LinuxLists.cc - [PATCH] crypto: ccp - avoid uninitialized variable warning

2017-07-31 20:49:58

Subject: [PATCH] crypto: ccp - avoid uninitialized variable warning

The added support for version 5 CCPs introduced a false-positive
warning in the RSA implementation:

drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This changes the code in a way that should make it easier for
the compiler to track the state of the sb_count variable, and
avoid the warning.

Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5 CCPs")
Signed-off-by: Arnd Bergmann <[email protected]>
---
drivers/crypto/ccp/ccp-ops.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
index 40c062ad8726..a8bc207b099a 100644
--- a/drivers/crypto/ccp/ccp-ops.c
+++ b/drivers/crypto/ccp/ccp-ops.c
@@ -1758,6 +1758,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, struct ccp_cmd *cmd)
o_len = 32 * ((rsa->key_size + 255) / 256);
i_len = o_len * 2;

+ sb_count = 0;
if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
/* sb_count is the number of storage block slots required
* for the modulus.
@@ -1852,7 +1853,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, struct ccp_cmd *cmd)
ccp_dm_free(&exp);

e_sb:
- if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
+ if (sb_count)
cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key, sb_count);

return ret;
--
2.9.0

2017-08-01 14:53:22

by Gary R Hook

[permalink] [raw]

Subject: Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

On 07/31/2017 03:49 PM, Arnd Bergmann wrote:
> The added support for version 5 CCPs introduced a false-positive
> warning in the RSA implementation:
>
> drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
> drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> This changes the code in a way that should make it easier for
> the compiler to track the state of the sb_count variable, and
> avoid the warning.
>
> Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5 CCPs")
> Signed-off-by: Arnd Bergmann <[email protected]>
> ---
> drivers/crypto/ccp/ccp-ops.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
> index 40c062ad8726..a8bc207b099a 100644
> --- a/drivers/crypto/ccp/ccp-ops.c
> +++ b/drivers/crypto/ccp/ccp-ops.c
> @@ -1758,6 +1758,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, struct ccp_cmd *cmd)
> o_len = 32 * ((rsa->key_size + 255) / 256);
> i_len = o_len * 2;
>
> + sb_count = 0;
> if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
> /* sb_count is the number of storage block slots required
> * for the modulus.
> @@ -1852,7 +1853,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, struct ccp_cmd *cmd)
> ccp_dm_free(&exp);
>
> e_sb:
> - if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
> + if (sb_count)
> cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key, sb_count);
>
> return ret;
>

This is a fine solution. However, having lived with this annoyance for a
while, and even hoping that a
a later compiler fixes it, I would have preferred to either:

1) Initialize the local variable at declaration time, or

2) Use this patch, which the compiler could optimize as it sees fit, and
maintains a clear distinction
for the code path for older devices:

diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
index 40c062a..a3a884a 100644
--- a/drivers/crypto/ccp/ccp-ops.c
+++ b/drivers/crypto/ccp/ccp-ops.c
@@ -1733,7 +1733,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
*cmd_q, struct ccp_cmd *cmd)
struct ccp_rsa_engine *rsa = &cmd->u.rsa;
struct ccp_dm_workarea exp, src, dst;
struct ccp_op op;
- unsigned int sb_count, i_len, o_len;
+ unsigned int i_len, o_len;
int ret;

/* Check against the maximum allowable size, in bits */
@@ -1762,7 +1762,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
*cmd_q, struct ccp_cmd *cmd)
/* sb_count is the number of storage block slots required
* for the modulus.
*/
- sb_count = o_len / CCP_SB_BYTES;
+ unsigned int sb_count = o_len / CCP_SB_BYTES;
op.sb_key = cmd_q->ccp->vdata->perform->sballoc(cmd_q,
sb_count);
if (!op.sb_key)
@@ -1853,7 +1853,10 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
*cmd_q, struct ccp_cmd *cmd)

e_sb:
if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
+ {
+ unsigned int sb_count = o_len / CCP_SB_BYTES;
cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key,
sb_count);
+ }

return ret;
}

Discuss?

