--- /dev/null
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2018 Google, Inc.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+ * Design notes:
+ *
+ * 16 registers would be needed to hold the state matrix, but only 14 are
+ * available because 'sp' and 'pc' cannot be used. So we spill the elements
+ * (x8, x9) to the stack and swap them out with (x10, x11). This adds one
+ * 'ldrd' and one 'strd' instruction per round.
+ *
+ * All rotates are performed using the implicit rotate operand accepted by the
+ * 'add' and 'eor' instructions. This is faster than using explicit rotate
+ * instructions. To make this work, we allow the values in the second and last
+ * rows of the ChaCha state matrix (rows 'b' and 'd') to temporarily have the
+ * wrong rotation amount. The rotation amount is then fixed up just in time
+ * when the values are used. 'brot' is the number of bits the values in row 'b'
+ * need to be rotated right to arrive at the correct values, and 'drot'
+ * similarly for row 'd'. (brot, drot) start out as (0, 0) but we make it such
+ * that they end up as (25, 24) after every round.
+ */
+
+ // ChaCha state registers
+ X0 .req r0
+ X1 .req r1
+ X2 .req r2
+ X3 .req r3
+ X4 .req r4
+ X5 .req r5
+ X6 .req r6
+ X7 .req r7
+ X8_X10 .req r8 // shared by x8 and x10
+ X9_X11 .req r9 // shared by x9 and x11
+ X12 .req r10
+ X13 .req r11
+ X14 .req r12
+ X15 .req r14
+
+.Lexpand_32byte_k:
+ // "expand 32-byte k"
+ .word 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574
+
+#ifdef __thumb2__
+# define adrl adr
+#endif
+
+.macro __rev out, in, t0, t1, t2
+.if __LINUX_ARM_ARCH__ >= 6
+ rev \out, \in
+.else
+ lsl \t0, \in, #24
+ and \t1, \in, #0xff00
+ and \t2, \in, #0xff0000
+ orr \out, \t0, \in, lsr #24
+ orr \out, \out, \t1, lsl #8
+ orr \out, \out, \t2, lsr #8
+.endif
+.endm
+
+.macro _le32_bswap x, t0, t1, t2
+#ifdef __ARMEB__
+ __rev \x, \x, \t0, \t1, \t2
+#endif
+.endm
+
+.macro _le32_bswap_4x a, b, c, d, t0, t1, t2
+ _le32_bswap \a, \t0, \t1, \t2
+ _le32_bswap \b, \t0, \t1, \t2
+ _le32_bswap \c, \t0, \t1, \t2
+ _le32_bswap \d, \t0, \t1, \t2
+.endm
+
+.macro __ldrd a, b, src, offset
+#if __LINUX_ARM_ARCH__ >= 6
+ ldrd \a, \b, [\src, #\offset]
+#else
+ ldr \a, [\src, #\offset]
+ ldr \b, [\src, #\offset + 4]
+#endif
+.endm
+
+.macro __strd a, b, dst, offset
+#if __LINUX_ARM_ARCH__ >= 6
+ strd \a, \b, [\dst, #\offset]
+#else
+ str \a, [\dst, #\offset]
+ str \b, [\dst, #\offset + 4]
+#endif
+.endm
+
+.macro _halfround a1, b1, c1, d1, a2, b2, c2, d2
+
+ // a += b; d ^= a; d = rol(d, 16);
+ add \a1, \a1, \b1, ror #brot
+ add \a2, \a2, \b2, ror #brot
+ eor \d1, \a1, \d1, ror #drot
+ eor \d2, \a2, \d2, ror #drot
+ // drot == 32 - 16 == 16
+
+ // c += d; b ^= c; b = rol(b, 12);
+ add \c1, \c1, \d1, ror #16
+ add \c2, \c2, \d2, ror #16
+ eor \b1, \c1, \b1, ror #brot
+ eor \b2, \c2, \b2, ror #brot
+ // brot == 32 - 12 == 20
+
+ // a += b; d ^= a; d = rol(d, 8);
+ add \a1, \a1, \b1, ror #20
+ add \a2, \a2, \b2, ror #20
+ eor \d1, \a1, \d1, ror #16
+ eor \d2, \a2, \d2, ror #16
+ // drot == 32 - 8 == 24
+
+ // c += d; b ^= c; b = rol(b, 7);
+ add \c1, \c1, \d1, ror #24
+ add \c2, \c2, \d2, ror #24
+ eor \b1, \c1, \b1, ror #20
+ eor \b2, \c2, \b2, ror #20
+ // brot == 32 - 7 == 25
+.endm
+
+.macro _doubleround
+
+ // column round
+
+ // quarterrounds: (x0, x4, x8, x12) and (x1, x5, x9, x13)
+ _halfround X0, X4, X8_X10, X12, X1, X5, X9_X11, X13
+
+ // save (x8, x9); restore (x10, x11)
+ __strd X8_X10, X9_X11, sp, 0
+ __ldrd X8_X10, X9_X11, sp, 8
+
+ // quarterrounds: (x2, x6, x10, x14) and (x3, x7, x11, x15)
+ _halfround X2, X6, X8_X10, X14, X3, X7, X9_X11, X15
+
+ .set brot, 25
+ .set drot, 24
+
+ // diagonal round
+
+ // quarterrounds: (x0, x5, x10, x15) and (x1, x6, x11, x12)
+ _halfround X0, X5, X8_X10, X15, X1, X6, X9_X11, X12
+
+ // save (x10, x11); restore (x8, x9)
+ __strd X8_X10, X9_X11, sp, 8
+ __ldrd X8_X10, X9_X11, sp, 0
+
+ // quarterrounds: (x2, x7, x8, x13) and (x3, x4, x9, x14)
+ _halfround X2, X7, X8_X10, X13, X3, X4, X9_X11, X14
+.endm
+
+.macro _chacha_permute nrounds
+ .set brot, 0
+ .set drot, 0
+ .rept \nrounds / 2
+ _doubleround
+ .endr
+.endm
+
+.macro _chacha nrounds
+
+.Lnext_block\@:
+ // Stack: unused0-unused1 x10-x11 x0-x15 OUT IN LEN
+ // Registers contain x0-x9,x12-x15.
+
+ // Do the core ChaCha permutation to update x0-x15.
+ _chacha_permute \nrounds
+
+ add sp, #8
+ // Stack: x10-x11 orig_x0-orig_x15 OUT IN LEN
+ // Registers contain x0-x9,x12-x15.
+ // x4-x7 are rotated by 'brot'; x12-x15 are rotated by 'drot'.
+
+ // Free up some registers (r8-r12,r14) by pushing (x8-x9,x12-x15).
+ push {X8_X10, X9_X11, X12, X13, X14, X15}
+
+ // Load (OUT, IN, LEN).
+ ldr r14, [sp, #96]
+ ldr r12, [sp, #100]
+ ldr r11, [sp, #104]
+
+ orr r10, r14, r12
+
+ // Use slow path if fewer than 64 bytes remain.
+ cmp r11, #64
+ blt .Lxor_slowpath\@
+
+ // Use slow path if IN and/or OUT isn't 4-byte aligned. Needed even on
+ // ARMv6+, since ldmia and stmia (used below) still require alignment.
+ tst r10, #3
+ bne .Lxor_slowpath\@
+
+ // Fast path: XOR 64 bytes of aligned data.
+
+ // Stack: x8-x9 x12-x15 x10-x11 orig_x0-orig_x15 OUT IN LEN
+ // Registers: r0-r7 are x0-x7; r8-r11 are free; r12 is IN; r14 is OUT.
+ // x4-x7 are rotated by 'brot'; x12-x15 are rotated by 'drot'.
