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

[Ricardo Neri]

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@xxxxxxx>
> > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > Cc: Adam Buchbinder <adam.buchbinder@xxxxxxxxx>
> > Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> > Cc: Qiaowei Ren <qiaowei.ren@xxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Nathan Howard <liverlint@xxxxxxxxx>
> > Cc: Adan Hawthorn <adanhawthorn@xxxxxxxxx>
> > Cc: Joe Perches <joe@xxxxxxxxxxx>
> > Cc: Ravi V. Shankar <ravi.v.shankar@xxxxxxxxx>
> > Cc: x86@xxxxxxxxxx
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> > ---
> >  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