linux-kernel - Re: [PATCH v9 16/29] x86/insn-eval: Add function to get default params of code segment

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Date:   Thu, 12 Oct 2017 11:27:15 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Adam Buchbinder <adam.buchbinder@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v9 16/29] x86/insn-eval: Add function to get default
 params of code segment

On Thu, 2017-10-12 at 18:31 +0200, Borislav Petkov wrote:
> On Tue, Oct 03, 2017 at 08:54:19PM -0700, Ricardo Neri wrote:
> > 
> > Obtain the default values of the address and operand sizes as specified in
> > the D and L bits of the the segment descriptor selected by the register
> > CS. The function can be used for both protected and long modes.
> > For virtual-8086 mode, the default address and operand sizes are always 2
> > bytes.
> > 
> > The returned parameters are encoded in a signed 8-bit data type. Auxiliar
> > macros are provided to encode and decode such values.
> > 
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Cc: Adam Buchbinder <adam.buchbinder@...il.com>
> > Cc: Colin Ian King <colin.king@...onical.com>
> > Cc: Lorenzo Stoakes <lstoakes@...il.com>
> > Cc: Qiaowei Ren <qiaowei.ren@...el.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Cc: Masami Hiramatsu <mhiramat@...nel.org>
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Thomas Garnier <thgarnie@...gle.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Borislav Petkov <bp@...e.de>
> > Cc: Dmitry Vyukov <dvyukov@...gle.com>
> > Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
> > Cc: x86@...nel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> > ---
> >  arch/x86/include/asm/insn-eval.h |  5 ++++
> >  arch/x86/lib/insn-eval.c         | 64
> > ++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 69 insertions(+)
> Some cleanups ontop:
> 
> ---
> diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
> index 64924b7d5fff..3352b9d5164f 100644
> --- a/arch/x86/lib/insn-eval.c
> +++ b/arch/x86/lib/insn-eval.c
> @@ -614,14 +614,14 @@ static unsigned long get_seg_limit(struct pt_regs *regs,
> int seg_reg_idx)
>  }
>  
>  /**
> - * insn_get_code_seg_defaults() - Obtain code segment default parameters
> + * insn_get_code_seg_params() - Obtain code segment parameters
>   * @regs:	Structure with register values as seen when entering kernel
> mode
>   *
> - * Obtain the default parameters of the code segment: address and operand
> sizes.
> - * The code segment is obtained from the selector contained in the CS
> register
> - * in regs. In protected mode, the default address is determined by
> inspecting
> - * the L and D bits of the segment descriptor. In virtual-8086 mode, the
> default
> - * is always two bytes for both address and operand sizes.
> + * Obtain address and operand sizes of the code segment. It is obtained from
> the
> + * selector contained in the CS register in regs. In protected mode, the
> default
> + * address is determined by inspecting the L and D bits of the segment
> descriptor.
> + * In virtual-8086 mode, the default is always two bytes for both address and
> + * operand sizes.
>   *
>   * Returns:
>   *
> @@ -629,7 +629,7 @@ static unsigned long get_seg_limit(struct pt_regs *regs,
> int seg_reg_idx)
>   *
>   * -EINVAL on error.
>   */
> -char insn_get_code_seg_defaults(struct pt_regs *regs)
> +char insn_get_code_seg_params(struct pt_regs *regs)
>  {
>  	struct desc_struct *desc;
>  	short sel;
> @@ -640,7 +640,7 @@ char insn_get_code_seg_defaults(struct pt_regs *regs)
>  
>  	sel = get_segment_selector(regs, INAT_SEG_REG_CS);
>  	if (sel < 0)
> -		return -1L;
> +		return sel;

Thanks! I implemente these changes along with your Improvements-by.

BR,
Ricardo