2017-08-01 20:35:42

by Arnd Bergmann

[permalink] [raw]

Subject: Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

On Tue, Aug 1, 2017 at 4:52 PM, Gary R Hook <[email protected]> wrote:
> On 07/31/2017 03:49 PM, Arnd Bergmann wrote:
>>
>> The added support for version 5 CCPs introduced a false-positive
>> warning in the RSA implementation:
>>
>> drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
>> drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used
>> uninitialized in this function [-Werror=maybe-uninitialized]
>>
>> This changes the code in a way that should make it easier for
>> the compiler to track the state of the sb_count variable, and
>> avoid the warning.
>>
>> Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5
>> CCPs")
>> Signed-off-by: Arnd Bergmann <[email protected]>
>> ---
>> drivers/crypto/ccp/ccp-ops.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
>> index 40c062ad8726..a8bc207b099a 100644
>> --- a/drivers/crypto/ccp/ccp-ops.c
>> +++ b/drivers/crypto/ccp/ccp-ops.c
>> @@ -1758,6 +1758,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
>> *cmd_q, struct ccp_cmd *cmd)
>> o_len = 32 * ((rsa->key_size + 255) / 256);
>> i_len = o_len * 2;
>>
>> + sb_count = 0;
>> if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
>> /* sb_count is the number of storage block slots required
>> * for the modulus.
>> @@ -1852,7 +1853,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
>> *cmd_q, struct ccp_cmd *cmd)
>> ccp_dm_free(&exp);
>>
>> e_sb:
>> - if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
>> + if (sb_count)
>> cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key,
>> sb_count);
>>
>> return ret;
>>
>
> This is a fine solution. However, having lived with this annoyance for a
> while, and even hoping that a
> a later compiler fixes it, I would have preferred to either:
>
> 1) Initialize the local variable at declaration time, or

I try to never do that in general, see https://rusty.ozlabs.org/?p=232

> 2) Use this patch, which the compiler could optimize as it sees fit, and
> maintains a clear distinction
> for the code path for older devices:

This seems fine.

> @@ -1853,7 +1853,10 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
> *cmd_q, struct ccp_cmd *cmd)
>
> e_sb:
> if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
> + {
> + unsigned int sb_count = o_len / CCP_SB_BYTES;
> cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key,
> sb_count);
> + }

I would probably skip the local variable as well then, and just open-code the
length, unless that adds ugly line-wraps.

Arnd

2017-08-01 21:34:40

by Gary R Hook

[permalink] [raw]

Subject: Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

On 08/01/2017 03:35 PM, Arnd Bergmann wrote:
> On Tue, Aug 1, 2017 at 4:52 PM, Gary R Hook <[email protected]> wrote:
>> On 07/31/2017 03:49 PM, Arnd Bergmann wrote:
>>>
>>> The added support for version 5 CCPs introduced a false-positive
>>> warning in the RSA implementation:
>>>
>>> drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
>>> drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used
>>> uninitialized in this function [-Werror=maybe-uninitialized]
>>>
>>> This changes the code in a way that should make it easier for
>>> the compiler to track the state of the sb_count variable, and
>>> avoid the warning.
>>>
>>> Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5
>>> CCPs")
>>> Signed-off-by: Arnd Bergmann <[email protected]>
>>> ---
>>> drivers/crypto/ccp/ccp-ops.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
>>> index 40c062ad8726..a8bc207b099a 100644
>>> --- a/drivers/crypto/ccp/ccp-ops.c
>>> +++ b/drivers/crypto/ccp/ccp-ops.c
>>> @@ -1758,6 +1758,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
>>> *cmd_q, struct ccp_cmd *cmd)
>>> o_len = 32 * ((rsa->key_size + 255) / 256);
>>> i_len = o_len * 2;
>>>
>>> + sb_count = 0;
>>> if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
>>> /* sb_count is the number of storage block slots required
>>> * for the modulus.
>>> @@ -1852,7 +1853,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
>>> *cmd_q, struct ccp_cmd *cmd)
>>> ccp_dm_free(&exp);
>>>
>>> e_sb:
>>> - if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
>>> + if (sb_count)
>>> cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key,
>>> sb_count);
>>>
>>> return ret;
>>>
>>
>> This is a fine solution. However, having lived with this annoyance for a
>> while, and even hoping that a
>> a later compiler fixes it, I would have preferred to either:
>>
>> 1) Initialize the local variable at declaration time, or
>
> I try to never do that in general, see https://rusty.ozlabs.org/?p=232

I know. I just globally disagree with a global decision of this sort.
Now I make errors that are more complex, partially because I've shot myself
in the foot repeatedly, and learned from it.

Nonetheless...

I will ack your suggested patch. Thank you for addressing this. I've learned
something.

2017-08-01 21:38:04

by Gary R Hook

[permalink] [raw]

Subject: Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

2017-08-09 13:57:03

by Herbert Xu

[permalink] [raw]

Subject: Re: [PATCH] crypto: ccp - avoid uninitialized variable warning

On Mon, Jul 31, 2017 at 10:49:21PM +0200, Arnd Bergmann wrote:
> The added support for version 5 CCPs introduced a false-positive
> warning in the RSA implementation:
>
> drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
> drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> This changes the code in a way that should make it easier for
> the compiler to track the state of the sb_count variable, and
> avoid the warning.
>
> Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5 CCPs")
> Signed-off-by: Arnd Bergmann <[email protected]>

Patch applied. Thanks.
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt