From c0eb7591c1ed9cbdb0ad796bb56aed13748b55fa Mon Sep 17 00:00:00 2001 From: Nathan Huckleberry Date: Fri, 20 May 2022 18:14:58 +0000 Subject: crypto: arm64/aes-xctr - Improve readability of XCTR and CTR modes Added some clarifying comments, changed the register allocations to make the code clearer, and added register aliases. Signed-off-by: Nathan Huckleberry Reviewed-by: Eric Biggers Signed-off-by: Herbert Xu --- arch/arm64/crypto/aes-glue.c | 16 +++ arch/arm64/crypto/aes-modes.S | 237 ++++++++++++++++++++++++++++++------------ 2 files changed, 185 insertions(+), 68 deletions(-) (limited to 'arch/arm64/crypto') diff --git a/arch/arm64/crypto/aes-glue.c b/arch/arm64/crypto/aes-glue.c index b6883288234c..162787c7aa86 100644 --- a/arch/arm64/crypto/aes-glue.c +++ b/arch/arm64/crypto/aes-glue.c @@ -464,6 +464,14 @@ static int __maybe_unused xctr_encrypt(struct skcipher_request *req) u8 *dst = walk.dst.virt.addr; u8 buf[AES_BLOCK_SIZE]; + /* + * If given less than 16 bytes, we must copy the partial block + * into a temporary buffer of 16 bytes to avoid out of bounds + * reads and writes. Furthermore, this code is somewhat unusual + * in that it expects the end of the data to be at the end of + * the temporary buffer, rather than the start of the data at + * the start of the temporary buffer. + */ if (unlikely(nbytes < AES_BLOCK_SIZE)) src = dst = memcpy(buf + sizeof(buf) - nbytes, src, nbytes); @@ -501,6 +509,14 @@ static int __maybe_unused ctr_encrypt(struct skcipher_request *req) u8 *dst = walk.dst.virt.addr; u8 buf[AES_BLOCK_SIZE]; + /* + * If given less than 16 bytes, we must copy the partial block + * into a temporary buffer of 16 bytes to avoid out of bounds + * reads and writes. Furthermore, this code is somewhat unusual + * in that it expects the end of the data to be at the end of + * the temporary buffer, rather than the start of the data at + * the start of the temporary buffer. + */ if (unlikely(nbytes < AES_BLOCK_SIZE)) src = dst = memcpy(buf + sizeof(buf) - nbytes, src, nbytes); diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S index 6c36a3b0ed7d..5abc834271f4 100644 --- a/arch/arm64/crypto/aes-modes.S +++ b/arch/arm64/crypto/aes-modes.S @@ -322,32 +322,60 @@ AES_FUNC_END(aes_cbc_cts_decrypt) * This macro generates the code for CTR and XCTR mode. */ .macro ctr_encrypt xctr + // Arguments + OUT .req x0 + IN .req x1 + KEY .req x2 + ROUNDS_W .req w3 + BYTES_W .req w4 + IV .req x5 + BYTE_CTR_W .req w6 // XCTR only + // Intermediate values + CTR_W .req w11 // XCTR only + CTR .req x11 // XCTR only + IV_PART .req x12 + BLOCKS .req x13 + BLOCKS_W .req w13 + stp x29, x30, [sp, #-16]! mov x29, sp - enc_prepare w3, x2, x12 - ld1 {vctr.16b}, [x5] + enc_prepare ROUNDS_W, KEY, IV_PART + ld1 {vctr.16b}, [IV] + /* + * Keep 64 bits of the IV in a register. For CTR mode this lets us + * easily increment the IV. For XCTR mode this lets