lib/crypto: arm64/sha256: Add support for 2-way interleaved hashing

Add an implementation of sha256_finup_2x_arch() for arm64.  It
interleaves the computation of two SHA-256 hashes using the ARMv8
SHA-256 instructions.  dm-verity and fs-verity will take advantage of
this for greatly improved performance on capable CPUs.

This increases the throughput of SHA-256 hashing 4096-byte messages by
the following amounts on the following CPUs:

    ARM Cortex-X1: 70%
    ARM Cortex-X3: 68%
    ARM Cortex-A76: 65%
    ARM Cortex-A715: 43%
    ARM Cortex-A510: 25%
    ARM Cortex-A55: 8%

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250915160819.140019-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Author: Eric Biggers

lib/crypto/arm64/sha256-ce.S

@@ -70,18 +70,22 @@
 	.word		0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208
 	.word		0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
 
+	.macro load_round_constants	tmp
+	adr_l		\tmp, .Lsha2_rcon
+	ld1		{ v0.4s- v3.4s}, [\tmp], #64
+	ld1		{ v4.4s- v7.4s}, [\tmp], #64
+	ld1		{ v8.4s-v11.4s}, [\tmp], #64
+	ld1		{v12.4s-v15.4s}, [\tmp]
+	.endm
+
 	/*
 	 * size_t __sha256_ce_transform(struct sha256_block_state *state,
 	 *				const u8 *data, size_t nblocks);
 	 */
 	.text
 SYM_FUNC_START(__sha256_ce_transform)
-	/* load round constants */
-	adr_l		x8, .Lsha2_rcon
-	ld1		{ v0.4s- v3.4s}, [x8], #64
-	ld1		{ v4.4s- v7.4s}, [x8], #64
-	ld1		{ v8.4s-v11.4s}, [x8], #64
-	ld1		{v12.4s-v15.4s}, [x8]
+
+	load_round_constants	x8
 
