Richard Earnshaw via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
[...]
>> Thanks for the reviews.
>> Add -mbranch-protection option. This option enables the
>> code-generation of
>> pointer signing and authentication instructions in function prologues and
>> epilogues.
>> 2021-10-25 Tejas Belagod <tbela...@arm.com>
>> gcc/ChangeLog:
>> * config/arm/arm.c (arm_configure_build_target): Parse and
>> validate
>> -mbranch-protection option and initialize appropriate data structures.
>> * config/arm/arm.opt: New option -mbranch-protection.
>
> .../arm.opt (-mbranch-protection) : New option.
>
>> * doc/invoke.texi: Document -mbranch-protection.
>
> .../invoke.texi (Arm Options): Document it.
>
>> Tested the following configurations, OK for trunk?
>> -mthumb/-march=armv8.1-m.main+pacbti/-mfloat-abi=soft
>> -marm/-march=armv7-a/-mfpu=vfpv3-d16/-mfloat-abi=softfp
>> mcmodel=small and tiny
>> aarch64-none-linux-gnu native test and bootstrap
>>
>
> +@item
> -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}][+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]
> +@opindex mbranch-protection
> +Select the branch protection features to use.
> +@samp{none} is the default and turns off all types of branch protection.
> +@samp{standard} turns on all types of branch protection features. If
> a feature
> +has additional tuning options, then @samp{standard} sets it to its standard
> +level.
> +@samp{pac-ret[+@var{leaf}]} turns on return address signing to its standard
> +level: signing functions that save the return address to memory (non-leaf
> +functions will practically always do this). The optional argument
> @samp{leaf}
> +can be used to extend the signing to include leaf functions.
> +@samp{bti} turns on branch target identification mechanism.
>
> This doesn't really use the right documentation style. Closer would be:
[...]
Hi Richard,
thanks for reviewing, here is the updated patch.
Best Regards
Andrea
>From 3383a1e265b7b695c5d6ce6115ad66eed2a4cb48 Mon Sep 17 00:00:00 2001
From: Andrea Corallo <andrea.cora...@arm.com>
Date: Mon, 6 Dec 2021 11:39:03 +0100
Subject: [PATCH] Add option -mbranch-protection.
Add -mbranch-protection option. This option enables the
code-generation of pointer signing and authentication instructions in
function prologues and epilogues.
gcc/ChangeLog:
* config/arm/arm.c (arm_configure_build_target): Parse and validate
-mbranch-protection option and initialize appropriate data structures.
* config/arm/arm.opt (-mbranch-protection): New option.
* doc/invoke.texi (Arm Options): Document it.
Co-Authored-By: Tejas Belagod <tbela...@arm.com>
Co-Authored-By: Richard Earnshaw <richard.earns...@arm.com>
---
gcc/config/arm/arm.c | 11 +++++++++++
gcc/config/arm/arm.opt | 4 ++++
gcc/doc/invoke.texi | 35 +++++++++++++++++++++++++++++++++--
3 files changed, 48 insertions(+), 2 deletions(-)
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 96186b8ad02..ee22acddee5 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -3237,6 +3237,17 @@ arm_configure_build_target (struct arm_build_target
*target,
tune_opts = strchr (opts->x_arm_tune_string, '+');
}
+ if (opts->x_arm_branch_protection_string)
+ {
+ aarch_validate_mbranch_protection (opts->x_arm_branch_protection_string);
+
+ if (aarch_ra_sign_key != AARCH_KEY_A)
+ {
+ warning (0, "invalid key type for %<-mbranch-protection=%>");
+ aarch_ra_sign_key = AARCH_KEY_A;
+ }
+ }
+
if (arm_selected_arch)
{
arm_initialize_isa (target->isa, arm_selected_arch->common.isa_bits);
diff --git a/gcc/config/arm/arm.opt b/gcc/config/arm/arm.opt
index 5c5b4f3ae06..4f2754c3e84 100644
--- a/gcc/config/arm/arm.opt
+++ b/gcc/config/arm/arm.opt
@@ -313,6 +313,10 @@ mbranch-cost=
Target RejectNegative Joined UInteger Var(arm_branch_cost) Init(-1)
Cost to assume for a branch insn.
+mbranch-protection=
+Target RejectNegative Joined Var(arm_branch_protection_string) Save
+Use branch-protection features.
+
mgeneral-regs-only
Target RejectNegative Mask(GENERAL_REGS_ONLY) Save
Generate code which uses the core registers only (r0-r14).
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 3257df5596d..a808c6bb599 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -820,7 +820,9 @@ Objective-C and Objective-C++ Dialects}.
-mpure-code @gol
-mcmse @gol
-mfix-cmse-cve-2021-35465 @gol
--mfdpic}
+-mfdpic @gol
+-mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}]
+[+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]}
@emph{AVR Options}
@gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol
@@ -21187,7 +21189,36 @@ The opposite @option{-mno-fdpic} option is useful (and
required) to
build the Linux kernel using the same (@code{arm-*-uclinuxfdpiceabi})
toolchain as the one used to build the userland programs.
-@end table
+@item
+-mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}][+@var{bti}]|@var{bti}[+@var{pac-ret}[+@var{leaf}]]
+@opindex mbranch-protection
+Enable branch protection features (armv8.1-m.main only).
+@samp{none} generate code without branch protection or return address
+signing.
+@samp{standard[+@var{leaf}]} generate code with all branch protection
+features enabled at their standard level.
+@samp{pac-ret[+@var{leaf}]} generate code with return address signing
+set to its standard level, which is to sign all functions that save
+the return address to memory.
+@samp{leaf} When return address signing is enabled, also sign leaf
+functions even if they do not write the return address to memory.
++@samp{bti} Add landing-pad instructions at the permitted targets of
+indirect branch instructions.
+
+If the @samp{+pacbti} architecture extension is not enabled, then all
+branch protection and return address signing operations are
+constrained to use only the instructions defined in the
+architectural-NOP space. The generated code will remain
+backwards-compatible with earlier versions of the architecture, but
+the additional security can be enabled at run time on processors that
+support the @samp{PACBTI} extension.
+
+Branch target enforcement using BTI can only be enabled at runtime if
+all code in the application has been compiled with at least
+@samp{-mbranch-protection=bti}.
+
+The default is to generate code without branch protection or return
+address signing.
@node AVR Options
@subsection AVR Options
--
2.20.1
