| Message ID | 20210318171111.706303-5-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for Clang CFI | expand |
On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > CONFIG_CFI_CLANG_SHADOW assumes the __cfi_check() function is page > aligned and at the beginning of the .text section. While Clang would > normally align the function correctly, it fails to do so for modules > with no executable code. > > This change ensures the correct __cfi_check() location and > alignment. It also discards the .eh_frame section, which Clang can > generate with certain sanitizers, such as CFI. > > Link: https://bugs.llvm.org/show_bug.cgi?id=46293 > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > scripts/module.lds.S | 18 +++++++++++++++++- > 1 file changed, 17 insertions(+), 1 deletion(-) > > diff --git a/scripts/module.lds.S b/scripts/module.lds.S > index 168cd27e6122..93518579cf5d 100644 > --- a/scripts/module.lds.S > +++ b/scripts/module.lds.S > @@ -3,10 +3,19 @@ > * Archs are free to supply their own linker scripts. ld will > * combine them automatically. > */ > +#include <asm/page.h> > + > +#ifdef CONFIG_CFI_CLANG > +# define ALIGN_CFI ALIGN(PAGE_SIZE) > +#else > +# define ALIGN_CFI > +#endif > + > SECTIONS { > /DISCARD/ : { > *(.discard) > *(.discard.*) > + *(.eh_frame) Do we want to unconditionally discard this section from modules for all arches/configs? I like how we conditionally do so on SANITIZER_DISCARDS in include/asm-generic/vmlinux.lds.h for example. > } > > __ksymtab 0 : { *(SORT(___ksymtab+*)) } > @@ -40,7 +49,14 @@ SECTIONS { > *(.rodata..L*) > } > > - .text : { *(.text .text.[0-9a-zA-Z_]*) } > + /* > + * With CONFIG_CFI_CLANG, we assume __cfi_check is at the beginning > + * of the .text section, and is aligned to PAGE_SIZE. > + */ > + .text : ALIGN_CFI { > + *(.text.__cfi_check) > + *(.text .text.[0-9a-zA-Z_]* .text..L.cfi*) > + } > } > > /* bring in arch-specific sections */ > -- > 2.31.0.291.g576ba9dcdaf-goog >
On Thu, Mar 18, 2021 at 12:27 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > CONFIG_CFI_CLANG_SHADOW assumes the __cfi_check() function is page > > aligned and at the beginning of the .text section. While Clang would > > normally align the function correctly, it fails to do so for modules > > with no executable code. > > > > This change ensures the correct __cfi_check() location and > > alignment. It also discards the .eh_frame section, which Clang can > > generate with certain sanitizers, such as CFI. > > > > Link: https://bugs.llvm.org/show_bug.cgi?id=46293 > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > > --- > > scripts/module.lds.S | 18 +++++++++++++++++- > > 1 file changed, 17 insertions(+), 1 deletion(-) > > > > diff --git a/scripts/module.lds.S b/scripts/module.lds.S > > index 168cd27e6122..93518579cf5d 100644 > > --- a/scripts/module.lds.S > > +++ b/scripts/module.lds.S > > @@ -3,10 +3,19 @@ > > * Archs are free to supply their own linker scripts. ld will > > * combine them automatically. > > */ > > +#include <asm/page.h> > > + > > +#ifdef CONFIG_CFI_CLANG > > +# define ALIGN_CFI ALIGN(PAGE_SIZE) > > +#else > > +# define ALIGN_CFI > > +#endif > > + > > SECTIONS { > > /DISCARD/ : { > > *(.discard) > > *(.discard.*) > > + *(.eh_frame) > > Do we want to unconditionally discard this section from modules for > all arches/configs? I like how we conditionally do so on > SANITIZER_DISCARDS in include/asm-generic/vmlinux.lds.h for example. I think nothing should generate this section unless one of the sanitizers is enabled, but I'm fine with using the same logic as vmlinux.lds.h here. I'll change this in v3. Sami
diff --git a/scripts/module.lds.S b/scripts/module.lds.S index 168cd27e6122..93518579cf5d 100644 --- a/scripts/module.lds.S +++ b/scripts/module.lds.S @@ -3,10 +3,19 @@ * Archs are free to supply their own linker scripts. ld will * combine them automatically. */ +#include <asm/page.h> + +#ifdef CONFIG_CFI_CLANG +# define ALIGN_CFI ALIGN(PAGE_SIZE) +#else +# define ALIGN_CFI +#endif + SECTIONS { /DISCARD/ : { *(.discard) *(.discard.*) + *(.eh_frame) } __ksymtab 0 : { *(SORT(___ksymtab+*)) } @@ -40,7 +49,14 @@ SECTIONS { *(.rodata..L*) } - .text : { *(.text .text.[0-9a-zA-Z_]*) } + /* + * With CONFIG_CFI_CLANG, we assume __cfi_check is at the beginning + * of the .text section, and is aligned to PAGE_SIZE. + */ + .text : ALIGN_CFI { + *(.text.__cfi_check) + *(.text .text.[0-9a-zA-Z_]* .text..L.cfi*) + } } /* bring in arch-specific sections */
CONFIG_CFI_CLANG_SHADOW assumes the __cfi_check() function is page aligned and at the beginning of the .text section. While Clang would normally align the function correctly, it fails to do so for modules with no executable code. This change ensures the correct __cfi_check() location and alignment. It also discards the .eh_frame section, which Clang can generate with certain sanitizers, such as CFI. Link: https://bugs.llvm.org/show_bug.cgi?id=46293 Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- scripts/module.lds.S | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)