 	/* load state */
 	ld1		{dgav.4s, dgbv.4s}, [x0]
@@ -134,3 +138,271 @@ CPU_LE(	rev32		v19.16b, v19.16b	)
 	mov		x0, x2
 	ret
 SYM_FUNC_END(__sha256_ce_transform)
+
+	.unreq dga
+	.unreq dgav
+	.unreq dgb
+	.unreq dgbv
+	.unreq t0
+	.unreq t1
+	.unreq dg0q
+	.unreq dg0v
+	.unreq dg1q
+	.unreq dg1v
+	.unreq dg2q
+	.unreq dg2v
+
+	// parameters for sha256_ce_finup2x()
+	ctx		.req	x0
+	data1		.req	x1
+	data2		.req	x2
+	len		.req	w3
+	out1		.req	x4
+	out2		.req	x5
+
+	// other scalar variables
+	count		.req	x6
+	final_step	.req	w7
+
+	// x8-x9 are used as temporaries.
+
+	// v0-v15 are used to cache the SHA-256 round constants.
+	// v16-v19 are used for the message schedule for the first message.
+	// v20-v23 are used for the message schedule for the second message.
+	// v24-v31 are used for the state and temporaries as given below.
+	// *_a are for the first message and *_b for the second.
+	state0_a_q	.req	q24
+	state0_a	.req	v24
+	state1_a_q	.req	q25
+	state1_a	.req	v25
+	state0_b_q	.req	q26
+	state0_b	.req	v26
+	state1_b_q	.req	q27
+	state1_b	.req	v27
+	t0_a		.req	v28
+	t0_b		.req	v29
+	t1_a_q		.req	q30
+	t1_a		.req	v30
+	t1_b_q		.req	q31
+	t1_b		.req	v31
+
+#define OFFSETOF_BYTECOUNT	32 // offsetof(struct __sha256_ctx, bytecount)
+#define OFFSETOF_BUF		40 // offsetof(struct __sha256_ctx, buf)
+// offsetof(struct __sha256_ctx, state) is assumed to be 0.
+
+	// Do 4 rounds of SHA-256 for each of two messages (interleaved).  m0_a
+	// and m0_b contain the current 4 message schedule words for the first
+	// and second message respectively.
+	//
+	// If not all the message schedule words have been computed yet, then
+	// this also computes 4 more message schedule words for each message.
+	// m1_a-m3_a contain the next 3 groups of 4 message schedule words for
+	// the first message, and likewise m1_b-m3_b for the second.  After
+	// consuming the current value of m0_a, this macro computes the group
+	// after m3_a and writes it to m0_a, and likewise for *_b.  This means
+	// that the next (m0_a, m1_a, m2_a, m3_a) is the current (m1_a, m2_a,
+	// m3_a, m0_a), and likewise for *_b, so the caller must cycle through
+	// the registers accordingly.
+	.macro	do_4rounds_2x	i, k,  m0_a, m1_a, m2_a, m3_a,  \
+				       m0_b, m1_b, m2_b, m3_b
+	add		t0_a\().4s, \m0_a\().4s, \k\().4s
+	add		t0_b\().4s, \m0_b\().4s, \k\().4s
+	.if \i < 48
+	sha256su0	\m0_a\().4s, \m1_a\().4s
+	sha256su0	\m0_b\().4s, \m1_b\().4s
+	sha256su1	\m0_a\().4s, \m2_a\().4s, \m3_a\().4s
+	sha256su1	\m0_b\().4s, \m2_b\().4s, \m3_b\().4s
+	.endif
+	mov		t1_a.16b, state0_a.16b
+	mov		t1_b.16b, state0_b.16b
+	sha256h		state0_a_q, state1_a_q, t0_a\().4s
+	sha256h		state0_b_q, state1_b_q, t0_b\().4s
+	sha256h2	state1_a_q, t1_a_q, t0_a\().4s
+	sha256h2	state1_b_q, t1_b_q, t0_b\().4s
+	.endm
+
+	.macro	do_16rounds_2x	i, k0, k1, k2, k3
+	do_4rounds_2x	\i + 0,  \k0,  v16, v17, v18, v19,  v20, v21, v22, v23
+	do_4rounds_2x	\i + 4,  \k1,  v17, v18, v19, v16,  v21, v22, v23, v20
+	do_4rounds_2x	\i + 8,  \k2,  v18, v19, v16, v17,  v22, v23, v20, v21
+	do_4rounds_2x	\i + 12, \k3,  v19, v16, v17, v18,  v23, v20, v21, v22
+	.endm
+
+//
+// void sha256_ce_finup2x(const struct __sha256_ctx *ctx,
+//			  const u8 *data1, const u8 *data2, int len,
+//			  u8 out1[SHA256_DIGEST_SIZE],
+//			  u8 out2[SHA256_DIGEST_SIZE]);
+//
+// This function computes the SHA-256 digests of two messages |data1| and
+// |data2| that are both |len| bytes long, starting from the initial context
+// |ctx|.  |len| must be at least SHA256_BLOCK_SIZE.
+//
+// The instructions for the two SHA-256 operations are interleaved.  On many
+// CPUs, this is almost twice as fast as hashing each message individually due
+// to taking better advantage of the CPU's SHA-256 and SIMD throughput.
+//
+SYM_FUNC_START(sha256_ce_finup2x)
+	sub		sp, sp, #128
+	mov		final_step, #0
+	load_round_constants	x8
+
+	// Load the initial state from ctx->state.
+	ld1		{state0_a.4s-state1_a.4s}, [ctx]
+
+	// Load ctx->bytecount.  Take the mod 64 of it to get the number of
+	// bytes that are buffered in ctx->buf.  Also save it in a register with
+	// len added to it.
+	ldr		x8, [ctx, #OFFSETOF_BYTECOUNT]
+	add		count, x8, len, sxtw
+	and		x8, x8, #63
+	cbz		x8, .Lfinup2x_enter_loop	// No bytes buffered?
+
+	// x8 bytes (1 to 63) are currently buffered in ctx->buf.  Load them
+	// followed by the first 64 - x8 bytes of data.  Since len >= 64, we
+	// just load 64 bytes from each of ctx->buf, data1, and data2
+	// unconditionally and rearrange the data as needed.
