crypto: arm64/poly1305-neon - reorder PAC authentication with SP update

PAC pointer authentication signs the return address against the value
of the stack pointer, to prevent stack overrun exploits from corrupting
the control flow. However, this requires that the AUTIASP is issued with
SP holding the same value as it held when the PAC value was generated.
The Poly1305 NEON code got this wrong, resulting in crashes on PAC
capable hardware.

Fixes: f569ca16 ("crypto: arm64/poly1305 - incorporate OpenSSL/CRYPTOGAMS ...")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/poly1305-armv8.pl

@@ -840,7 +840,6 @@ poly1305_blocks_neon:
 	 ldp	d14,d15,[sp,#64]
 	addp	$ACC2,$ACC2,$ACC2
 	 ldr	x30,[sp,#8]
-	 .inst	0xd50323bf		// autiasp
 
 	////////////////////////////////////////////////////////////////
 	// lazy reduction, but without narrowing
@@ -882,6 +881,7 @@ poly1305_blocks_neon:
 	str	x4,[$ctx,#8]		// set is_base2_26
 
 	ldr	x29,[sp],#80
+	 .inst	0xd50323bf		// autiasp
 	ret
 .size	poly1305_blocks_neon,.-poly1305_blocks_neon
 

arch/arm64/crypto/poly1305-core.S_shipped

@@ -779,7 +779,6 @@ poly1305_blocks_neon:
 	 ldp	d14,d15,[sp,#64]
 	addp	v21.2d,v21.2d,v21.2d
 	 ldr	x30,[sp,#8]
-	 .inst	0xd50323bf		// autiasp
 
 	////////////////////////////////////////////////////////////////
 	// lazy reduction, but without narrowing
@@ -821,6 +820,7 @@ poly1305_blocks_neon:
 	str	x4,[x0,#8]		// set is_base2_26
 
 	ldr	x29,[sp],#80
+	 .inst	0xd50323bf		// autiasp
 	ret
 .size	poly1305_blocks_neon,.-poly1305_blocks_neon