module.c >@@ -3922,7 +3922,7 @@ static const char *get_ksymbol(struct module *mod, > unsigned long *offset) > { > unsigned int i, best = 0; >- unsigned long nextval; >+ unsigned long nextval, bestval; > struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); > > /* At worse, next value is at end of module */ >@@ -3931,10 +3931,15 @@ static const char *get_ksymbol(struct module *mod, > else > nextval = (unsigned long)mod->core_layout.base+mod->core_layout.text_size; > >+ bestval = module_kallsyms_symbol_value(&kallsyms->symtab[best]); >+ > /* Scan for closest preceding symbol, and next symbol. (ELF > starts real symbols at 1). */ > for (i = 1; i < kallsyms->num_symtab; i++) { >- if (kallsyms->symtab[i].st_shndx == SHN_UNDEF) >+ const Elf_Sym *sym = &kallsyms->symtab[i]; >+ unsigned long thisval = module_kallsyms_symbol_value(sym); >+ >+ if (sym->st_shndx == SHN_UNDEF) > continue; > > /* We ignore unnamed symbols: they're uninformative >@@ -3943,21 +3948,21 @@ static const char *get_ksymbol(struct module *mod, > || is_arm_mapping_symbol(symname(kallsyms, i))) > continue; > >- if (kallsyms->symtab[i].st_value <= addr >- && kallsyms->symtab[i].st_value > kallsyms->symtab[best].st_value) >+ if (thisval <= addr && thisval > bestval) { > best = i; >- if (kallsyms->symtab[i].st_value > addr >- && kallsyms->symtab[i].st_value < nextval) >- nextval = kallsyms->symtab[i].st_value; >+ bestval = thisval; >+ } >+ if (thisval > addr && thisval < nextval) >+ nextval = thisval; > } > > if (!best) > return NULL; > > if (size) >- *size = nextval - kallsyms->symtab[best].st_value; >+ *size = nextval - bestval; > if (offset) >- *offset = addr - kallsyms->symtab[best].st_value; >+ *offset = addr - bestval; > return symname(kallsyms, best); > } > >@@ -4060,8 +4065,10 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, > continue; > kallsyms = rcu_dereference_sched(mod->kallsyms); > if (symnum < kallsyms->num_symtab) { >- *value = kallsyms->symtab[symnum].st_value; >- *type = kallsyms->symtab[symnum].st_size; >+ const Elf_Sym *sym = &kallsyms->symtab[symnum]; >+ >+ *value = module_kallsyms_symbol_value(sym); >+ *type = sym->st_size; > strlcpy(name, symname(kallsyms, symnum), KSYM_NAME_LEN); > strlcpy(module_name, mod->name, MODULE_NAME_LEN); > *exported = is_exported(name, *value, mod); >@@ -4079,10 +4086,13 @@ static unsigned long mod_find_symname(struct module *mod, const char *name) > unsigned int i; > struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); > >- for (i = 0; i < kallsyms->num_symtab; i++) >+ for (i = 0; i < kallsyms->num_symtab; i++) { >+ const Elf_Sym *sym = &kallsyms->symtab[i]; >+ > if (strcmp(name, symname(kallsyms, i)) == 0 && >- kallsyms->symtab[i].st_shndx != SHN_UNDEF) >- return kallsyms->symtab[i].st_value; >+ sym->st_shndx != SHN_UNDEF) >+ return module_kallsyms_symbol_value(sym); >+ } > return 0; > } > >@@ -4127,12 +4137,13 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, > if (mod->state == MODULE_STATE_UNFORMED) > continue; > for (i = 0; i < kallsyms->num_symtab; i++) { >+ const Elf_Sym *sym = &kallsyms->symtab[i]; > >- if (kallsyms->symtab[i].st_shndx == SHN_UNDEF) >+ if (sym->st_shndx == SHN_UNDEF) > continue; > >- ret = fn(data, symname(kallsyms, i), >- mod, kallsyms->symtab[i].st_value); >+ ret = fn(data, symname(kallsyms, i), mod, >+ module_kallsyms_symbol_value(sym)); > if (ret != 0) > return ret; > } >-- >2.11.0 >
On Thu, Dec 06, 2018 at 06:29:20PM +0100, Jessica Yu wrote: > Also, do you mind if I drop the module_ prefix from > module_kallsyms_symbol_value()? I recently submitted some internal > module kallsyms cleanups [1] and there we have the newly renamed > kallsyms_symbol_name(), so I think it'd be nice if we kept the naming > scheme consistent with just kallsyms_symbol_value(). I could just do > this myself if you don't want to respin a v6. I've sent out a v6 with this change. I also rebased the change on top of your cleanups in modules-next. Thanks.
