| Message ID | 20170218055844.1457-2-ewk@edkovsky.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 17 Feb 2017 21:58:42 -0800 "Eddie Kovsky" <ewk@edkovsky.org> wrote: > Implement a mechanism to check if a module's address is in > the rodata or ro_after_init sections. It mimics the exsiting functions > that test if an address is inside a module's text section. > > Signed-off-by: Eddie Kovsky <ewk@edkovsky.org> I don't see the point of this for many of the hyper-v functions. They are only called from a small number of places, and this can be validated by code inspection. Adding this seems just seems to be code bloat to me.
On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger <stephen@networkplumber.org> wrote: > On Fri, 17 Feb 2017 21:58:42 -0800 > "Eddie Kovsky" <ewk@edkovsky.org> wrote: > >> Implement a mechanism to check if a module's address is in >> the rodata or ro_after_init sections. It mimics the exsiting functions >> that test if an address is inside a module's text section. >> >> Signed-off-by: Eddie Kovsky <ewk@edkovsky.org> > > I don't see the point of this for many of the hyper-v functions. > They are only called from a small number of places, and this can be validated > by code inspection. Adding this seems just seems to be code bloat to me. I think it has value in that it effectively blocks any way for non-ro_after_init structures from being passed into these functions. Since there are so few callers now, it's the perfect place to add this. -Kees
On Tue, 21 Feb 2017 12:32:16 -0800 Kees Cook <keescook@chromium.org> wrote: > On Mon, Feb 20, 2017 at 9:14 AM, Stephen Hemminger > <stephen@networkplumber.org> wrote: > > On Fri, 17 Feb 2017 21:58:42 -0800 > > "Eddie Kovsky" <ewk@edkovsky.org> wrote: > > > >> Implement a mechanism to check if a module's address is in > >> the rodata or ro_after_init sections. It mimics the exsiting functions > >> that test if an address is inside a module's text section. > >> > >> Signed-off-by: Eddie Kovsky <ewk@edkovsky.org> > > > > I don't see the point of this for many of the hyper-v functions. > > They are only called from a small number of places, and this can be validated > > by code inspection. Adding this seems just seems to be code bloat to me. > > I think it has value in that it effectively blocks any way for > non-ro_after_init structures from being passed into these functions. > Since there are so few callers now, it's the perfect place to add > this. > > -Kees > Maybe for a more used API, but for such a corner case it is code bloat.
+++ Eddie Kovsky [17/02/17 22:58 -0700]: >Implement a mechanism to check if a module's address is in >the rodata or ro_after_init sections. It mimics the exsiting functions >that test if an address is inside a module's text section. It would be helpful to explain in the changelog the motivation or reason we're adding to the current api, and why this is needed. >Signed-off-by: Eddie Kovsky <ewk@edkovsky.org> >--- > include/linux/module.h | 7 +++++++ > kernel/module.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 51 insertions(+) > >diff --git a/include/linux/module.h b/include/linux/module.h >index 0297c5cd7cdf..1608d3570ee2 100644 >--- a/include/linux/module.h >+++ b/include/linux/module.h >@@ -492,7 +492,9 @@ static inline int module_is_live(struct module *mod) > > struct module *__module_text_address(unsigned long addr); > struct module *__module_address(unsigned long addr); >+struct module *__module_ro_address(unsigned long addr); > bool is_module_address(unsigned long addr); >+bool is_module_ro_address(unsigned long addr); > bool is_module_percpu_address(unsigned long addr); > bool is_module_text_address(unsigned long addr); > >@@ -645,6 +647,11 @@ static inline struct module *__module_address(unsigned long addr) > return NULL; > } > >+static inline struct module *__module_ro_address(unsigned long addr) >+{ >+ return NULL; >+} >+ There needs to be a corresponding !CONFIG_MODULES stub for is_module_ro_address() as well, see is_module_address(), etc. > static inline struct module *__module_text_address(unsigned long addr) > { > return NULL; >diff --git a/kernel/module.c b/kernel/module.c >index 7eba6dea4f41..298cfe4645b1 100644 >--- a/kernel/module.c >+++ b/kernel/module.c >@@ -4275,6 +4275,50 @@ struct module *__module_text_address(unsigned long addr) > } > EXPORT_SYMBOL_GPL(__module_text_address); > >+/** >+ * is_module_text_ro_address - is this address inside read-only module code? >+ * @addr: the address to check. s/is_module_text_ro_address/is_module_ro_address/ Although I would slightly prefer the name is_module_rodata_address, or something similar, because it's unclear to me (without looking at the code) whether the function covers text addresses. And we already have is_module_text_address() for that case. >+ * >+ */ >+bool