[PATCH v3 4/6] powerpc/64s: Un-blacklist system_call() from kprobes

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

It is actually safe to probe system_call() in entry_64.S, but only till
we unset MSR_RI. To allow this, add a new symbol system_call_exit()
after the mtmsrd and blacklist that. Though the mtmsrd instruction
itself is now whitelisted, we won't be allowed to probe on it as we
don't allow probing on rfi and mtmsr instructions (checked for in
arch_prepare_kprobe()).

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/entry_64.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index ef8e6615b8ba..feeeadc9aa71 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -204,6 +204,7 @@ system_call:			/* label this so stack traces look sane */
 	mtmsrd	r11,1
 #endif /* CONFIG_PPC_BOOK3E */
 
+system_call_exit:
 	ld	r9,TI_FLAGS(r12)
 	li	r11,-MAX_ERRNO
 	andi.	r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
@@ -412,7 +413,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	b	.	/* prevent speculative execution */
 #endif
 _ASM_NOKPROBE_SYMBOL(system_call_common);
-_ASM_NOKPROBE_SYMBOL(system_call);
+_ASM_NOKPROBE_SYMBOL(system_call_exit);
 
 /* Save non-volatile GPRs, if not already saved. */
 _GLOBAL(save_nvgprs)
-- 
2.13.1