us efficiently XOR + * the 64-bit counter with the IV. + */ .if \xctr - umov x12, vctr.d[0] - lsr w11, w6, #4 + umov IV_PART, vctr.d[0] + lsr CTR_W, BYTE_CTR_W, #4 .else - umov x12, vctr.d[1] /* keep swabbed ctr in reg */ - rev x12, x12 + umov IV_PART, vctr.d[1] + rev IV_PART, IV_PART .endif .LctrloopNx\xctr: - add w7, w4, #15 - sub w4, w4, #MAX_STRIDE << 4 - lsr w7, w7, #4 + add BLOCKS_W, BYTES_W, #15 + sub BYTES_W, BYTES_W, #MAX_STRIDE << 4 + lsr BLOCKS_W, BLOCKS_W, #4 mov w8, #MAX_STRIDE - cmp w7, w8 - csel w7, w7, w8, lt + cmp BLOCKS_W, w8 + csel BLOCKS_W, BLOCKS_W, w8, lt + /* + * Set up the counter values in v0-v{MAX_STRIDE-1}. + * + * If we are encrypting less than MAX_STRIDE blocks, the tail block + * handling code expects the last keystream block to be in + * v{MAX_STRIDE-1}. For example: if encrypting two blocks with + * MAX_STRIDE=5, then v3 and v4 should have the next two counter blocks. + */ .if \xctr - add x11, x11, x7 + add CTR, CTR, BLOCKS .else - adds x12, x12, x7 + adds IV_PART, IV_PART, BLOCKS .endif mov v0.16b, vctr.16b mov v1.16b, vctr.16b @@ -355,16 +383,16 @@ AES_FUNC_END(aes_cbc_cts_decrypt) mov v3.16b, vctr.16b ST5( mov v4.16b, vctr.16b ) .if \xctr - sub x6, x11, #MAX_STRIDE - 1 - sub x7, x11, #MAX_STRIDE - 2 - sub x8, x11, #MAX_STRIDE - 3 - sub x9, x11, #MAX_STRIDE - 4 -ST5( sub x10, x11, #MAX_STRIDE - 5 ) - eor x6, x6, x12 - eor x7, x7, x12 - eor x8, x8, x12 - eor x9, x9, x12 -ST5( eor x10, x10, x12 ) + sub x6, CTR, #MAX_STRIDE - 1 + sub x7, CTR, #MAX_STRIDE - 2 + sub x8, CTR, #MAX_STRIDE - 3 + sub x9, CTR, #MAX_STRIDE - 4 +ST5( sub x10, CTR, #MAX_STRIDE - 5 ) + eor x6, x6, IV_PART + eor x7, x7, IV_PART + eor x8, x8, IV_PART + eor x9, x9, IV_PART +ST5( eor x10, x10, IV_PART ) mov v0.d[0], x6 mov v1.d[0], x7 mov v2.d[0], x8 @@ -373,17 +401,32 @@ ST5( mov v4.d[0], x10 ) .else bcs 0f .subsection 1 - /* apply carry to outgoing counter */ + /* + * This subsection handles carries. + * + * Conditional branching here is allowed with respect to time + * invariance since the branches are dependent on the IV instead + * of the plaintext or key. This code is rarely executed in + * practice anyway. + */ + + /* Apply carry to outgoing counter. */ 0: umov x8, vctr.d[0] rev x8, x8 add x8, x8, #1 rev x8, x8 ins vctr.d[0], x8 - /* apply carry to N counter blocks for N := x12 */ - cbz x12, 2f + /* + * Apply carry to counter blocks if needed. + * + * Since the carry flag was set, we know 0 <= IV_PART < + * MAX_STRIDE. Using the value of IV_PART we can determine how + * many counter blocks need to be updated. + */ + cbz IV_PART, 2f adr x16, 1f - sub x16, x16, x12, lsl #3 + sub x16, x16, IV_PART, lsl #3 br x16 bti c mov v0.d[0], vctr.d[0] @@ -398,71 +441,88 @@ ST5( mov v4.d[0], vctr.d[0] ) 1: b 2f .previous -2: rev x7, x12 +2: rev x7, IV_PART ins vctr.d[1], x7 - sub x7, x12, #MAX_STRIDE - 1 - sub x8, x12, #MAX_STRIDE - 2 - sub