| Message ID | 1521033450-14447-1-git-send-email-s.mesoraca16@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
Am Mittwoch, 14. März 2018, 14:17:30 CET schrieb Salvatore Mesoraca: Hi Salvatore, > if (walk.nbytes) { > - crypto_ctr_crypt_final(&walk, child); > - err = blkcipher_walk_done(desc, &walk, 0); > + err = crypto_ctr_crypt_final(&walk, child); > + err = blkcipher_walk_done(desc, &walk, err); I guess you either want to handle the error from crypto_ctr_crypt_final or do an err |= blkcipher_walk_done. > } > > return err; Ciao Stephan
2018-03-14 14:31 GMT+01:00 Stephan Mueller <smueller@chronox.de>: > Am Mittwoch, 14. März 2018, 14:17:30 CET schrieb Salvatore Mesoraca: > > Hi Salvatore, > >> if (walk.nbytes) { >> - crypto_ctr_crypt_final(&walk, child); >> - err = blkcipher_walk_done(desc, &walk, 0); >> + err = crypto_ctr_crypt_final(&walk, child); >> + err = blkcipher_walk_done(desc, &walk, err); > > I guess you either want to handle the error from crypto_ctr_crypt_final or do > an err |= blkcipher_walk_done. I think that blkcipher_walk_done handles and returns the error for me. Am I wrong? Best regards, Salvatore
Am Mittwoch, 14. März 2018, 14:46:29 CET schrieb Salvatore Mesoraca: Hi Salvatore, > 2018-03-14 14:31 GMT+01:00 Stephan Mueller <smueller@chronox.de>: > > Am Mittwoch, 14. März 2018, 14:17:30 CET schrieb Salvatore Mesoraca: > > > > Hi Salvatore, > > > >> if (walk.nbytes) { > >> > >> - crypto_ctr_crypt_final(&walk, child); > >> - err = blkcipher_walk_done(desc, &walk, 0); > >> + err = crypto_ctr_crypt_final(&walk, child); > >> + err = blkcipher_walk_done(desc, &walk, err); > > > > I guess you either want to handle the error from crypto_ctr_crypt_final or > > do an err |= blkcipher_walk_done. > > I think that blkcipher_walk_done handles and returns the error for me. > Am I wrong? You are right as you want to finalize the crypto operation even though the encryption fails. Please disregard my comment. > > Best regards, > > Salvatore Ciao Stephan
On Wed, Mar 14, 2018 at 02:17:30PM +0100, Salvatore Mesoraca wrote: > All ciphers implemented in Linux have a block size less than or > equal to 16 bytes and the most demanding hw require 16 bits > alignment for the block buffer. > We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits > alignment, unless the architecture support efficient unaligned > accesses. > We also check, at runtime, that our assumptions still stand, > possibly dynamically allocating a new buffer, just in case > something changes in the future. > > [1] https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com> > --- > > Notes: > Can we maybe skip the runtime check? > > crypto/ctr.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- > 1 file changed, 42 insertions(+), 8 deletions(-) > > diff --git a/crypto/ctr.c b/crypto/ctr.c > index 854d924..f37adf0 100644 > --- a/crypto/ctr.c > +++ b/crypto/ctr.c > @@ -35,6 +35,16 @@ struct crypto_rfc3686_req_ctx { > struct skcipher_request subreq CRYPTO_MINALIGN_ATTR; > }; > > +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS > +#define DECLARE_CIPHER_BUFFER(name) u8 name[16] > +#else > +#define DECLARE_CIPHER_BUFFER(name) u8 __aligned(16) name[16] > +#endif > + > +#define CHECK_CIPHER_BUFFER(name, size, align) \ > + likely(size <= sizeof(name) && \ > + name == PTR_ALIGN(((u8 *) name), align + 1)) > + > static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, > unsigned int keylen) > { > @@ -52,22 +62,35 @@ static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, > return err; > } > > -static void crypto_ctr_crypt_final(struct blkcipher_walk *walk, > - struct crypto_cipher *tfm) > +static int crypto_ctr_crypt_final(struct blkcipher_walk *walk, > + struct crypto_cipher *tfm) > { > unsigned int bsize = crypto_cipher_blocksize(tfm); > unsigned long alignmask = crypto_cipher_alignmask(tfm); > u8 *ctrblk = walk->iv; > - u8 tmp[bsize + alignmask]; > - u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); > u8 *src = walk->src.virt.addr; > u8 *dst = walk->dst.virt.addr; > unsigned int nbytes = walk->nbytes; > + DECLARE_CIPHER_BUFFER(tmp); > + u8 *keystream, *tmp2; > + > + if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask)) > + keystream = tmp; > + else { > + tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC); > + if (!tmp2) > + return -ENOMEM; > + keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1); > + } > > crypto_cipher_encrypt_one(tfm, keystream, ctrblk); > crypto_xor_cpy(dst, keystream, src, nbytes); > > crypto_inc(ctrblk, bsize); > + > + if (unlikely(keystream != tmp)) > + kfree(tmp2); > + return 0; > } This seems silly; isn't the !CHECK_CIPHER_BUFFER() case unreachable? Did you even test it? If there's going to be limits, the crypto API ought to enforce them when registering an algorithm. A better alternative may be to move the keystream buffer into the request context, which is allowed to be variable length. It looks like that would require converting the ctr template over to the skcipher API, since the blkcipher API doesn't have a request context. But my understanding is that that will need to be done eventually anyway, since the blkcipher (and ablkcipher) API is going away. I converted a bunch of algorithms recently and I can look at the remaining ones in crypto/*.c if no one else gets to it first, but it may be a little while until I have time. Also, I recall there being a long discussion a while back about how __aligned(16) doesn't work on local variables because the kernel's stack pointer isn't guaranteed to maintain the alignment assumed by the compiler (see commit b8fbe71f7535)... Eric
2018-03-14 19:31 GMT+01:00 Eric Biggers <ebiggers3@gmail.com>: > On Wed, Mar 14, 2018 at 02:17:30PM +0100, Salvatore Mesoraca wrote: >> All ciphers implemented in Linux have a block size less than or >> equal to 16 bytes and the most demanding hw require 16 bits >> alignment for the block buffer. >> We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits >> alignment, unless the architecture support efficient unaligned >> accesses. >> We also check, at runtime, that our assumptions still stand, >> possibly dynamically allocating a new buffer, just in case >> something changes in the future. >> >> [1] https://lkml.org/lkml/2018/3/7/621 >> >> Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com> >> --- >> >> Notes: >> Can we maybe skip the runtime check? >> >> crypto/ctr.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- >> 1 file changed, 42 insertions(+), 8 deletions(-) >> >> diff --git a/crypto/ctr.c b/crypto/ctr.c >> index 854d924..f37adf0 100644 >> --- a/crypto/ctr.c >> +++ b/crypto/ctr.c >> @@ -35,6 +35,16 @@ struct crypto_rfc3686_req_ctx { >> struct skcipher_request subreq CRYPTO_MINALIGN_ATTR; >> }; >> >> +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS >> +#define DECLARE_CIPHER_BUFFER(name) u8 name[16] >> +#else >> +#define DECLARE_CIPHER_BUFFER(name) u8 __aligned(16) name[16] >> +#endif >> + >> +#define CHECK_CIPHER_BUFFER(name, size, align) \ >> + likely(size <= sizeof(name) && \ >> + name == PTR_ALIGN(((u8 *) name), align + 1)) >> + >> static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, >> unsigned int keylen) >> { >> @@ -52,22 +62,35 @@ static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, >> return err; >> } >> >> -static void crypto_ctr_crypt_final(struct blkcipher_walk *walk, >> - struct crypto_cipher *tfm) >> +static int crypto_ctr_crypt_final(struct blkcipher_walk *walk, >> + struct crypto_cipher *tfm) >> { >> unsigned int bsize = crypto_cipher_blocksize(tfm); >> unsigned long alignmask = crypto_cipher_alignmask(tfm); >> u8 *ctrblk = walk->iv; >> - u8 tmp[bsize + alignmask]; >> - u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); >> u8 *src = walk->src.virt.addr; >> u8 *dst = walk->dst.virt.addr; >> unsigned int nbytes = walk->nbytes; >> + DECLARE_CIPHER_BUFFER(tmp); >> + u8 *keystream, *tmp2; >> + >> + if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask)) >> + keystream = tmp; >> + else { >> + tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC); >> + if (!tmp2) >> + return -ENOMEM; >> + keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1); >> + } >> >> crypto_cipher_encrypt_one(tfm, keystream, ctrblk); >> crypto_xor_cpy(dst, keystream, src, nbytes); >> >> crypto_inc(ctrblk, bsize); >> + >> + if (unlikely(keystream != tmp)) >> + kfree(tmp2); >> + return 0; >> } > > This seems silly; isn't the !CHECK_CIPHER_BUFFER() case unreachable? Did you > even test it? If there's going to be limits, the crypto API ought to enforce > them when registering an algorithm. Yes, as I wrote in the commit log, I put that code just in case something changes (i.e. someone adds a cipher with a bigger block size), so that it won't fail but just work as is. Although I didn't really like it, hence the note. > A better alternative may be to move the