linux-hardening - [RFC PATCH 5/9] arm64: chacha-neon: move frame pop forward

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Date:   Wed, 13 Oct 2021 17:22:39 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-hardening@...r.kernel.org, mark.rutland@....com,
        catalin.marinas@....com, will@...nel.org,
        Ard Biesheuvel <ardb@...nel.org>
Subject: [RFC PATCH 5/9] arm64: chacha-neon: move frame pop forward

Instead of branching back to the common exit point of the routine to pop
the stack frame and return to the caller, move the frame pop to right
after the point where we last use the callee save registers. This
simplifies the generation of CFI unwind metadata, and reduces the number
of needed branches.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/crypto/chacha-neon-core.S | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/crypto/chacha-neon-core.S b/arch/arm64/crypto/chacha-neon-core.S
index b70ac76f2610..918c0beae019 100644
--- a/arch/arm64/crypto/chacha-neon-core.S
+++ b/arch/arm64/crypto/chacha-neon-core.S
@@ -691,6 +691,8 @@ CPU_BE(	  rev		a15, a15	)
 	zip2		v15.2d, v29.2d, v31.2d
 	  stp		a14, a15, [x1, #-8]
 
+	frame_pop
+
 	tbnz		x5, #63, .Lt128
 	ld1		{v28.16b-v31.16b}, [x2]
 
@@ -726,7 +728,6 @@ CPU_BE(	  rev		a15, a15	)
 	st1		{v24.16b-v27.16b}, [x1], #64
 	st1		{v28.16b-v31.16b}, [x1]
 
-.Lout:	frame_pop
 	ret
 
 	// fewer than 192 bytes of in/output
@@ -744,7 +745,7 @@ CPU_BE(	  rev		a15, a15	)
 	eor		v23.16b, v23.16b, v31.16b
 	st1		{v20.16b-v23.16b}, [x5]		// overlapping stores
 1:	st1		{v16.16b-v19.16b}, [x1]
-	b		.Lout
+	ret
 
 	// fewer than 128 bytes of in/output
 .Lt128:	ld1		{v28.16b-v31.16b}, [x10]
@@ -772,7 +773,7 @@ CPU_BE(	  rev		a15, a15	)
 	eor		v31.16b, v31.16b, v3.16b
 	st1		{v28.16b-v31.16b}, [x6]		// overlapping stores
 2:	st1		{v20.16b-v23.16b}, [x1]
-	b		.Lout
+	ret
 
 	// fewer than 320 bytes of in/output
 .Lt320:	cbz		x7, 3f				// exactly 256 bytes?
@@ -789,7 +790,7 @@ CPU_BE(	  rev		a15, a15	)
 	eor		v31.16b, v31.16b, v3.16b
 	st1		{v28.16b-v31.16b}, [x7]		// overlapping stores
 3:	st1		{v24.16b-v27.16b}, [x1]
-	b		.Lout
+	ret
 SYM_FUNC_END(chacha_4block_xor_neon)
 
 	.section	".rodata", "a", %progbits
-- 
2.30.2