is_module_ro_address(unsigned long addr) >+{ >+ bool ret; >+ >+ preempt_disable(); >+ ret = __module_ro_address(addr) != NULL; >+ preempt_enable(); >+ >+ return ret; >+} >+ >+/* >+ * __module_ro_address - get the module whose code contains a read-only address. Maybe we should be more specific in the comment and clarify that we're getting the module whose rodata/ro_after_init sections contain the given address. >+ * @addr: the address. >+ * >+ * Must be called with preempt disabled or module mutex held so that >+ * module doesn't get freed during this. >+ */ >+struct module *__module_ro_address(unsigned long addr) >+{ >+ struct module *mod = __module_address(addr); >+ >+ if (mod) { >+ /* Make sure it's within the read-only section. */ >+ if (!within(addr, mod->init_layout.base, >+ mod->init_layout.ro_size) >+ && !within(addr, mod->core_layout.base, >+ mod->core_layout.ro_size)) >+ mod = NULL; If a ro_after_init address gets passed in here, mod will be prematurely set to NULL here, because it is not within [base, base + ro_size). See comment above frob_text() in module.c for a module layout "diagram". Also, starting from layout.base will give us the text region as well, but we just want to check the rodata/ro_after_init regions, same as what the kernel counterpart in patch 2/3 does. The rodata region starts at base + text_size. So we can just simplify this to just one conditional: (ugly, but shouldn't look bad when cleaned up with some variables) if (!within(addr, mod->init_layout.base + mod->init_layout.text_size, mod->init_layout.ro_after_init_size - mod->init_layout.text_size) && !within(addr, mod->core_layout.base + mod->core_layout.text_size, mod->core_layout.ro_after_init_size - mod->core_layout.text_size)) This is because range [base + text_size, base + ro_after_init_size) encompasses both the rodata and ro_after_init regions. Jessica >+ if (!within(addr, mod->init_layout.base, >+ mod->init_layout.ro_after_init_size) >+ && !within(addr, mod->core_layout.base, >+ mod->core_layout.ro_after_init_size)) >+ mod = NULL; >+ } >+ return mod; >+} >+EXPORT_SYMBOL_GPL(__module_ro_address); >+ > /* Don't grab lock, we're oopsing. */ > void print_modules(void) > { >-- >2.11.1
diff --git a/include/linux/module.h b/include/linux/module.h index 0297c5cd7cdf..1608d3570ee2 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -492,7 +492,9 @@ static inline int module_is_live(struct module *mod) struct module *__module_text_address(unsigned long addr); struct module *__module_address(unsigned long addr); +struct module *__module_ro_address(unsigned long addr); bool is_module_address(unsigned long addr); +bool is_module_ro_address(unsigned long addr); bool is_module_percpu_address(unsigned long addr); bool is_module_text_address(unsigned long addr); @@ -645,6 +647,11 @@ static inline struct module *__module_address(unsigned long addr) return NULL; } +static inline struct module *__module_ro_address(unsigned long addr) +{ + return NULL; +} + static inline struct module *__module_text_address(unsigned long addr) { return NULL; diff --git a/kernel/module.c b/kernel/module.c index 7eba6dea4f41..298cfe4645b1 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -4275,6 +4275,50 @@ struct module *__module_text_address(unsigned long addr) } EXPORT_SYMBOL_GPL(__module_text_address); +/** + * is_module_text_ro_address - is this address inside read-only module code? + * @addr: the address to check. + * + */ +bool is_module_ro_address(unsigned long addr) +{ + bool ret; + + preempt_disable(); + ret = __module_ro_address(addr) != NULL; + preempt_enable(); + + return ret; +} + +/* + * __module_ro_address - get the module whose code contains a read-only address. + * @addr: the address. + * + * Must be called with preempt disabled or module mutex held so that + * module doesn't get freed during this. + */ +struct module *__module_ro_address(unsigned long addr) +{ + struct module *mod = __module_address(addr); + + if (mod) { + /* Make sure it's within the read-only section. */ + if (!within(addr, mod->init_layout.base, + mod->init_layout.ro_size) + && !within(addr, mod->core_layout.base, + mod->core_layout.ro_size)) + mod = NULL; + if (!within(addr, mod->init_layout.base, + mod->init_layout.ro_after_init_size) + && !within(addr, mod->core_layout.base, + mod->core_layout.ro_after_init_size)) + mod = NULL; + } + return mod; +} +EXPORT_SYMBOL_GPL(__module_ro_address); + /* Don't grab lock, we're oopsing. */ void print_modules(void) {
Implement a mechanism to check if a module's address is in the rodata or ro_after_init sections. It mimics the exsiting functions that test if an address is inside a module's text section. Signed-off-by: Eddie Kovsky <ewk@edkovsky.org> --- include/linux/module.h | 7 +++++++ kernel/module.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) -- 2.11.1