* [PATCH v3] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()
@ 2017-11-27 17:19 Vaibhav Jain
2017-11-27 23:41 ` Sukadev Bhattiprolu
0 siblings, 1 reply; 3+ messages in thread
From: Vaibhav Jain @ 2017-11-27 17:19 UTC (permalink / raw)
To: linuxppc-dev, Sukadev Bhattiprolu, Christophe Lombard,
Philippe Bergheaud, Michael Ellerman
Cc: Vaibhav Jain, Frederic Barrat, Andrew Donnellan, Alastair D'Silva
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: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
---
Changelog:
v3 -> Updated the patch to not impact the calling convention [Mpe, Christophe]
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 | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index bfdd783e3916..9fb69211a3d4 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1569,19 +1569,22 @@ 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);
-
- return 0;
+ rc = assign_thread_tidr();
+ if (rc > 0) {
+ t->thread.tidr = rc;
+ mtspr(SPRN_TIDR, t->thread.tidr);
+ return 0;
+ } else {
+ return rc;
+ }
}
#endif /* CONFIG_PPC64 */
--
2.14.3
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v3] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()
2017-11-27 17:19 [PATCH v3] powerpc: Avoid signed to unsigned conversion in set_thread_tidr() Vaibhav Jain
@ 2017-11-27 23:41 ` Sukadev Bhattiprolu
2017-11-28 2:57 ` Vaibhav Jain
0 siblings, 1 reply; 3+ messages in thread
From: Sukadev Bhattiprolu @ 2017-11-27 23:41 UTC (permalink / raw)
To: Vaibhav Jain
Cc: linuxppc-dev, Christophe Lombard, Philippe Bergheaud,
Michael Ellerman, Frederic Barrat, Andrew Donnellan,
Alastair D'Silva
Vaibhav Jain [vaibhav@linux.vnet.ibm.com] 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.
Thanks for fixing this. I have a comment below
>
> 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: ec233ede4c86("powerpc: Add support for setting SPRN_TIDR")
> Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
>
> ---
> Changelog:
>
> v3 -> Updated the patch to not impact the calling convention [Mpe, Christophe]
>
> 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 | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index bfdd783e3916..9fb69211a3d4 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1569,19 +1569,22 @@ 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);
> -
> - return 0;
> + rc = assign_thread_tidr();
> + if (rc > 0) {
> + t->thread.tidr = rc;
> + mtspr(SPRN_TIDR, t->thread.tidr);
> + return 0;
> + } else {
> + return rc;
> + }
We can eliminate the 'else' and be consistent with existing code, if
we check for error (i.e rc < 0) and return rc. assign_thread_tidr() will
not return 0, but even if it did, setting the register and thread.tidr
to 0 should not be a problem.
Sukadev
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v3] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()
2017-11-27 23:41 ` Sukadev Bhattiprolu
@ 2017-11-28 2:57 ` Vaibhav Jain
0 siblings, 0 replies; 3+ messages in thread
From: Vaibhav Jain @ 2017-11-28 2:57 UTC (permalink / raw)
To: Sukadev Bhattiprolu
Cc: Philippe Bergheaud, Frederic Barrat, Alastair D'Silva,
Andrew Donnellan, linuxppc-dev, Christophe Lombard
Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:
> We can eliminate the 'else' and be consistent with existing code, if
> we check for error (i.e rc < 0) and return rc. assign_thread_tidr() will
> not return 0, but even if it did, setting the register and thread.tidr
> to 0 should not be a problem.
Thanks for the suggestion Sukadev. I have sent out a v4 at
http://patchwork.ozlabs.org/patch/841937/ with the update.
--
Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-11-27 17:19 [PATCH v3] powerpc: Avoid signed to unsigned conversion in set_thread_tidr() Vaibhav Jain
2017-11-27 23:41 ` Sukadev Bhattiprolu
2017-11-28 2:57 ` Vaibhav Jain
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