[PATCH v2 1/2] 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, +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>

---
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

If set_thread_tidr() is called twice for same task_struct then it will
allocate a new tidr value to it leaving the previous value still
dangling in the vas_thread_ida table.

To fix this the patch changes set_thread_tidr() to check if a tidr
value is already assigned to the task_struct and if yes then returns
the existing value from function instead of allocating a new one.

Fixes: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
Signed-off-by: Vaibhav Jain <redacted>
---
v2 ->	Fix minor spell errors in patch description
---
 arch/powerpc/kernel/process.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 5d8176c7c2d8..9a72282b022d 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c

@@ -1577,6 +1577,9 @@ int set_thread_tidr(struct task_struct *t)
 	if (t != current)
 		return -EINVAL;
 
+	if (t->thread.tidr)
+		return t->thread.tidr;
+
 	rc = assign_thread_tidr();
 	if (rc > 0) {
 		t->thread.tidr = rc;

-- 
2.14.3

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>

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan@au1.ibm.com  IBM Australia Limited

On 24/11/17 19:33, Vaibhav Jain wrote:

If set_thread_tidr() is called twice for same task_struct then it will
allocate a new tidr value to it leaving the previous value still
dangling in the vas_thread_ida table.

To fix this the patch changes set_thread_tidr() to check if a tidr
value is already assigned to the task_struct and if yes then returns
the existing value from function instead of allocating a new one.

Fixes: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
Signed-off-by: Vaibhav Jain <redacted>

Reviewed-by: Andrew Donnellan <redacted>

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan@au1.ibm.com  IBM Australia Limited

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'.

The patch shouldn't impact the calling convention of set_thread_tidr()

But it does? I'm really confused.

Please fix and resend.

cheers

 int set_thread_tidr(struct task_struct *t)
 {
+	int rc;
+
 	if (!cpu_has_feature(CPU_FTR_ARCH_300))
 		return -EINVAL;

                ^
                -ve error

 
 	if (t != current)
 		return -EINVAL;

                ^
                -ve error

 
-	t->thread.tidr = assign_thread_tidr();
-	if (t->thread.tidr < 0)
-		return t->thread.tidr;

                ^
                -ve error

Yes I know we never hit that case because of the bug, that is what this
patch should be fixing, and only that.

-
-	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;

Success == 0

+	return rc;

Success == +ve TIDR

 }

cheers

Michael Ellerman [off-list ref] writes:

Success == 0

quoted

+	return rc;

Success == +ve TIDR

quoted

 }

cheers

Thanks for reviewing the patch Mpe, I have updated the patch and sent a
v3 with the fix that shouldn't impact the calling convention.

-- 
Vaibhav Jain [off-list ref]
Linux Technology Center, IBM India Pvt. Ltd.

On Fri, 2017-11-24 at 08:33:38 UTC, Vaibhav Jain wrote:

If set_thread_tidr() is called twice for same task_struct then it will
allocate a new tidr value to it leaving the previous value still
dangling in the vas_thread_ida table.

To fix this the patch changes set_thread_tidr() to check if a tidr
value is already assigned to the task_struct and if yes then returns
the existing value from function instead of allocating a new one.

Fixes: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
Signed-off-by: Vaibhav Jain <redacted>
Reviewed-by: Andrew Donnellan <redacted>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/7e4d4233260be0611c7fbdb2730c12

cheers