linux-kernel - Re: [PATCH] x86/umip: Fix insn_get_code_seg

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Date:   Mon, 27 Nov 2017 19:56:35 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...gle.com>,
        Nick Desaulniers <nick.desaulniers@...il.com>
Subject: Re: [PATCH] x86/umip: Fix insn_get_code_seg_params()'s return value

On Thu, Nov 23, 2017 at 10:19:51AM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> In order to save on redundant structs definitions
> insn_get_code_seg_params() was made to return two 4-bit values in a char
> but clang complains:
> 
>   arch/x86/lib/insn-eval.c:780:10: warning: implicit conversion from 'int' to 'char'
> 	  changes value from 132 to -124 [-Wconstant-conversion]
>                   return INSN_CODE_SEG_PARAMS(4, 8);
>                   ~~~~~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~
>   ./arch/x86/include/asm/insn-eval.h:16:57: note: expanded from macro 'INSN_CODE_SEG_PARAMS'
>   #define INSN_CODE_SEG_PARAMS(oper_sz, addr_sz) (oper_sz | (addr_sz << 4))
> 
> Those two values do get picked apart afterwards the opposite way of how
> they were ORed so wrt to the LSByte, the return value is the same.
> 
> But this function returns -EINVAL in the error case, which is an int. So
> make it return an int which is the native word size anyway and thus fix
> the clang warning.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Reported-by: Kees Cook <keescook@...gle.com>
> Reported-by: Nick Desaulniers <nick.desaulniers@...il.com>
> Cc: ricardo.neri-calderon@...ux.intel.com

Thanks Kees and Nick for finding this bug. Thanks Borislav for the quick fix!
This change looks OK to me.

BR,
Ricardo