[PATCH] ppp: mppe: Remove VLA usage

[PATCH] ppp: mppe: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
VLA) by switching to shash directly and keeping the associated descriptor
allocated with the regular state on the heap.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/net/ppp/ppp_mppe.c | 57 +++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 26 deletions(-)

diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
index 6c7fd98cb00a..5b4b81027a75 100644
--- a/drivers/net/ppp/ppp_mppe.c
+++ b/drivers/net/ppp/ppp_mppe.c
@@ -96,7 +96,7 @@ static inline void sha_pad_init(struct sha_pad *shapad)
  */
 struct ppp_mppe_state {
 	struct crypto_skcipher *arc4;
-	struct crypto_ahash *sha1;
+	struct shash_desc *sha1;
 	unsigned char *sha1_digest;
 	unsigned char master_key[MPPE_MAX_KEY_LEN];
 	unsigned char session_key[MPPE_MAX_KEY_LEN];
@@ -136,25 +136,16 @@ struct ppp_mppe_state {
  */
 static void get_new_key_from_sha(struct ppp_mppe_state * state)
 {
-	AHASH_REQUEST_ON_STACK(req, state->sha1);
-	struct scatterlist sg[4];
-	unsigned int nbytes;
-
-	sg_init_table(sg, 4);
-
-	nbytes = setup_sg(&sg[0], state->master_key, state->keylen);
-	nbytes += setup_sg(&sg[1], sha_pad->sha_pad1,
-			   sizeof(sha_pad->sha_pad1));
-	nbytes += setup_sg(&sg[2], state->session_key, state->keylen);
-	nbytes += setup_sg(&sg[3], sha_pad->sha_pad2,
-			   sizeof(sha_pad->sha_pad2));
-
-	ahash_request_set_tfm(req, state->sha1);
-	ahash_request_set_callback(req, 0, NULL, NULL);
-	ahash_request_set_crypt(req, sg, state->sha1_digest, nbytes);
-
-	crypto_ahash_digest(req);
-	ahash_request_zero(req);
+	crypto_shash_init(state->sha1);
+	crypto_shash_update(state->sha1, state->master_key,
+			    state->keylen);
+	crypto_shash_update(state->sha1, sha_pad->sha_pad1,
+			    sizeof(sha_pad->sha_pad1));
+	crypto_shash_update(state->sha1, state->session_key,
+			    state->keylen);
+	crypto_shash_update(state->sha1, sha_pad->sha_pad2,
+			    sizeof(sha_pad->sha_pad2));
+	crypto_shash_final(state->sha1, state->sha1_digest);
 }
 
 /*
@@ -200,6 +191,7 @@ static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
 static void *mppe_alloc(unsigned char *options, int optlen)
 {
 	struct ppp_mppe_state *state;
+	struct crypto_shash *shash;
 	unsigned int digestsize;
 
 	if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
@@ -217,13 +209,21 @@ static void *mppe_alloc(unsigned char *options, int optlen)
 		goto out_free;
 	}
 
-	state->sha1 = crypto_alloc_ahash("sha1", 0, CRYPTO_ALG_ASYNC);
-	if (IS_ERR(state->sha1)) {
-		state->sha1 = NULL;
+	shash = crypto_alloc_shash("sha1", 0, 0);
+	if (IS_ERR(shash))
+		goto out_free;
+
+	state->sha1 = kmalloc(sizeof(*state->sha1) +
+				     crypto_shash_descsize(shash),
+			      GFP_KERNEL);
+	if (!state->sha1) {
+		crypto_free_shash(shash);
 		goto out_free;
 	}
+	state->sha1->tfm = shash;
+	state->sha1->flags = 0;
 
-	digestsize = crypto_ahash_digestsize(state->sha1);
+	digestsize = crypto_shash_digestsize(shash);
 	if (digestsize < MPPE_MAX_KEY_LEN)
 		goto out_free;
 
