diff mbox series

[v2,04/17] module: ensure __cfi_check alignment

Message ID 20210318171111.706303-5-samitolvanen@google.com (mailing list archive)
State Superseded
Headers show
Series Add support for Clang CFI | expand

Commit Message

Sami Tolvanen March 18, 2021, 5:10 p.m. UTC
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(-)

Comments

Nick Desaulniers March 18, 2021, 7:27 p.m. UTC | #1
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
>
Sami Tolvanen March 18, 2021, 9:43 p.m. UTC | #2
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 mbox series

Patch

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 */