keystream buffer into the request > context, which is allowed to be variable length. It looks like that would > require converting the ctr template over to the skcipher API, since the > blkcipher API doesn't have a request context. But my understanding is that that > will need to be done eventually anyway, since the blkcipher (and ablkcipher) API > is going away. I converted a bunch of algorithms recently and I can look at the > remaining ones in crypto/*.c if no one else gets to it first, but it may be a > little while until I have time. This seems much better. I don't think that removing these VLAs is urgent, after all their sizes are limited and not under user control: we can just wait. I might help porting some crypto/*.c to skcipher API. > Also, I recall there being a long discussion a while back about how > __aligned(16) doesn't work on local variables because the kernel's stack pointer > isn't guaranteed to maintain the alignment assumed by the compiler (see commit > b8fbe71f7535)... Oh... didn't know this! Interesting... Thank you for your time, Salvatore
On Wed, Mar 14, 2018 at 02:17:30PM +0100, Salvatore Mesoraca wrote: > All ciphers implemented in Linux have a block size less than or > equal to 16 bytes and the most demanding hw require 16 bits > alignment for the block buffer. > We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits > alignment, unless the architecture support efficient unaligned > accesses. > We also check, at runtime, that our assumptions still stand, > possibly dynamically allocating a new buffer, just in case > something changes in the future. Please move the check to ctr instance creation time. That is, if the underlying blocksize is greater than 16 bytes than simply fail the creation. Thanks,
2018-03-15 10:54 GMT+01:00 Herbert Xu <herbert@gondor.apana.org.au>: > On Wed, Mar 14, 2018 at 02:17:30PM +0100, Salvatore Mesoraca wrote: >> All ciphers implemented in Linux have a block size less than or >> equal to 16 bytes and the most demanding hw require 16 bits >> alignment for the block buffer. >> We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits >> alignment, unless the architecture support efficient unaligned >> accesses. >> We also check, at runtime, that our assumptions still stand, >> possibly dynamically allocating a new buffer, just in case >> something changes in the future. > > Please move the check to ctr instance creation time. That is, > if the underlying blocksize is greater than 16 bytes than simply > fail the creation. Good, I'll send a v2. Thank you for your help, Salvatore
From: Eric Biggers > Sent: 14 March 2018 18:32 ... > Also, I recall there being a long discussion a while back about how > __aligned(16) doesn't work on local variables because the kernel's stack pointer > isn't guaranteed to maintain the alignment assumed by the compiler (see commit > b8fbe71f7535)... ISTR that gcc arbitrarily decided that the x86 stack (for 32 bit) would be kept aligned to more than 4 bytes (16??) - probably so that xmm registers could be written to stack locations. This was a massive ABI change that they didn't tell anyone about! While gcc compiled code maintained the alignment a lot of asm code didn't. I don't know about Linux, but NetBSD didn't even align user stacks. There is a gcc option to not assume that the stack is 'appropriately aligned', but ISTR that it generates rather more code that one might have wished. If the compiler does align the stack, it does so by generating a double stack frame - not pretty at all. David
Hi Salvatore,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v4.16-rc5 next-20180314]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Salvatore-Mesoraca/crypto-ctr-avoid-VLA-use/20180315-213008
config: x86_64-randconfig-x014-201810 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64
Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
All warnings (new ones prefixed by >>):
crypto/ctr.c: In function 'crypto_ctr_crypt':
>> crypto/ctr.c:156:3: warning: 'tmp2' may be used uninitialized in this function [-Wmaybe-uninitialized]
kfree(tmp2);
^~~~~~~~~~~
crypto/ctr.c:133:18: note: 'tmp2' was declared here
u8 *keystream, *tmp2;
^~~~
vim +/tmp2 +156 crypto/ctr.c
121
122 static int crypto_ctr_crypt_inplace(struct blkcipher_walk *walk,
123 struct crypto_cipher *tfm)
124 {
125 void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
126 crypto_cipher_alg(tfm)->cia_encrypt;