+
+ // x0-x3
+ __ldrd r8, r9, sp, 32
+ __ldrd r10, r11, sp, 40
+ add X0, X0, r8
+ add X1, X1, r9
+ add X2, X2, r10
+ add X3, X3, r11
+ _le32_bswap_4x X0, X1, X2, X3, r8, r9, r10
+ ldmia r12!, {r8-r11}
+ eor X0, X0, r8
+ eor X1, X1, r9
+ eor X2, X2, r10
+ eor X3, X3, r11
+ stmia r14!, {X0-X3}
+
+ // x4-x7
+ __ldrd r8, r9, sp, 48
+ __ldrd r10, r11, sp, 56
+ add X4, r8, X4, ror #brot
+ add X5, r9, X5, ror #brot
+ ldmia r12!, {X0-X3}
+ add X6, r10, X6, ror #brot
+ add X7, r11, X7, ror #brot
+ _le32_bswap_4x X4, X5, X6, X7, r8, r9, r10
+ eor X4, X4, X0
+ eor X5, X5, X1
+ eor X6, X6, X2
+ eor X7, X7, X3
+ stmia r14!, {X4-X7}
+
+ // x8-x15
+ pop {r0-r7} // (x8-x9,x12-x15,x10-x11)
+ __ldrd r8, r9, sp, 32
+ __ldrd r10, r11, sp, 40
+ add r0, r0, r8 // x8
+ add r1, r1, r9 // x9
+ add r6, r6, r10 // x10
+ add r7, r7, r11 // x11
+ _le32_bswap_4x r0, r1, r6, r7, r8, r9, r10
+ ldmia r12!, {r8-r11}
+ eor r0, r0, r8 // x8
+ eor r1, r1, r9 // x9
+ eor r6, r6, r10 // x10
+ eor r7, r7, r11 // x11
+ stmia r14!, {r0,r1,r6,r7}
+ ldmia r12!, {r0,r1,r6,r7}
+ __ldrd r8, r9, sp, 48
+ __ldrd r10, r11, sp, 56
+ add r2, r8, r2, ror #drot // x12
+ add r3, r9, r3, ror #drot // x13
+ add r4, r10, r4, ror #drot // x14
+ add r5, r11, r5, ror #drot // x15
+ _le32_bswap_4x r2, r3, r4, r5, r9, r10, r11
+ ldr r9, [sp, #72] // load LEN
+ eor r2, r2, r0 // x12
+ eor r3, r3, r1 // x13
+ eor r4, r4, r6 // x14
+ eor r5, r5, r7 // x15
+ subs r9, #64 // decrement and check LEN
+ stmia r14!, {r2-r5}
+
+ beq .Ldone\@
+
+.Lprepare_for_next_block\@:
+
+ // Stack: x0-x15 OUT IN LEN
+
+ // Increment block counter (x12)
+ add r8, #1
+
+ // Store updated (OUT, IN, LEN)
+ str r14, [sp, #64]
+ str r12, [sp, #68]
+ str r9, [sp, #72]
+
+ mov r14, sp
+
+ // Store updated block counter (x12)
+ str r8, [sp, #48]
+
+ sub sp, #16
+
+ // Reload state and do next block
+ ldmia r14!, {r0-r11} // load x0-x11
+ __strd r10, r11, sp, 8 // store x10-x11 before state
+ ldmia r14, {r10-r12,r14} // load x12-x15
+ b .Lnext_block\@
+
+.Lxor_slowpath\@:
+ // Slow path: < 64 bytes remaining, or unaligned input or output buffer.
+ // We handle it by storing the 64 bytes of keystream to the stack, then
+ // XOR-ing the needed portion with the data.
+
+ // Allocate keystream buffer
+ sub sp, #64
+ mov r14, sp
+
+ // Stack: ks0-ks15 x8-x9 x12-x15 x10-x11 orig_x0-orig_x15 OUT IN LEN
+ // Registers: r0-r7 are x0-x7; r8-r11 are free; r12 is IN; r14 is &ks0.
+ // x4-x7 are rotated by 'brot'; x12-x15 are rotated by 'drot'.
+
+ // Save keystream for x0-x3
+ __ldrd r8, r9, sp, 96
+ __ldrd r10, r11, sp, 104
+ add X0, X0, r8
+ add X1, X1, r9
+ add X2, X2, r10
+ add X3, X3, r11
+ _le32_bswap_4x X0, X1, X2, X3, r8, r9, r10
+ stmia r14!, {X0-X3}
+
+ // Save keystream for x4-x7
+ __ldrd r8, r9, sp, 112
+ __ldrd r10, r11, sp, 120
+ add X4, r8, X4, ror #brot
+ add X5, r9, X5, ror #brot
+ add X6, r10, X6, ror #brot
+ add X7, r11, X7, ror #brot
+ _le32_bswap_4x X4, X5, X6, X7, r8, r9, r10
+ add r8, sp, #64
+ stmia r14!, {X4-X7}
+
+ // Save keystream for x8-x15
+ ldm r8, {r0-r7} // (x8-x9,x12-x15,x10-x11)
+ __ldrd r8, r9, sp, 128
+ __ldrd r10, r11, sp, 136
+ add r0, r0, r8 // x8
+ add r1, r1, r9 // x9
+ add r6, r6, r10 // x10
+ add r7, r7, r11 // x11
+ _le32_bswap_4x r0, r1, r6, r7, r8, r9, r10
+ stmia r14!, {r0,r1,r6,r7}
+ __ldrd r8, r9, sp, 144
+ __ldrd r10, r11, sp, 152
+ add r2, r8, r2, ror #drot // x12
+ add r3, r9, r3, ror #drot // x13
+ add r4, r10, r4, ror #drot // x14
+ add r5, r11, r5, ror #drot // x15
+ _le32_bswap_4x r2, r3, r4, r5, r9, r10, r11
+ stmia r14, {r2-r5}
+
+ // Stack: ks0-ks15 unused0-unused7 x0-x15 OUT IN LEN
+ // Registers: r8 is block counter, r12 is IN.
