linux-kernel - Re: [PATCH v10 19/20] x86/asm/efi: Create a stack frame in efi

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Date:	Fri, 14 Aug 2015 10:11:59 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	Chris J Arges <chris.j.arges@...onical.com>,
	live-patching@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v10 19/20] x86/asm/efi: Create a stack frame in efi_call()

On Thu, 13 Aug, at 10:10:40PM, Josh Poimboeuf wrote:
> efi_call() is a callable non-leaf function which doesn't honor
> CONFIG_FRAME_POINTER, which can result in bad stack traces.
> 
> Create a stack frame for it when CONFIG_FRAME_POINTER is enabled.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Matt Fleming <matt.fleming@...el.com>
> ---
>  arch/x86/platform/efi/efi_stub_64.S | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/platform/efi/efi_stub_64.S b/arch/x86/platform/efi/efi_stub_64.S
> index 86d0f9e..0df2dcc 100644
> --- a/arch/x86/platform/efi/efi_stub_64.S
> +++ b/arch/x86/platform/efi/efi_stub_64.S
> @@ -11,6 +11,7 @@
>  #include <asm/msr.h>
>  #include <asm/processor-flags.h>
>  #include <asm/page_types.h>
> +#include <asm/frame.h>
>  
>  #define SAVE_XMM			\
>  	mov %rsp, %rax;			\
> @@ -74,6 +75,7 @@
>  	.endm
>  
>  ENTRY(efi_call)
> +	FRAME_BEGIN
>  	SAVE_XMM
>  	mov (%rsp), %rax
>  	mov 8(%rax), %rax
> @@ -88,6 +90,7 @@ ENTRY(efi_call)
>  	RESTORE_PGT
>  	addq $48, %rsp
>  	RESTORE_XMM
> +	FRAME_END
>  	ret
>  ENDPROC(efi_call)

You mention that stackvalidate will recursively validate the frame
pointers in all code paths. Since we're calling into firmware code from
efi_call(), we don't need to do anything special here right?

I'm guessing stackvalidate would just stop since it has no way of
knowing the target address of the %call instruction, but I just wanted
to check (especially since the firmware ABI is different).

Reviewed-by: Matt Fleming <matt.fleming@...el.com>

-- 
Matt Fleming, Intel Open Source Technology Center
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