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* [PATCH v2 1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()
@ 2017-11-24  8:33 Vaibhav Jain
  2017-11-24  8:33 ` [PATCH v2 2/2] powerpc: Do not assign thread.tidr if already assigned Vaibhav Jain
                   ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Vaibhav Jain @ 2017-11-24  8:33 UTC (permalink / raw)
  To: linuxppc-dev, Sukadev Bhattiprolu, Christophe Lombard,
	Philippe Bergheaud, Michael Ellerman
  Cc: Vaibhav Jain, Andrew Donnellan, Alastair D'Silva, Frederic Barrat

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 <vaibhav@linux.vnet.ibm.com>

---
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 */
-- 
2.14.3

^ permalink raw reply related	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2017-11-29 12:06 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-11-24  8:33 [PATCH v2 1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr() Vaibhav Jain
2017-11-24  8:33 ` [PATCH v2 2/2] powerpc: Do not assign thread.tidr if already assigned Vaibhav Jain
2017-11-27  1:06   ` Andrew Donnellan
2017-11-29 12:06   ` [v2,2/2] " Michael Ellerman
2017-11-27  1:00 ` [PATCH v2 1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr() Andrew Donnellan
2017-11-27  3:48 ` Michael Ellerman
2017-11-27 17:24   ` Vaibhav Jain

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