+
+ ldr r9, [sp, #168] // LEN
+ ldr r14, [sp, #160] // OUT
+ cmp r9, #64
+ mov r0, sp
+ movle r1, r9
+ movgt r1, #64
+ // r1 is number of bytes to XOR, in range [1, 64]
+
+.if __LINUX_ARM_ARCH__ < 6
+ orr r2, r12, r14
+ tst r2, #3 // IN or OUT misaligned?
+ bne .Lxor_next_byte\@
+.endif
+
+ // XOR a word at a time
+.rept 16
+ subs r1, #4
+ blt .Lxor_words_done\@
+ ldr r2, [r12], #4
+ ldr r3, [r0], #4
+ eor r2, r2, r3
+ str r2, [r14], #4
+.endr
+ b .Lxor_slowpath_done\@
+.Lxor_words_done\@:
+ ands r1, r1, #3
+ beq .Lxor_slowpath_done\@
+
+ // XOR a byte at a time
+.Lxor_next_byte\@:
+ ldrb r2, [r12], #1
+ ldrb r3, [r0], #1
+ eor r2, r2, r3
+ strb r2, [r14], #1
+ subs r1, #1
+ bne .Lxor_next_byte\@
+
+.Lxor_slowpath_done\@:
+ subs r9, #64
+ add sp, #96
+ bgt .Lprepare_for_next_block\@
+
+.Ldone\@:
+.endm // _chacha
+
+/*
+ * void chacha20_arm(u8 *out, const u8 *in, size_t len, const u32 key[8],
+ * const u32 iv[4]);
+ */
+ENTRY(chacha20_arm)
+ cmp r2, #0 // len == 0?
+ reteq lr
+
+ push {r0-r2,r4-r11,lr}
+
+ // Push state x0-x15 onto stack.
+ // Also store an extra copy of x10-x11 just before the state.
+
+ ldr r4, [sp, #48] // iv
+ mov r0, sp
+ sub sp, #80
+
+ // iv: x12-x15
+ ldm r4, {X12,X13,X14,X15}
+ stmdb r0!, {X12,X13,X14,X15}
+
+ // key: x4-x11
+ __ldrd X8_X10, X9_X11, r3, 24
+ __strd X8_X10, X9_X11, sp, 8
+ stmdb r0!, {X8_X10, X9_X11}
+ ldm r3, {X4-X9_X11}
+ stmdb r0!, {X4-X9_X11}
+
+ // constants: x0-x3
+ adrl X3, .Lexpand_32byte_k
+ ldm X3, {X0-X3}
+ __strd X0, X1, sp, 16
+ __strd X2, X3, sp, 24
+
+ _chacha 20
+
+ add sp, #76
+ pop {r4-r11, pc}
+ENDPROC(chacha20_arm)
+
+/*
+ * void hchacha20_arm(const u32 state[16], u32 out[8]);
+ */
+ENTRY(hchacha20_arm)
+ push {r1,r4-r11,lr}
+
+ mov r14, r0
+ ldmia r14!, {r0-r11} // load x0-x11
+ push {r10-r11} // store x10-x11 to stack
+ ldm r14, {r10-r12,r14} // load x12-x15
+ sub sp, #8
+
+ _chacha_permute 20
+
+ // Skip over (unused0-unused1, x10-x11)
+ add sp, #16
+
+ // Fix up rotations of x12-x15
+ ror X12, X12, #drot
+ ror X13, X13, #drot
+ pop {r4} // load 'out'
+ ror X14, X14, #drot
+ ror X15, X15, #drot
+
+ // Store (x0-x3,x12-x15) to 'out'
+ stm r4, {X0,X1,X2,X3,X12,X13,X14,X15}
+
+ pop {r4-r11,pc}
+ENDPROC(hchacha20_arm)
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