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Date: Fri, 9 Sep 2016 18:19:36 +0800
From: xiakaixu <xiakaixu@...wei.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
CC: <davem@...emloft.net>, <tytso@....edu>, <jaegeuk@...nel.org>,
<nhorman@...driver.com>, <ard.biesheuvel@...aro.org>, <mh1@....fi>,
<linux-crypto@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
Bintian <bintian.wang@...wei.com>, <liushuoran@...wei.com>,
Huxinwei <huxinwei@...wei.com>, <zhangzhibin.zhang@...wei.com>
Subject: Re: Kernel panic - encryption/decryption failed when open file on
Arm64
Hi,
After a deeply research about this crash, seems it is a specific
bug that only exists in armv8 board. And it occurs in this function
in arch/arm64/crypto/aes-glue.c.
static int ctr_encrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
struct scatterlist *src, unsigned int nbytes)
{
...
desc->flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
blkcipher_walk_init(&walk, dst, src, nbytes);
err = blkcipher_walk_virt_block(desc, &walk, AES_BLOCK_SIZE); ---> page allocation failed
...
while ((blocks = (walk.nbytes / AES_BLOCK_SIZE))) { ----> walk.nbytes = 0, and skip this loop
aes_ctr_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
(u8 *)ctx->key_enc, rounds, blocks, walk.iv,
first);
...
err = blkcipher_walk_done(desc, &walk,
walk.nbytes % AES_BLOCK_SIZE);
}
if (nbytes) { ----> enter this if() statement
u8 *tdst = walk.dst.virt.addr + blocks * AES_BLOCK_SIZE;
u8 *tsrc = walk.src.virt.addr + blocks * AES_BLOCK_SIZE;
...
aes_ctr_encrypt(tail, tsrc, (u8 *)ctx->key_enc, rounds, ----> the the sencond input parameter is NULL, so crash...
blocks, walk.iv, first);
...
}
...
}
If the page allocation failed in the function blkcipher_walk_virt_block(),
the variable walk.nbytes = 0, so it will skip the while() loop and enter
the if(nbytes) statment. But here the varibale tsrc is NULL and it is also
the sencond input parameter of the function aes_ctr_encrypt()... Kernel Panic...
I have also researched the similar function in other architectures, and
there if(walk.nbytes) is used, not this if(nbytes) statement in the armv8.
so I think this armv8 function ctr_encrypt() should deal with the page
allocation failed situation.
Regards
Kaixu Xia
> On Thu, Sep 08, 2016 at 08:38:43PM +0800, xiakaixu wrote:
>> Hi,
>>
>> I am using the encryption/decryption feature on arm64 board and a kernel
>> panic occurs just when open a file. As the memory size of the board
>> is limited
>> and there are some page allocation failures before the panic.
>>
>> Seems it is a kernel bug from the call trace log.
>>
>> ...
>> - fscrypt_get_encryption_info
>> - get_crypt_info.part.1
>> - validate_user_key.isra.0
>> - derive_aes_gcm_key
>> - crypto_gcm_decrypt
>> - ablk_decrypt
>> - ctr_encrypt
>> - blkcipher_walk_done
>> - blkcipher_walk_next
>> - __get_free_pages
>> ----------------------------------> page allocation failure
>> ...
>> - aes_ctr_encrypt
>> -----------------------------------------> the input parameter is
>> NULL pointer as the page allocation failure
>>
>>
>> The input parameter of function aes_ctr_encrypt() comes from the
>> /struct blkcipher_walk//
>> //walk/, and this variable /walk /is allocated by the function
>> __get_free_pages(). So if this
>> page allocate failed, the input parameter of function
>> aes_ctr_encrypt() will be NULL. The
>> panic will occurs if we don't check the input parameter.
>>
>> Not sure about this and wish to get your opinions!
>
> If the page allocation fails in blkcipher_walk_next it'll simply
> switch over to processing it block by block. so I don't think the
> warning is related to the crash.
>
> Cheers,
>
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