linux-kernel - Re: [PATCH v8 05/28] x86/mpx: Use signed variables to compute effective addresses

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Message-ID: <1504153154.51857.15.camel@ranerica-desktop>
Date:   Wed, 30 Aug 2017 21:19:14 -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>,
        Liang Z Li <liang.z.li@...el.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>,
        Nathan Howard <liverlint@...il.com>,
        Adan Hawthorn <adanhawthorn@...il.com>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v8 05/28] x86/mpx: Use signed variables to compute
 effective addresses

On Tue, 2017-08-29 at 18:09 +0200, Borislav Petkov wrote:
> On Fri, Aug 18, 2017 at 05:27:46PM -0700, Ricardo Neri wrote:
> > Even though memory addresses are unsigned, the operands used to compute the
> > effective address do have a sign. This is true for ModRM.rm, SIB.base,
> > SIB.index as well as the displacement bytes. Thus, signed variables shall
> > be used when computing the effective address from these operands. Once the
> > signed effective address has been computed, it is casted to an unsigned
> > long to determine the linear address.
> > 
> > Variables are renamed to better reflect the type of address being
> > computed.
> > 
> > Cc: Borislav Petkov <bp@...e.de>
> > Cc: Andy Lutomirski <luto@...nel.org>
> > 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: Peter Zijlstra <peterz@...radead.org>
> > Cc: Nathan Howard <liverlint@...il.com>
> > Cc: Adan Hawthorn <adanhawthorn@...il.com>
> > Cc: Joe Perches <joe@...ches.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/mm/mpx.c | 20 ++++++++++++++------
> >  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> I think you can simplify this function even more (diff ontop):
> 
> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
> index 9eec98022510..d0ec5c9b2a57 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -139,7 +139,7 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
>  static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
>  {
>  	int addr_offset, base_offset, indx_offset;
> -	unsigned long linear_addr;
> +	unsigned long linear_addr = -1;
>  	long eff_addr, base, indx;
>  	insn_byte_t sib;
>  
> @@ -150,18 +150,18 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
>  	if (X86_MODRM_MOD(insn->modrm.value) == 3) {
>  		addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
>  		if (addr_offset < 0)
> -			goto out_err;
> +			goto out;
>  
>  		eff_addr = regs_get_register(regs, addr_offset);
>  	} else {
>  		if (insn->sib.nbytes) {
>  			base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
>  			if (base_offset < 0)
> -				goto out_err;
> +				goto out;
>  This is a good suggestion. This is a good suggestion. 
>  			indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
>  			if (indx_offset < 0)
> -				goto out_err;
> +				goto out;
>  
>  			base = regs_get_register(regs, base_offset);
>  			indx = regs_get_register(regs, indx_offset);
> @@ -170,7 +170,7 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
>  		} else {
>  			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
>  			if (addr_offset < 0)
> -				goto out_err;
> +				goto out;
>  
>  			eff_addr = regs_get_register(regs, addr_offset);
>  		}
> @@ -180,9 +180,8 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
>  
>  	linear_addr = (unsigned long)eff_addr;
>  
> +out:
>  	return (void __user *)linear_addr;
> -out_err:
> -	return (void __user *)-1;

This is a good suggestion. I will work on it. By now my series comprises
28 patches. If you plan to review the rest of the series and you don't
have major objections, could I work on these updates as increments from
my v8 series? I think that with 28 patches in the series is becoming
difficult to review.

Thanks and BR,
Ricardo