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h index 9e81b7c498d8..c7bcf0347801 100644 --- a/arch/arm/include/asm/module.h +++ b/arch/arm/include/asm/module.h @@ -61,4 +61,15 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val); MODULE_ARCH_VERMAGIC_ARMTHUMB \ MODULE_ARCH_VERMAGIC_P2V +#ifdef CONFIG_THUMB2_KERNEL +#define HAVE_ARCH_MODULE_KALLSYMS_SYMBOL_VALUE +static inline unsigned long module_kallsyms_symbol_value(const Elf_Sym *sym) +{ + if (ELF_ST_TYPE(sym->st_info) == STT_FUNC) + return sym->st_value & ~1; + + return sym->st_value; +} +#endif + #endif /* _ASM_ARM_MODULE_H */ diff --git a/include/linux/module.h b/include/linux/module.h index fce6b4335e36..12146257eb5d 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -486,6 +486,13 @@ struct module { #define MODULE_ARCH_INIT {} #endif +#ifndef HAVE_ARCH_MODULE_KALLSYMS_SYMBOL_VALUE +static inline unsigned long module_kallsyms_symbol_value(const Elf_Sym *sym) +{ + return sym->st_value; +} +#endif + extern struct mutex module_mutex; /* FIXME: It'd be nice to isolate modules during init, too, so they diff --git a/kernel/module.c b/kernel/module.c index 3d86a38b580c..9364017fdc21 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -3922,7 +3922,7 @@ static const char *get_ksymbol(struct module *mod, unsigned long *offset) { unsigned int i, best = 0; - unsigned long nextval; + unsigned long nextval, bestval; struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); /* At worse, next value is at end of module */ @@ -3931,10 +3931,15 @@ static const char *get_ksymbol(struct module *mod, else nextval = (unsigned long)mod->core_layout.base+mod->core_layout.text_size; + bestval = module_kallsyms_symbol_value(&kallsyms->symtab[best]); + /* Scan for closest preceding symbol, and next symbol. (ELF starts real symbols at 1). */ for (i = 1; i < kallsyms->num_symtab; i++) { - if (kallsyms->symtab[i].st_shndx == SHN_UNDEF) + const Elf_Sym *sym = &kallsyms->symtab[i]; + unsigned long thisval = module_kallsyms_symbol_value(sym); + + if (sym->st_shndx == SHN_UNDEF) continue; /* We ignore unnamed symbols: they're uninformative @@ -3943,21 +3948,21 @@ static const char *get_ksymbol(struct module *mod, || is_arm_mapping_symbol(symname(kallsyms, i))) continue; - if (kallsyms->symtab[i].st_value <= addr - && kallsyms->symtab[i].st_value > kallsyms->symtab[best].st_value) + if (thisval <= addr && thisval > bestval) { best = i; - if (kallsyms->symtab[i].st_value > addr - && kallsyms->symtab[i].st_value < nextval) - nextval = kallsyms->symtab[i].st_value; + bestval = thisval; + } + if (thisval > addr && thisval < nextval) + nextval = thisval; } if (!best) return NULL; if (size) - *size = nextval - kallsyms->symtab[best].st_value; + *size = nextval - bestval; if (offset) - *offset = addr - kallsyms->symtab[best].st_value; + *offset = addr - bestval; return symname(kallsyms, best); } @@ -4060,8 +4065,10 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, continue; kallsyms = rcu_dereference_sched(mod->kallsyms); if (symnum < kallsyms->num_symtab) { - *value = kallsyms->symtab[symnum].st_value; - *type = kallsyms->symtab[symnum].st_size; + const Elf_Sym *sym = &kallsyms->symtab[symnum]; + + *value = module_kallsyms_symbol_value(sym); + *type = sym->st_size; strlcpy(name, symname(kallsyms, symnum), KSYM_NAME_LEN); strlcpy(module_name, mod->name, MODULE_NAME_LEN); *exported = is_exported(name, *value, mod); @@ -4079,10 +4086,13 @@ static unsigned long mod_find_symname(struct module *mod, const char *name) unsigned int i; struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); - for (i = 0; i < kallsyms->num_symtab; i++) + for (i = 0; i < kallsyms->num_symtab; i++) { + const Elf_Sym *sym = &kallsyms->symtab[i]; + if (strcmp(name, symname(kallsyms, i)) == 0 && - kallsyms->symtab[i].st_shndx != SHN_UNDEF) - return kallsyms->symtab[i].st_value; + sym->st_shndx != SHN_UNDEF) + return module_kallsyms_symbol_value(sym); + } return 0; } @@ -4127,12 +4137,13 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, if (mod->state == MODULE_STATE_UNFORMED) continue; for (i = 0; i < kallsyms->num_symtab; i++) { + const Elf_Sym *sym = &kallsyms->symtab[i]; - if (kallsyms->symtab[i].st_shndx == SHN_UNDEF) + if (sym->st_shndx == SHN_UNDEF) continue; - ret = fn(data, symname(kallsyms, i), - mod, kallsyms->symtab[i].st_value); + ret = fn(data, symname(kallsyms, i), mod, + module_kallsyms_symbol_value(sym)); if (ret != 0) return ret; }
Thumb-2 functions have the lowest bit set in the symbol value in the symtab. When kallsyms are generated for the vmlinux, the kallsyms are generated from the output of nm, and nm clears the lowest bit. $ arm-linux-gnueabihf-readelf -a vmlinux | grep show_interrupts 95947: 8015dc89 686 FUNC GLOBAL DEFAULT 2 show_interrupts $ arm-linux-gnueabihf-nm vmlinux | grep show_interrupts 8015dc88 T show_interrupts $ cat /proc/kallsyms | grep show_interrupts 8015dc88 T show_interrupts However, for modules, the kallsyms uses the values in the symbol table without modification, so for functions in modules, the lowest bit is set in kallsyms. $ arm-linux-gnueabihf-readelf -a drivers/net/tun.ko | grep tun_get_socket 333: 00002d4d 36 FUNC GLOBAL DEFAULT 1 tun_get_socket $ arm-linux-gnueabihf-nm drivers/net/tun.ko | grep tun_get_socket 00002d4c T tun_get_socket $ cat /proc/kallsyms | grep tun_get_socket 7f802d4d t tun_get_socket [tun] Because of this, the symbol+offset of the crashing instruction shown in oopses is incorrect when the crash is in a module. For example, given a tun_get_socket which starts like this, 00002d4c <tun_get_socket>: 2d4c: 6943 ldr r3, [r0, #20] 2d4e: 4a07 ldr r2, [pc, #28] 2d50: 4293 cmp r3, r2 a crash when tun_get_socket is called with NULL results in: PC is at tun_xdp+0xa3/0xa4 [tun] pc : [<7f802d4c>] As can be seen, the "PC is at" line reports the wrong symbol name, and the symbol+offset will point to the wrong source line if it is passed to gdb. To solve this, add a way for archs to fixup the reading of these module kallsyms values, and use that to clear the lowest bit for function symbols on Thumb-2. After the fix: # cat /proc/kallsyms | grep tun_get_socket 7f802d4c t tun_get_socket [tun] PC is at tun_get_socket+0x0/0x24 [tun] pc : [<7f802d4c>] Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> --- v5: Use/move local variables to reduce calls and keep lines short. Use const arg. v4: Split out st_value overwrite change. Add HAVE* macro to avoid function call. v3: Do not overwrite st_value v2: Fix build warning with !MODULES arch/arm/include/asm/module.h | 11 +++++++++++ include/linux/module.h | 7 +++++++ kernel/module.c | 45 +++++++++++++++++++++++++++---------------- 3 files changed, 46 insertions(+), 17 deletions(-)