Commit aca7573f authored Nov 28, 2017 by Vaibhav Jain Committed by Michael Ellerman Nov 29, 2017

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: ec233ede("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>

parent 2621e945

arch/powerpc/kernel/process.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -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;