Re: regrename/i386: ROP vs df and stack-regs

[Bernd Schmidt <bschmidt@redhat.com>]

On 11/27/2015 10:02 AM, Bernd Schmidt wrote:
> This is a patch for PRs 68471 and 68472, which show problems with the
> ROP mitigation:
>   * reg-stack doesn't call df_insn_update when it makes changes, and
>     if df checking is enabled, any subsequent df_analyze call will
>     abort
>   * Using -mcmodel=medium fails because of a pattern that has lea type
>     and needs its modrm_class overridden.
>
> Both of these are fixed in the i386 backend. As a further safety
> measure, I've added some extra code to regrename to ignore stack regs
> after regstack_complete - they can't be dealt with anymore.
>
> Bootstrapped and tested on x86_64-linux, with -mmitigate-rop forced on. Ok?

> 	PR target/68471
> 	PR target/68472
> 	* config/i386/i386.c (ix86_mitigate_rop): Don't call
> 	compute_bb_for_insn again.  Call df_insn_rescan_all.
> 	* config/i386/i386.md (set_got_rex64): Override modrm_class.
>
> 	* regrename.c (build_def_use): Ignore stack regs if regstack_completed.
>
> testsuite/
> 	* gcc.target/i386/rop1.c: New test.
>
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index 2ac6c25..14c99eb 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -45243,8 +45243,9 @@ ix86_mitigate_rop (void)
>    COPY_HARD_REG_SET (inout_risky, input_risky);
>    IOR_HARD_REG_SET (inout_risky, output_risky);
>
> -  compute_bb_for_insn ();
>    df_note_add_problem ();
> +  /* Fix up what stack-regs did.  */
> +  df_insn_rescan_all ();
>    df_analyze ();
>
>    regrename_init (true);
> diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
> index a57d165..671580d 100644
> --- a/gcc/config/i386/i386.md
> +++ b/gcc/config/i386/i386.md
> @@ -12418,6 +12418,7 @@
>    "lea{q}\t{_GLOBAL_OFFSET_TABLE_(%%rip), %0|%0, _GLOBAL_OFFSET_TABLE_[rip]}"
>    [(set_attr "type" "lea")
>     (set_attr "length_address" "4")
> +   (set_attr "modrm_class" "unknown")
>     (set_attr "mode" "DI")])
>
>  (define_insn "set_rip_rex64"
> --- /dev/null	2015-11-23 12:05:22.553607702 +0100
> +++ gcc/testsuite/gcc.target/i386/rop1.c	2015-11-24 15:40:04.381086953 +0100
> @@ -0,0 +1,7 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target lp64 } */
> +/* { dg-options "-mcmodel=medium -mmitigate-rop" } */
> +void
> +foo (void)
> +{
> +}

Ccing Uros for the i386 bits.


Bernd