@@ -246,7 +246,11 @@ static void *mppe_alloc(unsigned char *options, int optlen)
 
 out_free:
 	kfree(state->sha1_digest);
-	crypto_free_ahash(state->sha1);
+	if (state->sha1) {
+		if (state->sha1->tfm)
+			crypto_free_shash(state->sha1->tfm);
+		kzfree(state->sha1);
+	}
 	crypto_free_skcipher(state->arc4);
 	kfree(state);
 out:
@@ -261,7 +265,8 @@ static void mppe_free(void *arg)
 	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
 	if (state) {
 		kfree(state->sha1_digest);
-		crypto_free_ahash(state->sha1);
+		crypto_free_shash(state->sha1->tfm);
+		kzfree(state->sha1);
 		crypto_free_skcipher(state->arc4);
 		kfree(state);
 	}
-- 
2.17.1


-- 
Kees Cook
Pixel Security

[PATCH] ppp: mppe: Remove VLA usage

[Kees Cook]

In the quest to remove all stack VLA usage from the kernel[1], this
removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
VLA) by switching to shash directly and keeping the associated descriptor
allocated with the regular state on the heap.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/net/ppp/ppp_mppe.c | 57 +++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 26 deletions(-)

diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
index 6c7fd98cb00a..5b4b81027a75 100644
--- a/drivers/net/ppp/ppp_mppe.c
+++ b/drivers/net/ppp/ppp_mppe.c
@@ -96,7 +96,7 @@ static inline void sha_pad_init(struct sha_pad *shapad)
  */
 struct ppp_mppe_state {
 	struct crypto_skcipher *arc4;
-	struct crypto_ahash *sha1;
+	struct shash_desc *sha1;
 	unsigned char *sha1_digest;
 	unsigned char master_key[MPPE_MAX_KEY_LEN];
 	unsigned char session_key[MPPE_MAX_KEY_LEN];
@@ -136,25 +136,16 @@ struct ppp_mppe_state {
  */
 static void get_new_key_from_sha(struct ppp_mppe_state * state)
 {
-	AHASH_REQUEST_ON_STACK(req, state->sha1);
-	struct scatterlist sg[4];
-	unsigned int nbytes;
-
-	sg_init_table(sg, 4);
-
-	nbytes = setup_sg(&sg[0], state->master_key, state->keylen);
-	nbytes += setup_sg(&sg[1], sha_pad->sha_pad1,
-			   sizeof(sha_pad->sha_pad1));
-	nbytes += setup_sg(&sg[2], state->session_key, state->keylen);
-	nbytes += setup_sg(&sg[3], sha_pad->sha_pad2,
-			   sizeof(sha_pad->sha_pad2));
-
-	ahash_request_set_tfm(req, state->sha1);
-	ahash_request_set_callback(req, 0, NULL, NULL);
-	ahash_request_set_crypt(req, sg, state->sha1_digest, nbytes);
-
-	crypto_ahash_digest(req);
-	ahash_request_zero(req);
+	crypto_shash_init(state->sha1);
+	crypto_shash_update(state->sha1, state->master_key,
+			    state->keylen);
+	crypto_shash_update(state->sha1, sha_pad->sha_pad1,
+			    sizeof(sha_pad->sha_pad1));
+	crypto_shash_update(state->sha1, state->session_key,
+			    state->keylen);
+	crypto_shash_update(state->sha1, sha_pad->sha_pad2,
+			    sizeof(sha_pad->sha_pad2));
+	crypto_shash_final(state->sha1, state->sha1_digest);
 }
 
 /*
@@ -200,6 +191,7 @@ static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
 static void *mppe_alloc(unsigned char *options, int optlen)
 {
 	struct ppp_mppe_state *state;
+	struct crypto_shash *shash;
 	unsigned int digestsize;
 
 	if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
@@ -217,13 +209,21 @@ static void *mppe_alloc(unsigned char *options, int optlen)
 		goto out_free;
 	}
 
-	state->sha1 = crypto_alloc_ahash("sha1", 0, CRYPTO_ALG_ASYNC);
-	if (IS_ERR(state->sha1)) {
-		state->sha1 = NULL;
+	shash = crypto_alloc_shash("sha1", 0, 0);
+	if (IS_ERR(shash))
+		goto out_free;
+
+	state->sha1 = kmalloc(sizeof(*state->sha1) +
+				     crypto_shash_descsize(shash),
+			      GFP_KERNEL);
+	if (!state->sha1) {
+		crypto_free_shash(shash);
 		goto out_free;
 	}
+	state->sha1->tfm = shash;
+	state->sha1->flags = 0;
 
