Subject: Re: [for-stable-4.19 PATCH 1/2] vmlinux.lds.h: Create section for protection against instrumentation

From: Greg Kroah-Hartman <[email-masked]>
Date: Fri, 19 Mar 2021 11:39:57 +0100

On Fri, Mar 19, 2021 at 07:54:15AM +0800, Nicolas Boichat wrote:
> From: Thomas Gleixner <[email-masked]>
> 
> commit 6553896666433e7efec589838b400a2a652b3ffa upstream.
> 
> Some code pathes, especially the low level entry code, must be protected
> against instrumentation for various reasons:
> 
>  - Low level entry code can be a fragile beast, especially on x86.
> 
>  - With NO_HZ_FULL RCU state needs to be established before using it.
> 
> Having a dedicated section for such code allows to validate with tooling
> that no unsafe functions are invoked.
> 
> Add the .noinstr.text section and the noinstr attribute to mark
> functions. noinstr implies notrace. Kprobes will gain a section check
> later.
> 
> Provide also a set of markers: instrumentation_begin()/end()
> 
> These are used to mark code inside a noinstr function which calls
> into regular instrumentable text section as safe.
> 
> The instrumentation markers are only active when CONFIG_DEBUG_ENTRY is
> enabled as the end marker emits a NOP to prevent the compiler from merging
> the annotation points. This means the objtool verification requires a
> kernel compiled with this option.
> 
> Signed-off-by: Thomas Gleixner <[email-masked]>
> Reviewed-by: Alexandre Chartre <[email-masked]>
> Acked-by: Peter Zijlstra <[email-masked]>
> Link: https://lkml.kernel.org/r/[email-masked]
> 
> [Nicolas: context conflicts in:
> 	arch/powerpc/kernel/vmlinux.lds.S
> 	include/asm-generic/vmlinux.lds.h
> 	include/linux/compiler.h
> 	include/linux/compiler_types.h]
> Signed-off-by: Nicolas Boichat <[email-masked]>

Did you build this on x86?

I get the following build error:

ld:./arch/x86/kernel/vmlinux.lds:20: syntax error

And that line looks like:

 . = ALIGN(8); *(.text.hot .text.hot.*) *(.text .text.fixup) *(.text.unlikely .text.unlikely.*) *(.text.unknown .text.unknown.*) . = ALIGN(8); __noinstr_text_start = .; *(.__attribute__((noinline)) __attribute__((no_instrument_function)) __attribute((__section__(".noinstr.text"))).text) __noinstr_text_end = .; *(.text..refcount) *(.ref.text) *(.meminit.text*) *(.memexit.text*)

So I'm going to drop both of these patches from the queue.

thanks,

greg k-h