diff options
Diffstat (limited to 'arch/arm')
| -rw-r--r-- | arch/arm/crypto/Kconfig | 9 | ||||
| -rw-r--r-- | arch/arm/crypto/aes-cipher-core.S | 62 |
2 files changed, 61 insertions, 10 deletions
diff --git a/arch/arm/crypto/Kconfig b/arch/arm/crypto/Kconfig index ef0c7feea6e2..0473a8f68389 100644 --- a/arch/arm/crypto/Kconfig +++ b/arch/arm/crypto/Kconfig @@ -69,6 +69,15 @@ config CRYPTO_AES_ARM help Use optimized AES assembler routines for ARM platforms. + On ARM processors without the Crypto Extensions, this is the + fastest AES implementation for single blocks. For multiple + blocks, the NEON bit-sliced implementation is usually faster. + + This implementation may be vulnerable to cache timing attacks, + since it uses lookup tables. However, as countermeasures it + disables IRQs and preloads the tables; it is hoped this makes + such attacks very difficult. + config CRYPTO_AES_ARM_BS tristate "Bit sliced AES using NEON instructions" depends on KERNEL_MODE_NEON diff --git a/arch/arm/crypto/aes-cipher-core.S b/arch/arm/crypto/aes-cipher-core.S index 184d6c2d15d5..f2d67c095e59 100644 --- a/arch/arm/crypto/aes-cipher-core.S +++ b/arch/arm/crypto/aes-cipher-core.S @@ -10,6 +10,7 @@ */ #include <linux/linkage.h> +#include <asm/assembler.h> #include <asm/cache.h> .text @@ -41,7 +42,7 @@ .endif .endm - .macro __hround, out0, out1, in0, in1, in2, in3, t3, t4, enc, sz, op + .macro __hround, out0, out1, in0, in1, in2, in3, t3, t4, enc, sz, op, oldcpsr __select \out0, \in0, 0 __select t0, \in1, 1 __load \out0, \out0, 0, \sz, \op @@ -73,6 +74,14 @@ __load t0, t0, 3, \sz, \op __load \t4, \t4, 3, \sz, \op + .ifnb \oldcpsr + /* + * This is the final round and we're done with all data-dependent table + * lookups, so we can safely re-enable interrupts. + */ + restore_irqs \oldcpsr + .endif + eor \out1, \out1, t1, ror #24 eor \out0, \out0, t2, ror #16 ldm rk!, {t1, t2} @@ -83,14 +92,14 @@ eor \out1, \out1, t2 .endm - .macro fround, out0, out1, out2, out3, in0, in1, in2, in3, sz=2, op + .macro fround, out0, out1, out2, out3, in0, in1, in2, in3, sz=2, op, oldcpsr __hround \out0, \out1, \in0, \in1, \in2, \in3, \out2, \out3, 1, \sz, \op - __hround \out2, \out3, \in2, \in3, \in0, \in1, \in1, \in2, 1, \sz, \op + __hround \out2, \out3, \in2, \in3, \in0, \in1, \in1, \in2, 1, \sz, \op, \oldcpsr .endm - .macro iround, out0, out1, out2, out3, in0, in1, in2, in3, sz=2, op + .macro iround, out0, out1, out2, out3, in0, in1, in2, in3, sz=2, op, oldcpsr __hround \out0, \out1, \in0, \in3, \in2, \in1, \out2, \out3, 0, \sz, \op - __hround \out2, \out3, \in2, \in1, \in0, \in3, \in1, \in0, 0, \sz, \op + __hround \out2, \out3, \in2, \in1, \in0, \in3, \in1, \in0, 0, \sz, \op, \oldcpsr .endm .macro __rev, out, in @@ -118,13 +127,14 @@ .macro do_crypt, round, ttab, ltab, bsz push {r3-r11, lr} + // Load keys first, to reduce latency in case they're not cached yet. + ldm rk!, {r8-r11} + ldr r4, [in] ldr r5, [in, #4] ldr r6, [in, #8] ldr r7, [in, #12] - ldm rk!, {r8-r11} - #ifdef CONFIG_CPU_BIG_ENDIAN __rev r4, r4 __rev r5, r5 @@ -138,6 +148,25 @@ eor r7, r7, r11 __adrl ttab, \ttab + /* + * Disable interrupts and prefetch the 1024-byte 'ft' or 'it' table into + * L1 cache, assuming cacheline size >= 32. This is a hardening measure + * intended to make cache-timing attacks more difficult. They may not + * be fully prevented, however; see the paper + * https://cr.yp.to/antiforgery/cachetiming-20050414.pdf + * ("Cache-timing attacks on AES") for a discussion of the many + * difficulties involved in writing truly constant-time AES software. + */ + save_and_disable_irqs t0 + .set i, 0 + .rept 1024 / 128 + ldr r8, [ttab, #i + 0] + ldr r9, [ttab, #i + 32] + ldr r10, [ttab, #i + 64] + ldr r11, [ttab, #i + 96] + .set i, i + 128 + .endr + push {t0} // oldcpsr tst rounds, #2 bne 1f @@ -151,8 +180,21 @@ \round r4, r5, r6, r7, r8, r9, r10, r11 b 0b -2: __adrl ttab, \ltab - \round r4, r5, r6, r7, r8, r9, r10, r11, \bsz, b +2: .ifb \ltab + add ttab, ttab, #1 + .else + __adrl ttab, \ltab + // Prefetch inverse S-box for final round; see explanation above + .set i, 0 + .rept 256 / 64 + ldr t0, [ttab, #i + 0] + ldr t1, [ttab, #i + 32] + .set i, i + 64 + .endr + .endif + + pop {rounds} // oldcpsr + \round r4, r5, r6, r7, r8, r9, r10, r11, \bsz, b, rounds #ifdef CONFIG_CPU_BIG_ENDIAN __rev r4, r4 @@ -175,7 +217,7 @@ .endm ENTRY(__aes_arm_encrypt) - do_crypt fround, crypto_ft_tab, crypto_ft_tab + 1, 2 + do_crypt fround, crypto_ft_tab,, 2 ENDPROC(__aes_arm_encrypt) .align 5 |