-	digestsize = crypto_ahash_digestsize(state->sha1);
+	digestsize = crypto_shash_digestsize(shash);
 	if (digestsize < MPPE_MAX_KEY_LEN)
 		goto out_free;
 
@@ -246,7 +246,11 @@ static void *mppe_alloc(unsigned char *options, int optlen)
 
 out_free:
 	kfree(state->sha1_digest);
-	crypto_free_ahash(state->sha1);
+	if (state->sha1) {
+		if (state->sha1->tfm)
+			crypto_free_shash(state->sha1->tfm);
+		kzfree(state->sha1);
+	}
 	crypto_free_skcipher(state->arc4);
 	kfree(state);
 out:
@@ -261,7 +265,8 @@ static void mppe_free(void *arg)
 	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
 	if (state) {
 		kfree(state->sha1_digest);
-		crypto_free_ahash(state->sha1);
+		crypto_free_shash(state->sha1->tfm);
+		kzfree(state->sha1);
 		crypto_free_skcipher(state->arc4);
 		kfree(state);
 	}
-- 
2.17.1


-- 
Kees Cook
Pixel Security

Re: [PATCH] ppp: mppe: Remove VLA usage

[Arnd Bergmann]

On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@chromium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> VLA) by switching to shash directly and keeping the associated descriptor
> allocated with the regular state on the heap.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

I had concerns at first that this approach might make it slower, but
upon reading through implementation of the shash_ahash_ implementation,
I concluded that it can only be better than before, improving both
performance and stack usage.

Acked-by: Arnd Bergmann <arnd@arndb.de>

Re: [PATCH] ppp: mppe: Remove VLA usage

[Arnd Bergmann]

On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@chromium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> VLA) by switching to shash directly and keeping the associated descriptor
> allocated with the regular state on the heap.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

I had concerns at first that this approach might make it slower, but
upon reading through implementation of the shash_ahash_ implementation,
I concluded that it can only be better than before, improving both
performance and stack usage.

Acked-by: Arnd Bergmann <arnd@arndb.de>

Re: [PATCH] ppp: mppe: Remove VLA usage

[Eric Biggers]

