When the source and destination addresses for the cipher are the same, we
will get a NULL dereference from accessing the split destination
scatterlist memories, as shown:

[   56.565719] tcrypt:
[   56.565719] testing speed of async ecb(aes) (hisi_sec_aes_ecb) encryption
[   56.574683] tcrypt: test 0 (128 bit key, 16 byte blocks):
[   56.587585] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[   56.596361] Mem abort info:
[   56.599151]   ESR = 0x96000006
[   56.602196]   Exception class = DABT (current EL), IL = 32 bits
[   56.608105]   SET = 0, FnV = 0
[   56.611149]   EA = 0, S1PTW = 0
[   56.614280] Data abort info:
[   56.617151]   ISV = 0, ISS = 0x00000006
[   56.620976]   CM = 0, WnR = 0
[   56.623930] user pgtable: 4k pages, 48-bit VAs, pgdp = (____ptrval____)
[   56.630533] [0000000000000000] pgd=0000041fc7e4d003, pud=0000041fcd9bf003, pmd=0000000000000000
[   56.639224] Internal error: Oops: 96000006 [#1] PREEMPT SMP
[   56.644782] Modules linked in: tcrypt(+)
[   56.648695] CPU: 21 PID: 2326 Comm: insmod Tainted: G        W         4.19.0-rc6-00001-g3fabfb8-dirty #716
[   56.658420] Hardware name: Huawei Taishan 2280 /D05, BIOS Hisilicon D05 IT17 Nemo 2.0 RC0 10/05/2018
[   56.667537] pstate: 20000005 (nzCv daif -PAN -UAO)
[   56.672322] pc : sec_alg_skcipher_crypto+0x318/0x748
[   56.677274] lr : sec_alg_skcipher_crypto+0x178/0x748
[   56.682224] sp : ffff0000118e3840
[   56.685525] x29: ffff0000118e3840 x28: ffff841fbb3f8118
[   56.690825] x27: 0000000000000000 x26: 0000000000000000
[   56.696125] x25: ffff841fbb3f8080 x24: ffff841fbadc0018
[   56.701425] x23: ffff000009119000 x22: ffff841fbb24e280
[   56.706724] x21: ffff841ff212e780 x20: ffff841ff212e700
[   56.712023] x19: 0000000000000001 x18: ffffffffffffffff
[   56.717322] x17: 0000000000000000 x16: 0000000000000000
[   56.722621] x15: ffff0000091196c8 x14: 72635f7265687069
[   56.727920] x13: 636b735f676c615f x12: ffff000009119940
[   56.733219] x11: 0000000000000000 x10: 00000000006080c0
[   56.738519] x9 : 0000000000000000 x8 : ffff841fbb24e480
[   56.743818] x7 : ffff841fbb24e500 x6 : ffff841ff00cdcc0
[   56.749117] x5 : 0000000000000010 x4 : 0000000000000000
[   56.754416] x3 : ffff841fbb24e380 x2 : ffff841fbb24e480
[   56.759715] x1 : 0000000000000000 x0 : ffff000008f682c8
[   56.765016] Process insmod (pid: 2326, stack limit = 0x(____ptrval____))
[   56.771702] Call trace:
[   56.774136]  sec_alg_skcipher_crypto+0x318/0x748
[   56.778740]  sec_alg_skcipher_encrypt+0x10/0x18
[   56.783259]  test_skcipher_speed+0x2a0/0x700 [tcrypt]
[   56.788298]  do_test+0x18f8/0x48c8 [tcrypt]
[   56.792469]  tcrypt_mod_init+0x60/0x1000 [tcrypt]
[   56.797161]  do_one_initcall+0x5c/0x178
[   56.800985]  do_init_module+0x58/0x1b4
[   56.804721]  load_module+0x1da4/0x2150
[   56.808456]  __se_sys_init_module+0x14c/0x1e8
[   56.812799]  __arm64_sys_init_module+0x18/0x20
[   56.817231]  el0_svc_common+0x60/0xe8
[   56.820880]  el0_svc_handler+0x2c/0x80
[   56.824615]  el0_svc+0x8/0xc
[   56.827483] Code: a94c87a3 910b2000 f87b7842 f9004ba2 (b87b7821)
[   56.833564] ---[ end trace 0f63290590e93d94 ]---
Segmentation fault

Fix this by only accessing these memories when we have different src and
dst.

Fixes: 915e4e84

 ("crypto: hisilicon - SEC security accelerator driver")
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>