crypto: caam - fix the address of the last entry of S/G

For skcipher algorithms, the input, output HW S/G tables
look like this: [IV, src][dst, IV]
Now, we can have 2 conditions here:
- there is no IV;
- src and dst are equal (in-place encryption) and scattered
and the error is an "off-by-one" in the HW S/G table.

This issue was seen with KASAN:
BUG: KASAN: slab-out-of-bounds in skcipher_edesc_alloc+0x95c/0x1018

Read of size 4 at addr ffff000022a02958 by task cryptomgr_test/321

CPU: 2 PID: 321 Comm: cryptomgr_test Not tainted
5.6.0-rc1-00165-ge4ef8383-dirty #4
Hardware name: LS1046A RDB Board (DT)
Call trace:
 dump_backtrace+0x0/0x260
 show_stack+0x14/0x20
 dump_stack+0xe8/0x144
 print_address_description.isra.11+0x64/0x348
 __kasan_report+0x11c/0x230
 kasan_report+0xc/0x18
 __asan_load4+0x90/0xb0
 skcipher_edesc_alloc+0x95c/0x1018
 skcipher_encrypt+0x84/0x150
 crypto_skcipher_encrypt+0x50/0x68
 test_skcipher_vec_cfg+0x4d4/0xc10
 test_skcipher_vec+0x178/0x1d8
 alg_test_skcipher+0xec/0x230
 alg_test.part.44+0x114/0x4a0
 alg_test+0x1c/0x60
 cryptomgr_test+0x34/0x58
 kthread+0x1b8/0x1c0
 ret_from_fork+0x10/0x18

Allocated by task 321:
 save_stack+0x24/0xb0
 __kasan_kmalloc.isra.10+0xc4/0xe0
 kasan_kmalloc+0xc/0x18
 __kmalloc+0x178/0x2b8
 skcipher_edesc_alloc+0x21c/0x1018
 skcipher_encrypt+0x84/0x150
 crypto_skcipher_encrypt+0x50/0x68
 test_skcipher_vec_cfg+0x4d4/0xc10
 test_skcipher_vec+0x178/0x1d8
 alg_test_skcipher+0xec/0x230
 alg_test.part.44+0x114/0x4a0
 alg_test+0x1c/0x60
 cryptomgr_test+0x34/0x58
 kthread+0x1b8/0x1c0
 ret_from_fork+0x10/0x18

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff000022a02800
 which belongs to the cache dma-kmalloc-512 of size 512
The buggy address is located 344 bytes inside of
 512-byte region [ffff000022a02800, ffff000022a02a00)
The buggy address belongs to the page:
page:fffffe00006a8000 refcount:1 mapcount:0 mapping:ffff00093200c400
index:0x0 compound_mapcount: 0
flags: 0xffff00000010200(slab|head)
raw: 0ffff00000010200 dead000000000100 dead000000000122 ffff00093200c400
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff000022a02800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff000022a02880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff000022a02900: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
                                                    ^
 ffff000022a02980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff000022a02a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

Fixes: 334d37c ("crypto: caam - update IV using HW support")
Cc: <[email protected]> # v5.3+
Signed-off-by: Iuliana Prodan <[email protected]>
Reviewed-by: Horia Geantă <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

drivers/crypto/caam/caamalg.c

@@ -1715,7 +1715,7 @@ static struct skcipher_edesc *skcipher_edesc_alloc(struct skcipher_request *req,
 
 	if (ivsize || mapped_dst_nents > 1)
 		sg_to_sec4_set_last(edesc->sec4_sg + dst_sg_idx +
-				    mapped_dst_nents);
+				    mapped_dst_nents - 1 + !!ivsize);
 
 	if (sec4_sg_bytes) {
 		edesc->sec4_sg_dma = dma_map_single(jrdev, edesc->sec4_sg,