linux-kernel - Re: [PATCH] x86/e820: fix the function type for e820__mapped

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Date:   Fri, 27 Nov 2020 13:15:26 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH] x86/e820: fix the function type for e820__mapped_all

On Fri, Nov 13, 2020 at 10:26:54AM -0800, Sami Tolvanen wrote:
> e820__mapped_all is passed as a callback to is_mmconf_reserved, which
> expects a function of type:
> 
>   typedef bool (*check_reserved_t)(u64 start, u64 end, unsigned type);
> 
> This trips indirect call checking with Clang's Control-Flow Integrity
> (CFI). Change the last argument from enum e820_type to unsigned to fix
> the type mismatch.
> 
> Reported-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
>  arch/x86/include/asm/e820/api.h | 2 +-
>  arch/x86/kernel/e820.c          | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/e820/api.h b/arch/x86/include/asm/e820/api.h
> index e8f58ddd06d9..e872a796619d 100644
> --- a/arch/x86/include/asm/e820/api.h
> +++ b/arch/x86/include/asm/e820/api.h
> @@ -12,7 +12,7 @@ extern unsigned long pci_mem_start;
>  
>  extern bool e820__mapped_raw_any(u64 start, u64 end, enum e820_type type);
>  extern bool e820__mapped_any(u64 start, u64 end, enum e820_type type);
> -extern bool e820__mapped_all(u64 start, u64 end, enum e820_type type);
> +extern bool e820__mapped_all(u64 start, u64 end, unsigned type);

I think the proper fix is to fix the typedef to:

	typedef bool (*check_reserved_t)(u64 start, u64 end, enum e820_type type);

because

* is_mmconf_reserved() is passing in E820_TYPE_RESERVED which is enum e820_type

* is_acpi_reserved() is the other check_reserved_t function ptr and the last arg
type there is unused so it can just as well be enum e820_type.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette