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SubjectRe: [PATCH v8 05/28] x86/mpx: Use signed variables to compute effective addresses
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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@suse.de>
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
> > Cc: Colin Ian King <colin.king@canonical.com>
> > Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> > Cc: Qiaowei Ren <qiaowei.ren@intel.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Nathan Howard <liverlint@gmail.com>
> > Cc: Adan Hawthorn <adanhawthorn@gmail.com>
> > Cc: Joe Perches <joe@perches.com>
> > Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
> > Cc: x86@kernel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.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

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