Re: [PATCH 1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2017-11-24 06:17:31
Vaibhav Jain [off-list ref] writes:
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'.
.. and changes the calling convention of the function. Now it returns -ve error values, or a +ve TIDR value when it succeeds, or possibly 0 if that's returned by assign_thread_tidr(). Which I'm not sure you meant to do. If you did, you should at least document it. But frankly I'd rather we left it the way it was, -ve error or 0 for success. cheers
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index bfdd783e3916..a6eaf924c8b6 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c@@ -1569,19 +1569,21 @@ 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; - - mtspr(SPRN_TIDR, t->thread.tidr); + rc = assign_thread_tidr(); + if (rc > 0) { + t->thread.tidr = assign_thread_tidr(); + mtspr(SPRN_TIDR, t->thread.tidr); + } - return 0; + return rc; } #endif /* CONFIG_PPC64 */-- 2.14.3