+	add		x9, ctx, #OFFSETOF_BUF
+	ld1		{v16.16b-v19.16b}, [x9]
+	st1		{v16.16b-v19.16b}, [sp]
+
+	ld1		{v16.16b-v19.16b}, [data1], #64
+	add		x9, sp, x8
+	st1		{v16.16b-v19.16b}, [x9]
+	ld1		{v16.4s-v19.4s}, [sp]
+
+	ld1		{v20.16b-v23.16b}, [data2], #64
+	st1		{v20.16b-v23.16b}, [x9]
+	ld1		{v20.4s-v23.4s}, [sp]
+
+	sub		len, len, #64
+	sub		data1, data1, x8
+	sub		data2, data2, x8
+	add		len, len, w8
+	mov		state0_b.16b, state0_a.16b
+	mov		state1_b.16b, state1_a.16b
+	b		.Lfinup2x_loop_have_data
+
+.Lfinup2x_enter_loop:
+	sub		len, len, #64
+	mov		state0_b.16b, state0_a.16b
+	mov		state1_b.16b, state1_a.16b
+.Lfinup2x_loop:
+	// Load the next two data blocks.
+	ld1		{v16.4s-v19.4s}, [data1], #64
+	ld1		{v20.4s-v23.4s}, [data2], #64
+.Lfinup2x_loop_have_data:
+	// Convert the words of the data blocks from big endian.
+CPU_LE(	rev32		v16.16b, v16.16b	)
+CPU_LE(	rev32		v17.16b, v17.16b	)
+CPU_LE(	rev32		v18.16b, v18.16b	)
+CPU_LE(	rev32		v19.16b, v19.16b	)
+CPU_LE(	rev32		v20.16b, v20.16b	)
+CPU_LE(	rev32		v21.16b, v21.16b	)
+CPU_LE(	rev32		v22.16b, v22.16b	)
+CPU_LE(	rev32		v23.16b, v23.16b	)
+.Lfinup2x_loop_have_bswapped_data:
+
+	// Save the original state for each block.
+	st1		{state0_a.4s-state1_b.4s}, [sp]
+
+	// Do the SHA-256 rounds on each block.
+	do_16rounds_2x	0,  v0, v1, v2, v3
+	do_16rounds_2x	16, v4, v5, v6, v7
+	do_16rounds_2x	32, v8, v9, v10, v11
+	do_16rounds_2x	48, v12, v13, v14, v15
+
+	// Add the original state for each block.
+	ld1		{v16.4s-v19.4s}, [sp]
+	add		state0_a.4s, state0_a.4s, v16.4s
+	add		state1_a.4s, state1_a.4s, v17.4s
+	add		state0_b.4s, state0_b.4s, v18.4s
+	add		state1_b.4s, state1_b.4s, v19.4s
+
+	// Update len and loop back if more blocks remain.
+	sub		len, len, #64
+	tbz		len, #31, .Lfinup2x_loop	// len >= 0?
+
+	// Check if any final blocks need to be handled.
+	// final_step = 2: all done
+	// final_step = 1: need to do count-only padding block
+	// final_step = 0: need to do the block with 0x80 padding byte
+	tbnz		final_step, #1, .Lfinup2x_done
+	tbnz		final_step, #0, .Lfinup2x_finalize_countonly
+	add		len, len, #64
+	cbz		len, .Lfinup2x_finalize_blockaligned
+
+	// Not block-aligned; 1 <= len <= 63 data bytes remain.  Pad the block.
+	// To do this, write the padding starting with the 0x80 byte to
+	// &sp[64].  Then for each message, copy the last 64 data bytes to sp
+	// and load from &sp[64 - len] to get the needed padding block.  This
+	// code relies on the data buffers being >= 64 bytes in length.
+	sub		w8, len, #64		// w8 = len - 64
+	add		data1, data1, w8, sxtw	// data1 += len - 64
+	add		data2, data2, w8, sxtw	// data2 += len - 64
+CPU_LE(	mov		x9, #0x80		)
+CPU_LE(	fmov		d16, x9			)
+CPU_BE(	movi		v16.16b, #0		)
+CPU_BE(	mov		x9, #0x8000000000000000	)
+CPU_BE(	mov		v16.d[1], x9		)
+	movi		v17.16b, #0
+	stp		q16, q17, [sp, #64]
+	stp		q17, q17, [sp, #96]
+	sub		x9, sp, w8, sxtw	// x9 = &sp[64 - len]
+	cmp		len, #56
+	b.ge		1f		// will count spill into its own block?
+	lsl		count, count, #3
+CPU_LE(	rev		count, count		)
+	str		count, [x9, #56]
+	mov		final_step, #2	// won't need count-only block
+	b		2f
+1:
+	mov		final_step, #1	// will need count-only block
+2:
+	ld1		{v16.16b-v19.16b}, [data1]
+	st1		{v16.16b-v19.16b}, [sp]
+	ld1		{v16.4s-v19.4s}, [x9]
+	ld1		{v20.16b-v23.16b}, [data2]
+	st1		{v20.16b-v23.16b}, [sp]
+	ld1		{v20.4s-v23.4s}, [x9]
+	b		.Lfinup2x_loop_have_data
+
+	// Prepare a padding block, either:
+	//
+	//	{0x80, 0, 0, 0, ..., count (as __be64)}
+	//	This is for a block aligned message.
+	//
+	//	{   0, 0, 0, 0, ..., count (as __be64)}
+	//	This is for a message whose length mod 64 is >= 56.
+	//
+	// Pre-swap the endianness of the words.
+.Lfinup2x_finalize_countonly:
+	movi		v16.2d, #0
+	b		1f
+.Lfinup2x_finalize_blockaligned:
+	mov		x8, #0x80000000
+	fmov		d16, x8
+1:
+	movi		v17.2d, #0
+	movi		v18.2d, #0
+	ror		count, count, #29	// ror(lsl(count, 3), 32)
+	mov		v19.d[0], xzr
+	mov		v19.d[1], count
+	mov		v20.16b, v16.16b
+	movi		v21.2d, #0
+	movi		v22.2d, #0
+	mov		v23.16b, v19.16b
+	mov		final_step, #2
+	b		.Lfinup2x_loop_have_bswapped_data
+
+.Lfinup2x_done:
+	// Write the two digests with all bytes in the correct order.
+CPU_LE(	rev32		state0_a.16b, state0_a.16b	)
+CPU_LE(	rev32		state1_a.16b, state1_a.16b	)
+CPU_LE(	rev32		state0_b.16b, state0_b.16b	)
+CPU_LE(	rev32		state1_b.16b, state1_b.16b	)
+	st1		{state0_a.4s-state1_a.4s}, [out1]
+	st1		{state0_b.4s-state1_b.4s}, [out2]
+	add		sp, sp, #128
+	ret
+SYM_FUNC_END(sha256_ce_finup2x)

