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powerpc: Avoid signed to unsigned conversion in set_thread_tidr() 

There is an unsafe signed to unsigned conversion in set_thread_tidr()
that may cause an error value to be assigned to SPRN_TIDR register and
used as thread-id.

The issue happens as assign_thread_tidr() returns an int and
thread.tidr is an unsigned-long. So a negative error code returned
from assign_thread_tidr() will fail the error check and gets assigned
as tidr as a large positive value.

To fix this the patch assigns the return value of assign_thread_tidr()
to a temporary int and assigns it to thread.tidr iff its '> 0'.

The patch shouldn't impact the calling convention of set_thread_tidr()
i.e all -ve return-values are error codes and a return value of '0'
indicates success.

Fixes: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Reviewed-by: Christophe Lombard clombard@linux.vnet.ibm.com
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Vaibhav Jain 2017-11-28 08:23:04 +05:30 committed by Michael Ellerman
parent 2621e945fb
commit aca7573fde
1 changed files with 6 additions and 3 deletions
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9
arch/powerpc/kernel/process.c
View File

@ -1569,16 +1569,19 @@ void arch_release_task_struct(struct task_struct *t)
*/
int set_thread_tidr(struct task_struct *t)
{
int rc;
if (!cpu_has_feature(CPU_FTR_ARCH_300))
return -EINVAL;
if (t != current)
return -EINVAL;
t->thread.tidr = assign_thread_tidr();
if (t->thread.tidr < 0)
return t->thread.tidr;
rc = assign_thread_tidr();
if (rc < 0)
return rc;
t->thread.tidr = rc;
mtspr(SPRN_TIDR, t->thread.tidr);
return 0;