2021-05-21 20:08:49

by Marco Elver

Subject: [PATCH] init: verify that function is initcall_t at compile-time

In the spirit of making it hard to misuse an interface, add a
compile-time assertion in the CONFIG_HAVE_ARCH_PREL32_RELOCATIONS case
to verify the initcall function matches initcall_t, because the inline
asm bypasses any type-checking the compiler would otherwise do. This
will help developers catch incorrect API use in all configurations.

A recent example of this is:
https://lkml.kernel.org/r/[email protected]

Signed-off-by: Marco Elver <[email protected]>
Reviewed-by: Miguel Ojeda <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
---
include/linux/init.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index 045ad1650ed1..d82b4b2e1d25 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -242,7 +242,8 @@ extern bool initcall_debug;
asm(".section \"" __sec "\", \"a\" \n" \
__stringify(__name) ": \n" \
".long " __stringify(__stub) " - . \n" \
- ".previous \n");
+ ".previous \n"); \
+ static_assert(__same_type(initcall_t, &fn));
#else
#define ____define_initcall(fn, __unused, __name, __sec) \
static initcall_t __name __used \
--
2.31.1.818.g46aad6cb9e-goog

2021-05-21 20:22:13

by Sami Tolvanen

Subject: Re: [PATCH] init: verify that function is initcall_t at compile-time

Hi Marco,

On Fri, May 21, 2021 at 12:26 AM Marco Elver <[email protected]> wrote:
>
> In the spirit of making it hard to misuse an interface, add a
> compile-time assertion in the CONFIG_HAVE_ARCH_PREL32_RELOCATIONS case
> to verify the initcall function matches initcall_t, because the inline
> asm bypasses any type-checking the compiler would otherwise do. This
> will help developers catch incorrect API use in all configurations.
>
> A recent example of this is:
> https://lkml.kernel.org/r/[email protected]
>
> Signed-off-by: Marco Elver <[email protected]>
> Reviewed-by: Miguel Ojeda <[email protected]>
> Reviewed-by: Nathan Chancellor <[email protected]>
> Tested-by: Nathan Chancellor <[email protected]>
> ---
> include/linux/init.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 045ad1650ed1..d82b4b2e1d25 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -242,7 +242,8 @@ extern bool initcall_debug;
> asm(".section \"" __sec "\", \"a\" \n" \
> __stringify(__name) ": \n" \
> ".long " __stringify(__stub) " - . \n" \
> - ".previous \n");
> + ".previous \n"); \
> + static_assert(__same_type(initcall_t, &fn));
> #else
> #define ____define_initcall(fn, __unused, __name, __sec) \
> static initcall_t __name __used \

This looks like a nice improvement, thank you for sending the patch!

Reviewed-by: Sami Tolvanen <[email protected]>

Sami

2021-05-21 20:24:11

by Paul E. McKenney

Subject: Re: [PATCH] init: verify that function is initcall_t at compile-time

On Fri, May 21, 2021 at 09:26:10AM +0200, Marco Elver wrote:
> In the spirit of making it hard to misuse an interface, add a
> compile-time assertion in the CONFIG_HAVE_ARCH_PREL32_RELOCATIONS case
> to verify the initcall function matches initcall_t, because the inline
> asm bypasses any type-checking the compiler would otherwise do. This
> will help developers catch incorrect API use in all configurations.
>
> A recent example of this is:
> https://lkml.kernel.org/r/[email protected]
>
> Signed-off-by: Marco Elver <[email protected]>
> Reviewed-by: Miguel Ojeda <[email protected]>
> Reviewed-by: Nathan Chancellor <[email protected]>
> Tested-by: Nathan Chancellor <[email protected]>

Tested-by: Paul E. McKenney <[email protected]>

> ---
> include/linux/init.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 045ad1650ed1..d82b4b2e1d25 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -242,7 +242,8 @@ extern bool initcall_debug;
> asm(".section \"" __sec "\", \"a\" \n" \
> __stringify(__name) ": \n" \
> ".long " __stringify(__stub) " - . \n" \
> - ".previous \n");
> + ".previous \n"); \
> + static_assert(__same_type(initcall_t, &fn));
> #else
> #define ____define_initcall(fn, __unused, __name, __sec) \
> static initcall_t __name __used \
> --
> 2.31.1.818.g46aad6cb9e-goog
>

2021-05-21 20:25:51

by Kees Cook

Subject: Re: [PATCH] init: verify that function is initcall_t at compile-time

On Fri, 21 May 2021 09:26:10 +0200, Marco Elver wrote:
> In the spirit of making it hard to misuse an interface, add a
> compile-time assertion in the CONFIG_HAVE_ARCH_PREL32_RELOCATIONS case
> to verify the initcall function matches initcall_t, because the inline
> asm bypasses any type-checking the compiler would otherwise do. This
> will help developers catch incorrect API use in all configurations.
>
> A recent example of this is:
> https://lkml.kernel.org/r/[email protected]

Since this touches on CFI, I've taken this patch.

Applied to for-next/clang/features, thanks!

[1/1] init: verify that function is initcall_t at compile-time
https://git.kernel.org/kees/c/72a12a91a634

--
Kees Cook