| Message ID | 20210914191045.2234020-5-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | x86: Add support for Clang CFI | expand |
On Tue, Sep 14, 2021 at 12:10 PM Sami Tolvanen <samitolvanen@google.com> wrote: > > This change introduces the DEFINE_CFI_IMMEDIATE_RETURN_STUB macro, > which defines a stub function that immediately returns and when > defined in the core kernel, always passes indirect call checking > with CONFIG_CFI_CLANG. Note that this macro should only be used when > a stub cannot be called using the correct function type. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > include/asm-generic/vmlinux.lds.h | 11 +++++++++++ > include/linux/cfi.h | 14 ++++++++++++++ > kernel/cfi.c | 24 +++++++++++++++++++++++- > 3 files changed, 48 insertions(+), 1 deletion(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index f2984af2b85b..5b77284f7221 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -407,6 +407,16 @@ > KEEP(*(.static_call_tramp_key)) \ > __stop_static_call_tramp_key = .; > > +#ifdef CONFIG_CFI_CLANG > +#define CFI_EXCLUDED_DATA \ > + . = ALIGN(8); \ > + __start_cfi_excluded = .; \ > + KEEP(*(.cfi_excluded_stubs)) \ > + __stop_cfi_excluded = .; > +#else > +#define CFI_EXCLUDED_DATA > +#endif > + > /* > * Allow architectures to handle ro_after_init data on their > * own by defining an empty RO_AFTER_INIT_DATA. > @@ -430,6 +440,7 @@ > __start_rodata = .; \ > *(.rodata) *(.rodata.*) \ > SCHED_DATA \ > + CFI_EXCLUDED_DATA \ > RO_AFTER_INIT_DATA /* Read only after init */ \ > . = ALIGN(8); \ > __start___tracepoints_ptrs = .; \ > diff --git a/include/linux/cfi.h b/include/linux/cfi.h > index 879744aaa6e0..9ebf67a0d421 100644 > --- a/include/linux/cfi.h > +++ b/include/linux/cfi.h > @@ -20,6 +20,18 @@ extern void __cfi_check(uint64_t id, void *ptr, void *diag); > #define __CFI_ADDRESSABLE(fn, __attr) \ > const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn > > +/* > + * Defines a stub function that returns immediately, and when defined and > + * referenced in the core kernel, always passes CFI checking. This should > + * be used only for stubs that cannot be called using the correct function > + * pointer type, which should be rare. > + */ > +#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \ > + void fn(void) { return; } \ > + const void *__cfi_excl_ ## fn __visible \ > + __attribute__((__section__(".cfi_excluded_stubs"))) \ Can we use __section from include/linux/compiler_attributes.h here rather than open coding the function attribute? > + = (void *)&fn > + > #ifdef CONFIG_CFI_CLANG_SHADOW > > extern void cfi_module_add(struct module *mod, unsigned long base_addr); > @@ -35,6 +47,8 @@ static inline void cfi_module_remove(struct module *mod, unsigned long base_addr > #else /* !CONFIG_CFI_CLANG */ > > #define __CFI_ADDRESSABLE(fn, __attr) > +#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \ > + void fn(void) { return; } > > #endif /* CONFIG_CFI_CLANG */ > > diff --git a/kernel/cfi.c b/kernel/cfi.c > index 9594cfd1cf2c..8d931089141b 100644 > --- a/kernel/cfi.c > +++ b/kernel/cfi.c > @@ -278,12 +278,34 @@ static inline cfi_check_fn find_module_check_fn(unsigned long ptr) > return fn; > } > > +extern unsigned long __start_cfi_excluded[]; > +extern unsigned long __stop_cfi_excluded[]; > + > +static inline bool is_cfi_excluded(unsigned long ptr) > +{ > + unsigned long *p = __start_cfi_excluded; > + > + for ( ; p < __stop_cfi_excluded; ++p) > + if (*p == ptr) > + return true; > + > + return false; > +} > + > +static void __cfi_pass(uint64_t id, void *ptr, void *diag) > +{ > +} > + > static inline cfi_check_fn find_check_fn(unsigned long ptr) > { > cfi_check_fn fn = NULL; > > - if (is_kernel_text(ptr)) > + if (is_kernel_text(ptr)) { > + if (unlikely(is_cfi_excluded(ptr))) > + return __cfi_pass; > + > return __cfi_check; > + } > > /* > * Indirect call checks can happen when RCU is not watching. Both > -- > 2.33.0.309.g3052b89438-goog >
On Tue, Sep 14, 2021 at 12:36 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Tue, Sep 14, 2021 at 12:10 PM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > This change introduces the DEFINE_CFI_IMMEDIATE_RETURN_STUB macro, > > which defines a stub function that immediately returns and when > > defined in the core kernel, always passes indirect call checking > > with CONFIG_CFI_CLANG. Note that this macro should only be used when > > a stub cannot be called using the correct function type. > > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > > --- > > include/asm-generic/vmlinux.lds.h | 11 +++++++++++ > > include/linux/cfi.h | 14 ++++++++++++++ > > kernel/cfi.c | 24 +++++++++++++++++++++++- > > 3 files changed, 48 insertions(+), 1 deletion(-) > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index f2984af2b85b..5b77284f7221 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -407,6 +407,16 @@ > > KEEP(*(.static_call_tramp_key)) \ > > __stop_static_call_tramp_key = .; > > > > +#ifdef CONFIG_CFI_CLANG > > +#define CFI_EXCLUDED_DATA \ > > + . = ALIGN(8); \ > > + __start_cfi_excluded = .; \ > > + KEEP(*(.cfi_excluded_stubs)) \ > > + __stop_cfi_excluded = .; > > +#else > > +#define CFI_EXCLUDED_DATA > > +#endif > > + > > /* > > * Allow architectures to handle ro_after_init data on their > > * own by defining an empty RO_AFTER_INIT_DATA. > > @@ -430,6 +440,7 @@ > > __start_rodata = .; \ > > *(.rodata) *(.rodata.