lib/crypto/arm64/sha256.h

@@ -44,6 +44,43 @@ static void sha256_blocks(struct sha256_block_state *state,
 	}
 }
 
+static_assert(offsetof(struct __sha256_ctx, state) == 0);
+static_assert(offsetof(struct __sha256_ctx, bytecount) == 32);
+static_assert(offsetof(struct __sha256_ctx, buf) == 40);
+asmlinkage void sha256_ce_finup2x(const struct __sha256_ctx *ctx,
+				  const u8 *data1, const u8 *data2, int len,
+				  u8 out1[SHA256_DIGEST_SIZE],
+				  u8 out2[SHA256_DIGEST_SIZE]);
+
+#define sha256_finup_2x_arch sha256_finup_2x_arch
+static bool sha256_finup_2x_arch(const struct __sha256_ctx *ctx,
+				 const u8 *data1, const u8 *data2, size_t len,
+				 u8 out1[SHA256_DIGEST_SIZE],
+				 u8 out2[SHA256_DIGEST_SIZE])
+{
+	/*
+	 * The assembly requires len >= SHA256_BLOCK_SIZE && len <= INT_MAX.
+	 * Further limit len to 65536 to avoid spending too long with preemption
+	 * disabled.  (Of course, in practice len is nearly always 4096 anyway.)
+	 */
+	if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) &&
+	    static_branch_likely(&have_ce) && len >= SHA256_BLOCK_SIZE &&
+	    len <= 65536 && likely(may_use_simd())) {
+		kernel_neon_begin();
+		sha256_ce_finup2x(ctx, data1, data2, len, out1, out2);
+		kernel_neon_end();
+		kmsan_unpoison_memory(out1, SHA256_DIGEST_SIZE);
+		kmsan_unpoison_memory(out2, SHA256_DIGEST_SIZE);
+		return true;
+	}
+	return false;
+}
+
+static bool sha256_finup_2x_is_optimized_arch(void)
+{
+	return static_key_enabled(&have_ce);
+}
+
 #ifdef CONFIG_KERNEL_MODE_NEON
 #define sha256_mod_init_arch sha256_mod_init_arch
 static inline void sha256_mod_init_arch(void)