2024-01-22 18:55:04

by Samuel Holland

Subject: [PATCH] scs: add CONFIG_MMU dependency for vfree_atomic()

The shadow call stack implementation fails to build without CONFIG_MMU:

ld.lld: error: undefined symbol: vfree_atomic
>>> referenced by scs.c
>>> kernel/scs.o:(scs_free) in archive vmlinux.a

Fixes: a2abe7cbd8fe ("scs: switch to vmapped shadow stacks")
Signed-off-by: Samuel Holland <[email protected]>
---

arch/Kconfig | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index c91917b50873..a5af0edd3eb8 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -673,6 +673,7 @@ config SHADOW_CALL_STACK
bool "Shadow Call Stack"
depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
+ depends on MMU
help
This option enables the compiler's Shadow Call Stack, which
uses a shadow stack to protect function return addresses from
--
2.43.0

2024-01-22 19:54:59

by Sami Tolvanen

Subject: Re: [PATCH] scs: add CONFIG_MMU dependency for vfree_atomic()

Hi Samuel,

On Mon, Jan 22, 2024 at 9:52 AM Samuel Holland
<[email protected]> wrote:
>
> The shadow call stack implementation fails to build without CONFIG_MMU:
>
> ld.lld: error: undefined symbol: vfree_atomic
> >>> referenced by scs.c
> >>> kernel/scs.o:(scs_free) in archive vmlinux.a
>
> Fixes: a2abe7cbd8fe ("scs: switch to vmapped shadow stacks")
> Signed-off-by: Samuel Holland <[email protected]>
> ---
>
> arch/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index c91917b50873..a5af0edd3eb8 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -673,6 +673,7 @@ config SHADOW_CALL_STACK
> bool "Shadow Call Stack"
> depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
> + depends on MMU
> help
> This option enables the compiler's Shadow Call Stack, which
> uses a shadow stack to protect function return addresses from

Looks good to me. Thanks for the patch!

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

Sami

2024-01-26 16:21:24

by Christoph Hellwig

Subject: Re: [PATCH] scs: add CONFIG_MMU dependency for vfree_atomic()

On Mon, Jan 22, 2024 at 09:52:01AM -0800, Samuel Holland wrote:
> The shadow call stack implementation fails to build without CONFIG_MMU:
>
> ld.lld: error: undefined symbol: vfree_atomic
> >>> referenced by scs.c
> >>> kernel/scs.o:(scs_free) in archive vmlinux.a

Well, please just provide vfree_atomic for nommu then. vfree maps
to kfree which can be called from atomic context, so vfree_atomic
can do the same.