*) \ > > SCHED_DATA \ > > + CFI_EXCLUDED_DATA \ > > RO_AFTER_INIT_DATA /* Read only after init */ \ > > . = ALIGN(8); \ > > __start___tracepoints_ptrs = .; \ > > diff --git a/include/linux/cfi.h b/include/linux/cfi.h > > index 879744aaa6e0..9ebf67a0d421 100644 > > --- a/include/linux/cfi.h > > +++ b/include/linux/cfi.h > > @@ -20,6 +20,18 @@ extern void __cfi_check(uint64_t id, void *ptr, void *diag); > > #define __CFI_ADDRESSABLE(fn, __attr) \ > > const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn > > > > +/* > > + * Defines a stub function that returns immediately, and when defined and > > + * referenced in the core kernel, always passes CFI checking. This should > > + * be used only for stubs that cannot be called using the correct function > > + * pointer type, which should be rare. > > + */ > > +#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \ > > + void fn(void) { return; } \ > > + const void *__cfi_excl_ ## fn __visible \ > > + __attribute__((__section__(".cfi_excluded_stubs"))) \ > > Can we use __section from include/linux/compiler_attributes.h here > rather than open coding the function attribute? Sure. I'll change this in v4. Sami
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index f2984af2b85b..5b77284f7221 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -407,6 +407,16 @@ KEEP(*(.static_call_tramp_key)) \ __stop_static_call_tramp_key = .; +#ifdef CONFIG_CFI_CLANG +#define CFI_EXCLUDED_DATA \ + . = ALIGN(8); \ + __start_cfi_excluded = .; \ + KEEP(*(.cfi_excluded_stubs)) \ + __stop_cfi_excluded = .; +#else +#define CFI_EXCLUDED_DATA +#endif + /* * Allow architectures to handle ro_after_init data on their * own by defining an empty RO_AFTER_INIT_DATA. @@ -430,6 +440,7 @@ __start_rodata = .; \ *(.rodata) *(.rodata.*) \ SCHED_DATA \ + CFI_EXCLUDED_DATA \ RO_AFTER_INIT_DATA /* Read only after init */ \ . = ALIGN(8); \ __start___tracepoints_ptrs = .; \ diff --git a/include/linux/cfi.h b/include/linux/cfi.h index 879744aaa6e0..9ebf67a0d421 100644 --- a/include/linux/cfi.h +++ b/include/linux/cfi.h @@ -20,6 +20,18 @@ extern void __cfi_check(uint64_t id, void *ptr, void *diag); #define __CFI_ADDRESSABLE(fn, __attr) \ const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn +/* + * Defines a stub function that returns immediately, and when defined and + * referenced in the core kernel, always passes CFI checking. This should + * be used only for stubs that cannot be called using the correct function + * pointer type, which should be rare. + */ +#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \ + void fn(void) { return; } \ + const void *__cfi_excl_ ## fn __visible \ + __attribute__((__section__(".cfi_excluded_stubs"))) \ + = (void *)&fn + #ifdef CONFIG_CFI_CLANG_SHADOW extern void cfi_module_add(struct module *mod, unsigned long base_addr); @@ -35,6 +47,8 @@ static inline void cfi_module_remove(struct module *mod, unsigned long base_addr #else /* !CONFIG_CFI_CLANG */ #define __CFI_ADDRESSABLE(fn, __attr) +#define DEFINE_CFI_IMMEDIATE_RETURN_STUB(fn) \ + void fn(void) { return; } #endif /* CONFIG_CFI_CLANG */ diff --git a/kernel/cfi.c b/kernel/cfi.c index 9594cfd1cf2c..8d931089141b 100644 --- a/kernel/cfi.c +++ b/kernel/cfi.c @@ -278,12 +278,34 @@ static inline cfi_check_fn find_module_check_fn(unsigned long ptr) return fn; } +extern unsigned long __start_cfi_excluded[]; +extern unsigned long __stop_cfi_excluded[]; + +static inline bool is_cfi_excluded(unsigned long ptr) +{ + unsigned long *p = __start_cfi_excluded; + + for ( ; p < __stop_cfi_excluded; ++p) + if (*p == ptr) + return true; + + return false; +} + +static void __cfi_pass(uint64_t id, void *ptr, void *diag) +{ +} + static inline cfi_check_fn find_check_fn(unsigned long ptr) { cfi_check_fn fn = NULL; - if (is_kernel_text(ptr)) + if (is_kernel_text(ptr)) { + if (unlikely(is_cfi_excluded(ptr))) + return __cfi_pass; + return __cfi_check; + } /* * Indirect call checks can happen when RCU is not watching. Both
This change introduces the DEFINE_CFI_IMMEDIATE_RETURN_STUB macro, which defines a stub function that immediately returns and when defined in the core kernel, always passes indirect call checking with CONFIG_CFI_CLANG. Note that this macro should only be used when a stub cannot be called using the correct function type. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- include/asm-generic/vmlinux.lds.h | 11 +++++++++++ include/linux/cfi.h | 14 ++++++++++++++ kernel/cfi.c | 24 +++++++++++++++++++++++- 3 files changed, 48 insertions(+), 1 deletion(-)