Re: [PATCH v2 1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()
From: Andrew Donnellan <hidden>
Date: 2017-11-27 01:00:48
On 24/11/17 19:33, Vaibhav Jain wrote:
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, +ve return values are
assigned Thread-ids. The way function is implemented it should never
return a '0'.
Fixes: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
Signed-off-by: Vaibhav Jain <redacted>Reviewed-by: Andrew Donnellan <redacted>
quoted hunk ↗ jump to hunk
--- Changelog: v2 -> * Update the patch description to document the calling convention of set_thread_tidr(). [Mpe] * Fix a tidr allocation leak. --- arch/powerpc/kernel/process.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index bfdd783e3916..5d8176c7c2d8 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 = rc; + mtspr(SPRN_TIDR, t->thread.tidr); + } - return 0; + return rc; } #endif /* CONFIG_PPC64 */
-- Andrew Donnellan OzLabs, ADL Canberra andrew.donnellan@au1.ibm.com IBM Australia Limited