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

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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 <arnd@xxxxxxxx>
---
 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;
 }


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