On Sun, Jul 15, 2018 at 09:05:16PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> VLA) by switching to shash directly and keeping the associated descriptor
> allocated with the regular state on the heap.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/net/ppp/ppp_mppe.c | 57 +++++++++++++++++++++-----------------
>  1 file changed, 31 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
> index 6c7fd98cb00a..5b4b81027a75 100644
> --- a/drivers/net/ppp/ppp_mppe.c
> +++ b/drivers/net/ppp/ppp_mppe.c
> @@ -96,7 +96,7 @@ static inline void sha_pad_init(struct sha_pad *shapad)
>   */
>  struct ppp_mppe_state {
>  	struct crypto_skcipher *arc4;
> -	struct crypto_ahash *sha1;
> +	struct shash_desc *sha1;
>  	unsigned char *sha1_digest;
>  	unsigned char master_key[MPPE_MAX_KEY_LEN];
>  	unsigned char session_key[MPPE_MAX_KEY_LEN];
> @@ -136,25 +136,16 @@ struct ppp_mppe_state {
>   */
>  static void get_new_key_from_sha(struct ppp_mppe_state * state)
>  {
> -	AHASH_REQUEST_ON_STACK(req, state->sha1);
> -	struct scatterlist sg[4];
> -	unsigned int nbytes;
> -
> -	sg_init_table(sg, 4);
> -
> -	nbytes = setup_sg(&sg[0], state->master_key, state->keylen);
> -	nbytes += setup_sg(&sg[1], sha_pad->sha_pad1,
> -			   sizeof(sha_pad->sha_pad1));
> -	nbytes += setup_sg(&sg[2], state->session_key, state->keylen);
> -	nbytes += setup_sg(&sg[3], sha_pad->sha_pad2,
> -			   sizeof(sha_pad->sha_pad2));
> -
> -	ahash_request_set_tfm(req, state->sha1);
> -	ahash_request_set_callback(req, 0, NULL, NULL);
> -	ahash_request_set_crypt(req, sg, state->sha1_digest, nbytes);
> -
> -	crypto_ahash_digest(req);
> -	ahash_request_zero(req);
> +	crypto_shash_init(state->sha1);
> +	crypto_shash_update(state->sha1, state->master_key,
> +			    state->keylen);
> +	crypto_shash_update(state->sha1, sha_pad->sha_pad1,
> +			    sizeof(sha_pad->sha_pad1));
> +	crypto_shash_update(state->sha1, state->session_key,
> +			    state->keylen);
> +	crypto_shash_update(state->sha1, sha_pad->sha_pad2,
> +			    sizeof(sha_pad->sha_pad2));
> +	crypto_shash_final(state->sha1, state->sha1_digest);
>  }
>  
>  /*
> @@ -200,6 +191,7 @@ static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
>  static void *mppe_alloc(unsigned char *options, int optlen)
>  {
>  	struct ppp_mppe_state *state;
> +	struct crypto_shash *shash;
>  	unsigned int digestsize;
>  
>  	if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
> @@ -217,13 +209,21 @@ static void *mppe_alloc(unsigned char *options, int optlen)
>  		goto out_free;
>  	}
>  
> -	state->sha1 = crypto_alloc_ahash("sha1", 0, CRYPTO_ALG_ASYNC);
> -	if (IS_ERR(state->sha1)) {
> -		state->sha1 = NULL;
> +	shash = crypto_alloc_shash("sha1", 0, 0);
> +	if (IS_ERR(shash))
> +		goto out_free;
> +
> +	state->sha1 = kmalloc(sizeof(*state->sha1) +
> +				     crypto_shash_descsize(shash),
> +			      GFP_KERNEL);
> +	if (!state->sha1) {
> +		crypto_free_shash(shash);
>  		goto out_free;
>  	}
> +	state->sha1->tfm = shash;
> +	state->sha1->flags = 0;
>  
> -	digestsize = crypto_ahash_digestsize(state->sha1);
> +	digestsize = crypto_shash_digestsize(shash);
>  	if (digestsize < MPPE_MAX_KEY_LEN)
>  		goto out_free;
>  
> @@ -246,7 +246,11 @@ static void *mppe_alloc(unsigned char *options, int optlen)
>  
>  out_free:
>  	kfree(state->sha1_digest);
> -	crypto_free_ahash(state->sha1);
> +	if (state->sha1) {
> +		if (state->sha1->tfm)
> +			crypto_free_shash(state->sha1->tfm);

It's not necessary to check for NULL before calling crypto_free_shash().
Otherwise this looks good, though I dislike how the error codes aren't checked
in get_new_key_from_sha() (of course, they weren't before this patch either).

> +		kzfree(state->sha1);
> +	}
>  	crypto_free_skcipher(state->arc4);
>  	kfree(state);
>  out:
> @@ -261,7 +265,8 @@ static void mppe_free(void *arg)
>  	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
>  	if (state) {
>  		kfree(state->sha1_digest);
> -		crypto_free_ahash(state->sha1);
> +		crypto_free_shash(state->sha1->tfm);
> +		kzfree(state->sha1);
>  		crypto_free_skcipher(state->arc4);
>  		kfree(state);
>  	}
> -- 
> 2.17.1
> 
> 
> -- 
> Kees Cook
> Pixel Security

Re: [PATCH] ppp: mppe: Remove VLA usage

[Eric Biggers]

On Sun, Jul 15, 2018 at 09:05:16PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> VLA) by switching to shash directly and keeping the associated descriptor
> allocated with the regular state on the heap.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/net/ppp/ppp_mppe.c | 57 +++++++++++++++++++++-----------------
>  1 file changed, 31 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
> index 6c7fd98cb00a..5b4b81027a75 100644
> --- a/drivers/net/ppp/ppp_mppe.c
> +++ b/drivers/net/ppp/ppp_mppe.c
> @@ -96,7 +96,7 @@ static inline void sha_pad_init(struct sha_pad *shapad)
>   */
>  struct ppp_mppe_state {
>  	struct crypto_skcipher *arc4;
> -	struct crypto_ahash *sha1;
> +	struct shash_desc *sha1;
>  	unsigned char *sha1_digest;
>  	unsigned char master_key[MPPE_MAX_KEY_LEN];
>  	unsigned char session_key[MPPE_MAX_KEY_LEN];
> @@ -136,25 +136,16 @@ struct ppp_mppe_state {
>   */
>  static void get_new_key_from_sha(struct ppp_mppe_state * state)
>  {
> -	AHASH_REQUEST_ON_STACK(req, state->sha1);
> -	struct scatterlist sg[4];
> -	unsigned int nbytes;
> -
> -	sg_init_table(sg, 4);
> -
> -	nbytes = setup_sg(&sg[0], state->master_key, state->keylen);
> -	nbytes += setup_sg(&sg[1], sha_pad->sha_pad1,
> -			   sizeof(sha_pad->sha_pad1));
> -	nbytes += setup_sg(&sg[2], state->session_key, state->keylen);
> -	nbytes += setup_sg(&sg[3], sha_pad->sha_pad2,
> -			   sizeof(sha_pad->sha_pad2));
> -
> -	ahash_request_set_tfm(req, state->sha1);
> -	ahash_request_set_callback(req, 0, NULL, NULL);
> -	ahash_request_set_crypt(req, sg, state->sha1_digest, nbytes);
> -
> -	crypto_ahash_digest(req);
> -	ahash_request_zero(req);
> +	crypto_shash_init(state->sha1);
> +	crypto_shash_update(state->sha1, state->master_key,
> +			    state->keylen);
> +	crypto_shash_update(state->sha1, sha_pad->sha_pad1,
> +			    sizeof(sha_pad->sha_pad1));
> +	crypto_shash_update(state->sha1, state->session_key,
> +			    state->keylen);
> +	crypto_shash_update(state->sha1, sha_pad->sha_pad2,
> +			    sizeof(sha_pad->sha_pad2));
> +	crypto_shash_final(state->sha1, state->sha1_digest);
>  }
>  
>  /*
> @@ -200,6 +191,7 @@ static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
>  static void *mppe_alloc(unsigned char *options, int optlen)
>  {
>  	struct ppp_mppe_state *state;
> +	struct crypto_shash *shash;
>  	unsigned int digestsize;
>  
>  	if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
> @@ -217,13 +209,21 @@ static void *mppe_alloc(unsigned char *options, int optlen)
>  		goto out_free;
>  	}
>  
> -	state->sha1 = crypto_alloc_ahash("sha1", 0, CRYPTO_ALG_ASYNC);
> -	if (IS_ERR(state->sha1)) {
> -		state->sha1 = NULL;
> +	shash = crypto_alloc_shash("sha1", 0, 0);
> +	if (IS_ERR(shash))
> +		goto out_free;
> +
> +	state->sha1 = kmalloc(sizeof(*state->sha1) +
> +				     crypto_shash_descsize(shash),
> +			      GFP_KERNEL);
> +	if (!state->sha1) {
> +		crypto_free_shash(shash);
>  		goto out_free;
>  	}
> +	state->sha1->tfm = shash;
> +	state->sha1->flags = 0;
>  
> -	digestsize = crypto_ahash_digestsize(state->sha1);
> +	digestsize = crypto_shash_digestsize(shash);
>  	if (digestsize < MPPE_MAX_KEY_LEN)
>  		goto out_free;
>  
> @@ -246,7 +246,11 @@ static void *mppe_alloc(unsigned char *options, int optlen)
>  
>  out_free:
>  	kfree(state->sha1_digest);
> -	crypto_free_ahash(state->sha1);
> +	if (state->sha1) {
> +		if (state->sha1->tfm)
> +			crypto_free_shash(state->sha1->tfm);

It's not necessary to check for NULL before calling crypto_free_shash().
Otherwise this looks good, though I dislike how the error codes aren't checked
in get_new_key_from_sha() (of course, they weren't before this patch either).

> +		kzfree(state->sha1);
> +	}
>  	crypto_free_skcipher(state->arc4);
>  	kfree(state);
>  out:
> @@ -261,7 +265,8 @@ static void mppe_free(void *arg)
>  	struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
>  	if (state) {
>  		kfree(state->sha1_digest);
> -		crypto_free_ahash(state->sha1);
> +		crypto_free_shash(state->sha1->tfm);
> +		kzfree(state->sha1);
>  		crypto_free_skcipher(state->arc4);
>  		kfree(state);
>  	}
> -- 
> 2.17.1
> 
> 
> -- 
> Kees Cook
> Pixel Security

Re: [PATCH] ppp: mppe: Remove VLA usage

[Kees Cook]

On Mon, Jul 16, 2018 at 4:01 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@chromium.org> wrote:
>> In the quest to remove all stack VLA usage from the kernel[1], this
>> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
>> VLA) by switching to shash directly and keeping the associated descriptor
>> allocated with the regular state on the heap.
>>
>> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>
> I had concerns at first that this approach might make it slower, but
> upon reading through implementation of the shash_ahash_ implementation,
> I concluded that it can only be better than before, improving both
> performance and stack usage.
>
> Acked-by: Arnd Bergmann <arnd@arndb.de>

Paul,

Is this something you can take via your tree?

Thanks,

-Kees


-- 
Kees Cook
Pixel Security

Re: [PATCH] ppp: mppe: Remove VLA usage

[Kees Cook]

On Mon, Jul 16, 2018 at 4:01 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@chromium.org> wrote:
>> In the quest to remove all stack VLA usage from the kernel[1], this
>> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
>> VLA) by switching to shash directly and keeping the associated descriptor
>> allocated with the regular state on the heap.
>>
>> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>
> I had concerns at first that this approach might make it slower, but
> upon reading through implementation of the shash_ahash_ implementation,
> I concluded that it can only be better than before, improving both
> performance and stack usage.
>
> Acked-by: Arnd Bergmann <arnd@arndb.de>

Paul,

Is this something you can take via your tree?

Thanks,

-Kees


-- 
Kees Cook
Pixel Security

Re: [PATCH] ppp: mppe: Remove VLA usage

[Paul Mackerras]

On Thu, Aug 02, 2018 at 04:27:01PM -0700, Kees Cook wrote:
> On Mon, Jul 16, 2018 at 4:01 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@chromium.org> wrote:
> >> In the quest to remove all stack VLA usage from the kernel[1], this
> >> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> >> VLA) by switching to shash directly and keeping the associated descriptor
> >> allocated with the regular state on the heap.
> >>
> >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > I had concerns at first that this approach might make it slower, but
> > upon reading through implementation of the shash_ahash_ implementation,
> > I concluded that it can only be better than before, improving both
> > performance and stack usage.
> >
> > Acked-by: Arnd Bergmann <arnd@arndb.de>
> 
> Paul,
> 
> Is this something you can take via your tree?

No, it would go via the netdev tree, I expect.

Paul.

Re: [PATCH] ppp: mppe: Remove VLA usage

[Paul Mackerras]

On Thu, Aug 02, 2018 at 04:27:01PM -0700, Kees Cook wrote:
> On Mon, Jul 16, 2018 at 4:01 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@chromium.org> wrote:
> >> In the quest to remove all stack VLA usage from the kernel[1], this
> >> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> >> VLA) by switching to shash directly and keeping the associated descriptor
> >> allocated with the regular state on the heap.
> >>
> >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> >>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >
> > I had concerns at first that this approach might make it slower, but
> > upon reading through implementation of the shash_ahash_ implementation,
> > I concluded that it can only be better than before, improving both
> > performance and stack usage.
> >
> > Acked-by: Arnd Bergmann <arnd@arndb.de>
> 
> Paul,
> 
> Is this something you can take via your tree?

No, it would go via the netdev tree, I expect.

Paul.