powerpc/tm: Limit TM code inside PPC_TRANSACTIONAL_MEM

[ Upstream commit 897bc3df8c5aebb54c32d831f917592e873d0559 ]

Commit e1c3743e1a20 ("powerpc/tm: Set MSR[TS] just prior to recheckpoint")
moved a code block around and this block uses a 'msr' variable outside of
the CONFIG_PPC_TRANSACTIONAL_MEM, however the 'msr' variable is declared
inside a CONFIG_PPC_TRANSACTIONAL_MEM block, causing a possible error when
CONFIG_PPC_TRANSACTION_MEM is not defined.

	error: 'msr' undeclared (first use in this function)

This is not causing a compilation error in the mainline kernel, because
'msr' is being used as an argument of MSR_TM_ACTIVE(), which is defined as
the following when CONFIG_PPC_TRANSACTIONAL_MEM is *not* set:

	#define MSR_TM_ACTIVE(x) 0

This patch just fixes this issue avoiding the 'msr' variable usage outside
the CONFIG_PPC_TRANSACTIONAL_MEM block, avoiding trusting in the
MSR_TM_ACTIVE() definition.

Cc: stable@vger.kernel.org
Reported-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Fixes: e1c3743e1a20 ("powerpc/tm: Set MSR[TS] just prior to recheckpoint")
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 979b9463e17bc7e7f4c74e4737eb9bb560285e43..927384d85fafb2531ad248bedf3701df49f0f1cd 100644 (file)
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -746,12 +746,25 @@ int sys_rt_sigreturn(unsigned long r3, unsigned long r4, unsigned long r5,
                if (restore_tm_sigcontexts(current, &uc->uc_mcontext,
                                           &uc_transact->uc_mcontext))
                        goto badframe;
-       }
-       else
-       /* Fall through, for non-TM restore */
+       } else
 #endif
-       if (restore_sigcontext(current, NULL, 1, &uc->uc_mcontext))
-               goto badframe;
+       {
+               /*
+                * Fall through, for non-TM restore
+                *
+                * Unset MSR[TS] on the thread regs since MSR from user
+                * context does not have MSR active, and recheckpoint was
+                * not called since restore_tm_sigcontexts() was not called
+                * also.
+                *
+                * If not unsetting it, the code can RFID to userspace with
+                * MSR[TS] set, but without CPU in the proper state,
+                * causing a TM bad thing.
+                */
+               current->thread.regs->msr &= ~MSR_TS_MASK;
+               if (restore_sigcontext(current, NULL, 1, &uc->uc_mcontext))
+                       goto badframe;
+       }
 
        if (restore_altstack(&uc->uc_stack))
                goto badframe;