127 unsigned int bsize = crypto_cipher_blocksize(tfm);
128 unsigned long alignmask = crypto_cipher_alignmask(tfm);
129 unsigned int nbytes = walk->nbytes;
130 u8 *ctrblk = walk->iv;
131 u8 *src = walk->src.virt.addr;
132 DECLARE_CIPHER_BUFFER(tmp);
133 u8 *keystream, *tmp2;
134
135 if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask))
136 keystream = tmp;
137 else {
138 tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC);
139 if (!tmp2)
140 return -ENOMEM;
141 keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1);
142 }
143
144 do {
145 /* create keystream */
146 fn(crypto_cipher_tfm(tfm), keystream, ctrblk);
147 crypto_xor(src, keystream, bsize);
148
149 /* increment counter in counterblock */
150 crypto_inc(ctrblk, bsize);
151
152 src += bsize;
153 } while ((nbytes -= bsize) >= bsize);
154
155 if (unlikely(keystream != tmp))
> 156 kfree(tmp2);
157 return nbytes;
158 }
159
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
diff --git a/crypto/ctr.c b/crypto/ctr.c index 854d924..f37adf0 100644 --- a/crypto/ctr.c +++ b/crypto/ctr.c @@ -35,6 +35,16 @@ struct crypto_rfc3686_req_ctx { struct skcipher_request subreq CRYPTO_MINALIGN_ATTR; }; +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS +#define DECLARE_CIPHER_BUFFER(name) u8 name[16] +#else +#define DECLARE_CIPHER_BUFFER(name) u8 __aligned(16) name[16] +#endif + +#define CHECK_CIPHER_BUFFER(name, size, align) \ + likely(size <= sizeof(name) && \ + name == PTR_ALIGN(((u8 *) name), align + 1)) + static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, unsigned int keylen) { @@ -52,22 +62,35 @@ static int crypto_ctr_setkey(struct crypto_tfm *parent, const u8 *key, return err; } -static void crypto_ctr_crypt_final(struct blkcipher_walk *walk, - struct crypto_cipher *tfm) +static int crypto_ctr_crypt_final(struct blkcipher_walk *walk, + struct crypto_cipher *tfm) { unsigned int bsize = crypto_cipher_blocksize(tfm); unsigned long alignmask = crypto_cipher_alignmask(tfm); u8 *ctrblk = walk->iv; - u8 tmp[bsize + alignmask]; - u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); u8 *src = walk->src.virt.addr; u8 *dst = walk->dst.virt.addr; unsigned int nbytes = walk->nbytes; + DECLARE_CIPHER_BUFFER(tmp); + u8 *keystream, *tmp2; + + if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask)) + keystream = tmp; + else { + tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC); + if (!tmp2) + return -ENOMEM; + keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1); + } crypto_cipher_encrypt_one(tfm, keystream, ctrblk); crypto_xor_cpy(dst, keystream, src, nbytes); crypto_inc(ctrblk, bsize); + + if (unlikely(keystream != tmp)) + kfree(tmp2); + return 0; } static int crypto_ctr_crypt_segment(struct blkcipher_walk *walk, @@ -106,8 +129,17 @@ static int crypto_ctr_crypt_inplace(struct blkcipher_walk *walk, unsigned int nbytes = walk->nbytes; u8 *ctrblk = walk->iv; u8 *src = walk->src.virt.addr; - u8 tmp[bsize + alignmask]; - u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1); + DECLARE_CIPHER_BUFFER(tmp); + u8 *keystream, *tmp2; + + if (CHECK_CIPHER_BUFFER(tmp, bsize, alignmask)) + keystream = tmp; + else { + tmp2 = kmalloc(bsize + alignmask, GFP_ATOMIC); + if (!tmp2) + return -ENOMEM; + keystream = PTR_ALIGN(tmp2 + 0, alignmask + 1); + } do { /* create keystream */ @@ -120,6 +152,8 @@ static int crypto_ctr_crypt_inplace(struct blkcipher_walk *walk, src += bsize; } while ((nbytes -= bsize) >= bsize); + if (unlikely(keystream != tmp)) + kfree(tmp2); return nbytes; } @@ -147,8 +181,8 @@ static int crypto_ctr_crypt(struct blkcipher_desc *desc, } if (walk.nbytes) { - crypto_ctr_crypt_final(&walk, child); - err = blkcipher_walk_done(desc, &walk, 0); + err = crypto_ctr_crypt_final(&walk, child); + err = blkcipher_walk_done(desc, &walk, err); } return err;
All ciphers implemented in Linux have a block size less than or equal to 16 bytes and the most demanding hw require 16 bits alignment for the block buffer. We avoid 2 VLAs[1] by always allocating 16 bytes with 16 bits alignment, unless the architecture support efficient unaligned accesses. We also check, at runtime, that our assumptions still stand, possibly dynamically allocating a new buffer, just in case something changes in the future. [1] https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com> --- Notes: Can we maybe skip the runtime check? crypto/ctr.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 8 deletions(-)