[PATCH v3 2/3] powerpc/kprobes: 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 label 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>
---
Michael,
I have named the new label system_call_exit so as to follow the
existing labels (system_call and system_call_common) and to not
conflict with the syscall_exit private label.

- Naveen


 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 380361c0bb6a..e255221b0ec0 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)
@@ -388,7 +389,7 @@ 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)
-- 
2.12.2