| Message ID | 20171124083338.15283-1-vaibhav@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2,1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr() | expand |
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 <vaibhav@linux.vnet.ibm.com> Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.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 */ >
Vaibhav Jain <vaibhav@linux.vnet.ibm.com> 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 <mpe@ellerman.id.au> writes: > Success == 0 > >> + return rc; > > Success == +ve TIDR > >> } > > 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.
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 */
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(-)