x9, x12, #MAX_STRIDE - 3 + sub x7, IV_PART, #MAX_STRIDE - 1 + sub x8, IV_PART, #MAX_STRIDE - 2 + sub x9, IV_PART, #MAX_STRIDE - 3 rev x7, x7 rev x8, x8 mov v1.d[1], x7 rev x9, x9 -ST5( sub x10, x12, #MAX_STRIDE - 4 ) +ST5( sub x10, IV_PART, #MAX_STRIDE - 4 ) mov v2.d[1], x8 ST5( rev x10, x10 ) mov v3.d[1], x9 ST5( mov v4.d[1], x10 ) .endif - tbnz w4, #31, .Lctrtail\xctr - ld1 {v5.16b-v7.16b}, [x1], #48 + + /* + * If there are at least MAX_STRIDE blocks left, XOR the data with + * keystream and store. Otherwise jump to tail handling. + */ + tbnz BYTES_W, #31, .Lctrtail\xctr + ld1 {v5.16b-v7.16b}, [IN], #48 ST4( bl aes_encrypt_block4x ) ST5( bl aes_encrypt_block5x ) eor v0.16b, v5.16b, v0.16b -ST4( ld1 {v5.16b}, [x1], #16 ) +ST4( ld1 {v5.16b}, [IN], #16 ) eor v1.16b, v6.16b, v1.16b -ST5( ld1 {v5.16b-v6.16b}, [x1], #32 ) +ST5( ld1 {v5.16b-v6.16b}, [IN], #32 ) eor v2.16b, v7.16b, v2.16b eor v3.16b, v5.16b, v3.16b ST5( eor v4.16b, v6.16b, v4.16b ) - st1 {v0.16b-v3.16b}, [x0], #64 -ST5( st1 {v4.16b}, [x0], #16 ) - cbz w4, .Lctrout\xctr + st1 {v0.16b-v3.16b}, [OUT], #64 +ST5( st1 {v4.16b}, [OUT], #16 ) + cbz BYTES_W, .Lctrout\xctr b .LctrloopNx\xctr .Lctrout\xctr: .if !\xctr - st1 {vctr.16b}, [x5] /* return next CTR value */ + st1 {vctr.16b}, [IV] /* return next CTR value */ .endif ldp x29, x30, [sp], #16 ret .Lctrtail\xctr: + /* + * Handle up to MAX_STRIDE * 16 - 1 bytes of plaintext + * + * This code expects the last keystream block to be in v{MAX_STRIDE-1}. + * For example: if encrypting two blocks with MAX_STRIDE=5, then v3 and + * v4 should have the next two counter blocks. + * + * This allows us to store the ciphertext by writing to overlapping + * regions of memory. Any invalid ciphertext blocks get overwritten by + * correctly computed blocks. This approach greatly simplifies the + * logic for storing the ciphertext. + */ mov x16, #16 - ands x6, x4, #0xf - csel x13, x6, x16, ne + ands w7, BYTES_W, #0xf + csel x13, x7, x16, ne -ST5( cmp w4, #64 - (MAX_STRIDE << 4) ) +ST5( cmp BYTES_W, #64 - (MAX_STRIDE << 4)) ST5( csel x14, x16, xzr, gt ) - cmp w4, #48 - (MAX_STRIDE << 4) + cmp BYTES_W, #48 - (MAX_STRIDE << 4) csel x15, x16, xzr, gt - cmp w4, #32 - (MAX_STRIDE << 4) + cmp BYTES_W, #32 - (MAX_STRIDE << 4) csel x16, x16, xzr, gt - cmp w4, #16 - (MAX_STRIDE << 4) + cmp BYTES_W, #16 - (MAX_STRIDE << 4) - adr_l x12, .Lcts_permute_table - add x12, x12, x13 + adr_l x9, .Lcts_permute_table + add x9, x9, x13 ble .Lctrtail1x\xctr -ST5( ld1 {v5.16b}, [x1], x14 ) - ld1 {v6.16b}, [x1], x15 - ld1 {v7.16b}, [x1], x16 +ST5( ld1 {v5.16b}, [IN], x14 ) + ld1 {v6.16b}, [IN], x15 + ld1 {v7.16b}, [IN], x16 ST4( bl aes_encrypt_block4x ) ST5( bl aes_encrypt_block5x ) - ld1 {v8.16b}, [x1], x13 - ld1 {v9.16b}, [x1] - ld1 {v10.16b}, [x12] + ld1 {v8.16b}, [IN], x13 + ld1 {v9.16b}, [IN] + ld1 {v10.16b}, [x9] ST4( eor v6.16b, v6.16b, v0.16b ) ST4( eor