Re: [PATCH] x86: Document -mno-cet-switch

[Uros Bizjak <ubizjak@gmail.com>]

On Tue, May 10, 2022 at 6:20 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> When -fcf-protection=branch is used, the compiler will generate jump
> tables where the indirect jump is prefixed with the NOTRACK prefix, so
> it can jump to non-ENDBR targets. Yet, for NOTRACK prefixes to work, the
> NOTRACK specific enable bit must be set, what renders the binary broken
> on any environment where this is not the case. In fact, having NOTRACK
> disabled was a design choice for the Linux kernel CET support.
>
> Generate jump tables with ENDBR and skip the NOTRACK prefix for indirect
> jump.  Document -mno-cet-switch to turn off CET instrumentation on jump
> tables for switch statements.
>
> gcc/
>
>         PR target/104816
>         * config/i386/i386.opt: Turn on -mcet-switch by default.
>         * doc/invoke.texi: Document -mno-cet-switch.
>
> gcc/testsuite/
>
>         * gcc.target/i386/cet-switch-1.c: Add -mno-cet-switch.
>         * gcc.target/i386/cet-switch-2.c: Remove -mcet-switch.
>         * gcc.target/i386/cet-switch-3.c: Likewise.

LGTM.

Thanks,
Uros.

> ---
>  gcc/config/i386/i386.opt                     | 2 +-
>  gcc/doc/invoke.texi                          | 9 ++++++++-
>  gcc/testsuite/gcc.target/i386/cet-switch-1.c | 2 +-
>  gcc/testsuite/gcc.target/i386/cet-switch-2.c | 2 +-
>  gcc/testsuite/gcc.target/i386/cet-switch-3.c | 2 +-
>  5 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> index a6b0e28f238..96b4a433e44 100644
> --- a/gcc/config/i386/i386.opt
> +++ b/gcc/config/i386/i386.opt
> @@ -1047,7 +1047,7 @@ Enable shadow stack built-in functions from Control-flow Enforcement
>  Technology (CET).
>
>  mcet-switch
> -Target Undocumented Var(flag_cet_switch) Init(0)
> +Target Var(flag_cet_switch) Init(1)
>  Turn on CET instrumentation for switch statements that use a jump table and
>  an indirect jump.
>
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 7a35d9613a4..8bb96c5938a 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -1420,7 +1420,8 @@ See RS/6000 and PowerPC Options.
>  -msse4a  -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4  -mxop @gol
>  -madx  -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mhle  -mlwp @gol
>  -mmwaitx  -mclzero  -mpku  -mthreads  -mgfni  -mvaes  -mwaitpkg @gol
> --mshstk -mmanual-endbr -mforce-indirect-call  -mavx512vbmi2 -mavx512bf16 -menqcmd @gol
> +-mshstk -mmanual-endbr -mno-cet-switch -mforce-indirect-call @gol
> +-mavx512vbmi2 -mavx512bf16 -menqcmd @gol
>  -mvpclmulqdq  -mavx512bitalg  -mmovdiri  -mmovdir64b  -mavx512vpopcntdq @gol
>  -mavx5124fmaps  -mavx512vnni  -mavx5124vnniw  -mprfchw  -mrdpid @gol
>  -mrdseed  -msgx -mavx512vp2intersect -mserialize -mtsxldtrk@gol
> @@ -32641,6 +32642,12 @@ function attribute. This is useful when used with the option
>  @option{-fcf-protection=branch} to control ENDBR insertion at the
>  function entry.
>
> +@item -mno-cet-switch
> +@opindex mno-cet-switch
> +@opindex mcet-switch
> +Turn off CET instrumentation for switch statements that use a jump table
> +and an indirect jump.  The default is @option{mcet-switch}.
> +
>  @item -mcall-ms2sysv-xlogues
>  @opindex mcall-ms2sysv-xlogues
>  @opindex mno-call-ms2sysv-xlogues
> diff --git a/gcc/testsuite/gcc.target/i386/cet-switch-1.c b/gcc/testsuite/gcc.target/i386/cet-switch-1.c
> index afe5adc2f3d..4931c3ad1d2 100644
> --- a/gcc/testsuite/gcc.target/i386/cet-switch-1.c
> +++ b/gcc/testsuite/gcc.target/i386/cet-switch-1.c
> @@ -1,6 +1,6 @@
>  /* Verify that CET works.  */
>  /* { dg-do compile } */
> -/* { dg-options "-O -fcf-protection" } */
> +/* { dg-options "-O -fcf-protection -mno-cet-switch" } */
>  /* { dg-final { scan-assembler-times "endbr32" 1 { target ia32 } } } */
>  /* { dg-final { scan-assembler-times "endbr64" 1 { target { ! ia32 } } } } */
>  /* { dg-final { scan-assembler-times "notrack jmp\[ \t]+\[*]" 1 } } */
> diff --git a/gcc/testsuite/gcc.target/i386/cet-switch-2.c b/gcc/testsuite/gcc.target/i386/cet-switch-2.c
> index 69ddc6fd5b7..11578d1a30c 100644
> --- a/gcc/testsuite/gcc.target/i386/cet-switch-2.c
> +++ b/gcc/testsuite/gcc.target/i386/cet-switch-2.c
> @@ -1,6 +1,6 @@
>  /* Verify that CET works.  */
>  /* { dg-do compile } */
> -/* { dg-options "-O -fcf-protection -mcet-switch" } */
> +/* { dg-options "-O -fcf-protection" } */
>  /* { dg-final { scan-assembler-times "endbr32" 12 { target ia32 } } } */
>  /* { dg-final { scan-assembler-times "endbr64" 12 { target { ! ia32 } } } } */
>  /* { dg-final { scan-assembler-times "\[ \t]+jmp\[ \t]+\[*]" 1 } } */
> diff --git a/gcc/testsuite/gcc.target/i386/cet-switch-3.c b/gcc/testsuite/gcc.target/i386/cet-switch-3.c
> index 0d9ed4488dd..a4e2e4dfc16 100644
> --- a/gcc/testsuite/gcc.target/i386/cet-switch-3.c
> +++ b/gcc/testsuite/gcc.target/i386/cet-switch-3.c
> @@ -1,6 +1,6 @@
>  /* Verify that CET works.  */
>  /* { dg-do compile } */
> -/* { dg-options "-O -fcf-protection -mcet-switch" } */
> +/* { dg-options "-O -fcf-protection" } */
>  /* { dg-final { scan-assembler-times "endbr32" 12 { target ia32 } } } */
>  /* { dg-final { scan-assembler-times "endbr64" 12 { target { ! ia32 } } } } */
>  /* { dg-final { scan-assembler-times "\[ \t]+jmp\[ \t]+\[*]" 1 } } */
> --
> 2.35.1
>