[PATCH] powerpc/tm: Flush TM only if CPU has TM feature

[PATCH] powerpc/tm: Flush TM only if CPU has TM feature

[Gustavo Romero]

Commit cd63f3cf1d59 ("powerpc/tm: Fix saving of TM SPRs in core dump")
added code to access TM SPRs in flush_tmregs_to_thread(). However
flush_tmregs_to_thread() does not check if TM feature is available on
CPU before trying to access TM SPRs in order to copy live state to
thread structures. flush_tmregs_to_thread() is indeed guarded by
CONFIG_PPC_TRANSACTIONAL_MEM but it might be the case that kernel
was compiled with CONFIG_PPC_TRANSACTIONAL_MEM enabled and ran on
a CPU without TM feature available, thus rendering the execution
of TM instructions that are treated by the CPU as illegal instructions.

The fix is just to add proper checking in flush_tmregs_to_thread()
if CPU has the TM feature before accessing any TM-specific resource,
returning immediately if TM is no available on the CPU. Adding
that checking in flush_tmregs_to_thread() instead of in places
where it is called, like in vsr_get() and vsr_set(), is better because
avoids the same problem cropping up elsewhere.

Cc: stable@vger.kernel.org # v4.13+
Fixes: cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/ptrace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index 07cd22e..18f547f 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -124,6 +124,8 @@ static const struct pt_regs_offset regoffset_table[] = {
 static void flush_tmregs_to_thread(struct task_struct *tsk)
 {
 	/*
+	 * If CPU has no TM support, return.
+	 *
 	 * If task is not current, it will have been flushed already to
 	 * it's thread_struct during __switch_to().
 	 *
@@ -131,7 +133,7 @@ static void flush_tmregs_to_thread(struct task_struct *tsk)
 	 * in the appropriate thread structures from live.
 	 */
 
-	if (tsk != current)
+	if (!cpu_has_feature(CPU_FTR_TM) || tsk != current)
 		return;
 
 	if (MSR_TM_SUSPENDED(mfmsr())) {
-- 
2.7.4

[PATCH v2] powerpc/tm: Flush TM only if CPU has TM feature

[Gustavo Romero]

Commit cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
added code to access TM SPRs in flush_tmregs_to_thread(). However
flush_tmregs_to_thread() does not check if TM feature is available on
CPU before trying to access TM SPRs in order to copy live state to
thread structures. flush_tmregs_to_thread() is indeed guarded by
CONFIG_PPC_TRANSACTIONAL_MEM but it might be the case that kernel
was compiled with CONFIG_PPC_TRANSACTIONAL_MEM enabled and ran on
a CPU without TM feature available, thus rendering the execution
of TM instructions that are treated by the CPU as illegal instructions.

The fix is just to add proper checking in flush_tmregs_to_thread()
if CPU has the TM feature before accessing any TM-specific resource,
returning immediately if TM is no available on the CPU. Adding
that checking in flush_tmregs_to_thread() instead of in places
where it is called, like in vsr_get() and vsr_set(), is better because
avoids the same problem cropping up elsewhere.

Cc: stable@vger.kernel.org # v4.13+
Fixes: cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index 07cd22e..f52ad5b 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -131,7 +131,7 @@ static void flush_tmregs_to_thread(struct task_struct *tsk)
 	 * in the appropriate thread structures from live.
 	 */
 
-	if (tsk != current)
+	if ((!cpu_has_feature(CPU_FTR_TM)) || (tsk != current))
 		return;
 
 	if (MSR_TM_SUSPENDED(mfmsr())) {
-- 
2.7.4

Re: [PATCH v2] powerpc/tm: Flush TM only if CPU has TM feature

[Cyril Bur]

On Wed, 2017-09-13 at 22:13 -0400, Gustavo Romero wrote:
> Commit cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
> added code to access TM SPRs in flush_tmregs_to_thread(). However
> flush_tmregs_to_thread() does not check if TM feature is available on
> CPU before trying to access TM SPRs in order to copy live state to
> thread structures. flush_tmregs_to_thread() is indeed guarded by
> CONFIG_PPC_TRANSACTIONAL_MEM but it might be the case that kernel
> was compiled with CONFIG_PPC_TRANSACTIONAL_MEM enabled and ran on
> a CPU without TM feature available, thus rendering the execution
> of TM instructions that are treated by the CPU as illegal instructions.
> 
> The fix is just to add proper checking in flush_tmregs_to_thread()
> if CPU has the TM feature before accessing any TM-specific resource,
> returning immediately if TM is no available on the CPU. Adding
> that checking in flush_tmregs_to_thread() instead of in places
> where it is called, like in vsr_get() and vsr_set(), is better because
> avoids the same problem cropping up elsewhere.
> 
> Cc: stable@vger.kernel.org # v4.13+
> Fixes: cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
> Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com>

Keeping in mind I reviewed cd63f3c and feeling a bit sheepish having
missed this.

Reviewed-by: Cyril Bur <cyrilbur@gmail.com>

> ---
>  arch/powerpc/kernel/ptrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index 07cd22e..f52ad5b 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -131,7 +131,7 @@ static void flush_tmregs_to_thread(struct task_struct *tsk)
>  	 * in the appropriate thread structures from live.
>  	 */
>  
> -	if (tsk != current)
> +	if ((!cpu_has_feature(CPU_FTR_TM)) || (tsk != current))
>  		return;
>  
>  	if (MSR_TM_SUSPENDED(mfmsr())) {

Re: [v2] powerpc/tm: Flush TM only if CPU has TM feature

[Michael Ellerman]

On Thu, 2017-09-14 at 02:13:48 UTC, Gustavo Romero wrote:
> Commit cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
> added code to access TM SPRs in flush_tmregs_to_thread(). However
> flush_tmregs_to_thread() does not check if TM feature is available on
> CPU before trying to access TM SPRs in order to copy live state to
> thread structures. flush_tmregs_to_thread() is indeed guarded by
> CONFIG_PPC_TRANSACTIONAL_MEM but it might be the case that kernel
> was compiled with CONFIG_PPC_TRANSACTIONAL_MEM enabled and ran on
> a CPU without TM feature available, thus rendering the execution
> of TM instructions that are treated by the CPU as illegal instructions.
> 
> The fix is just to add proper checking in flush_tmregs_to_thread()
> if CPU has the TM feature before accessing any TM-specific resource,
> returning immediately if TM is no available on the CPU. Adding
> that checking in flush_tmregs_to_thread() instead of in places
> where it is called, like in vsr_get() and vsr_set(), is better because
> avoids the same problem cropping up elsewhere.
> 
> Cc: stable@vger.kernel.org # v4.13+
> Fixes: cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump")
> Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com>
> Reviewed-by: Cyril Bur <cyrilbur@gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/c1fa0768a8713b135848f78fd43ffc

cheers