[PATCH v4 1/3] arm64: Add macro version of the BTI instruction

Mark Brown
2021-12-14T15:29:30Z

BTI is only available from v8.5 so we need to encode it using HINT in
generic code and for older toolchains. Add an assembler macro based on
one written by Mark Rutland which lets us use the mnemonic and update
the existing users.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/crypto/aes-modes.S | 10 +++++-----
arch/arm64/include/asm/assembler.h | 10 ++++++++++
arch/arm64/include/asm/linkage.h | 7 +------
3 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S
index b495de22bb38..ff01f0167ba2 100644
--- a/arch/arm64/crypto/aes-modes.S
+++ b/arch/arm64/crypto/aes-modes.S
@@ -363,15 +363,15 @@ ST5( mov v4.16b, vctr.16b )
adr x16, 1f
sub x16, x16, x12, lsl #3
br x16
- hint 34 // bti c
+ bti c
mov v0.d[0], vctr.d[0]
- hint 34 // bti c
+ bti c
mov v1.d[0], vctr.d[0]
- hint 34 // bti c
+ bti c
mov v2.d[0], vctr.d[0]
- hint 34 // bti c
+ bti c
mov v3.d[0], vctr.d[0]
-ST5( hint 34 )
+ST5( bti c )
ST5( mov v4.d[0], vctr.d[0] )
1: b 2f
.previous
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 136d13f3d6e9..e8bd0af0141c 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -790,6 +790,16 @@ alternative_endif
.Lnoyield_\@:
.endm

+/*
+ * Branch Target Identifier (BTI)
+ */
+ .macro bti, targets
+ .equ .L__bti_targets_c, 34
+ .equ .L__bti_targets_j, 36
+ .equ .L__bti_targets_jc,38
+ hint #.L__bti_targets_\targets
+ .endm
+
/*
* This macro emits a program property note section identifying
* architecture features which require special handling, mainly for
diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index 9906541a6861..c5d0c11d7709 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h
@@ -6,12 +6,7 @@

#if defined(CONFIG_ARM64_BTI_KERNEL) && defined(__aarch64__)

-/*
- * Since current versions of gas reject the BTI instruction unless we
- * set the architecture version to v8.5 we use the hint instruction
- * instead.
- */
-#define BTI_C hint 34 ;
+#define BTI_C bti c ;

/*
* When using in-kernel BTI we need to ensure that PCS-conformant assembly