v7.16b, v7.16b, v1.16b ) @@ -477,35 +537,70 @@ ST5( eor v7.16b, v7.16b, v2.16b ) ST5( eor v8.16b, v8.16b, v3.16b ) ST5( eor v9.16b, v9.16b, v4.16b ) -ST5( st1 {v5.16b}, [x0], x14 ) - st1 {v6.16b}, [x0], x15 - st1 {v7.16b}, [x0], x16 - add x13, x13, x0 +ST5( st1 {v5.16b}, [OUT], x14 ) + st1 {v6.16b}, [OUT], x15 + st1 {v7.16b}, [OUT], x16 + add x13, x13, OUT st1 {v9.16b}, [x13] // overlapping stores - st1 {v8.16b}, [x0] + st1 {v8.16b}, [OUT] b .Lctrout\xctr .Lctrtail1x\xctr: - sub x7, x6, #16 - csel x6, x6, x7, eq - add x1, x1, x6 - add x0, x0, x6 - ld1 {v5.16b}, [x1] - ld1 {v6.16b}, [x0] + /* + * Handle <= 16 bytes of plaintext + * + * This code always reads and writes 16 bytes. To avoid out of bounds + * accesses, XCTR and CTR modes must use a temporary buffer when + * encrypting/decrypting less than 16 bytes. + * + * This code is unusual in that it loads the input and stores the output + * relative to the end of the buffers rather than relative to the start. + * This causes unusual behaviour when encrypting/decrypting less than 16 + * bytes; the end of the data is expected to be at the end of the + * temporary buffer rather than the start of the data being at the start + * of the temporary buffer. + */ + sub x8, x7, #16 + csel x7, x7, x8, eq + add IN, IN, x7 + add OUT, OUT, x7 + ld1 {v5.16b}, [IN] + ld1 {v6.16b}, [OUT] ST5( mov v3.16b, v4.16b ) - encrypt_block v3, w3, x2, x8, w7 - ld1 {v10.16b-v11.16b}, [x12] + encrypt_block v3, ROUNDS_W, KEY, x8, w7 + ld1 {v10.16b-v11.16b}, [x9] tbl v3.16b, {v3.16b}, v10.16b sshr v11.16b, v11.16b, #7 eor v5.16b, v5.16b, v3.16b bif v5.16b, v6.16b, v11.16b - st1 {v5.16b}, [x0] + st1 {v5.16b}, [OUT] b .Lctrout\xctr + + // Arguments + .unreq OUT + .unreq IN + .unreq KEY + .unreq ROUNDS_W + .unreq BYTES_W + .unreq IV + .unreq BYTE_CTR_W // XCTR only + // Intermediate values + .unreq CTR_W // XCTR only + .unreq CTR // XCTR only + .unreq IV_PART + .unreq BLOCKS + .unreq BLOCKS_W .endm /* * aes_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[], int rounds, * int bytes, u8 ctr[]) + * + * The input and output buffers must always be at least 16 bytes even if + * encrypting/decrypting less than 16 bytes. Otherwise out of bounds + * accesses will occur. The data to be encrypted/decrypted is expected + * to be at the end of this 16-byte temporary buffer rather than the + * start. */ AES_FUNC_START(aes_ctr_encrypt) @@ -515,6 +610,12 @@ AES_FUNC_END(aes_ctr_encrypt) /* * aes_xctr_encrypt(u8 out[], u8 const in[], u8 const rk[], int rounds, * int bytes, u8 const iv[], int byte_ctr) + * + * The input and output buffers must always be at least 16 bytes even if + * encrypting/decrypting less than 16 bytes. Otherwise out of bounds + * accesses will occur. The data to be encrypted/decrypted is expected + * to be at the end of this 16-byte temporary buffer rather than the + * start. */ AES_FUNC_START(aes_xctr_encrypt) -- cgit