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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH v2 10/12] powerpc/entry32: Blacklist exception entry points
 for kprobe.
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        naveen.n.rao@linux.vnet.ibm.com
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Tue, 31 Mar 2020 16:03:45 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

kprobe does not handle events happening in real mode.

As exception entry points are running with MMU disabled,
blacklist them.

The handling of TLF_NAPPING and TLF_SLEEPING is moved before the
CONFIG_TRACE_IRQFLAGS which contains 'reenable_mmu' because from there
kprobe will be possible as the kernel will run with MMU enabled.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
v2: Moved TLF_NAPPING and TLF_SLEEPING handling
---
 arch/powerpc/kernel/entry_32.S | 37 ++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 94f78c03cb79..215aa3a6d4f7 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -51,6 +51,7 @@ mcheck_transfer_to_handler:
 	mfspr	r0,SPRN_DSRR1
 	stw	r0,_DSRR1(r11)
 	/* fall through */
+_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler)
 
 	.globl	debug_transfer_to_handler
 debug_transfer_to_handler:
@@ -59,6 +60,7 @@ debug_transfer_to_handler:
 	mfspr	r0,SPRN_CSRR1
 	stw	r0,_CSRR1(r11)
 	/* fall through */
+_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler)
 
 	.globl	crit_transfer_to_handler
 crit_transfer_to_handler:
@@ -94,6 +96,7 @@ crit_transfer_to_handler:
 	rlwinm	r0,r1,0,0,(31 - THREAD_SHIFT)
 	stw	r0,KSP_LIMIT(r8)
 	/* fall through */
+_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
 #endif
 
 #ifdef CONFIG_40x
@@ -115,6 +118,7 @@ crit_transfer_to_handler:
 	rlwinm	r0,r1,0,0,(31 - THREAD_SHIFT)
 	stw	r0,KSP_LIMIT(r8)
 	/* fall through */
+_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
 #endif
 
 /*
@@ -127,6 +131,7 @@ crit_transfer_to_handler:
 	.globl	transfer_to_handler_full
 transfer_to_handler_full:
 	SAVE_NVGPRS(r11)
+_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full)
 	/* fall through */
 
 	.globl	transfer_to_handler
@@ -227,6 +232,23 @@ transfer_to_handler_cont:
 	SYNC
 	RFI				/* jump to handler, enable MMU */
 
+#if defined (CONFIG_PPC_BOOK3S_32) || defined(CONFIG_E500)
+4:	rlwinm	r12,r12,0,~_TLF_NAPPING
+	stw	r12,TI_LOCAL_FLAGS(r2)
+	b	power_save_ppc32_restore
+
+7:	rlwinm	r12,r12,0,~_TLF_SLEEPING
+	stw	r12,TI_LOCAL_FLAGS(r2)
+	lwz	r9,_MSR(r11)		/* if sleeping, clear MSR.EE */
+	rlwinm	r9,r9,0,~MSR_EE
+	lwz	r12,_LINK(r11)		/* and return to address in LR */
+	kuap_restore r11, r2, r3, r4, r5
+	lwz	r2, GPR2(r11)
+	b	fast_exception_return
+#endif
+_ASM_NOKPROBE_SYMBOL(transfer_to_handler)
+_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont)
+
 #ifdef CONFIG_TRACE_IRQFLAGS
 1:	/* MSR is changing, re-enable MMU so we can notify lockdep. We need to
 	 * keep interrupts disabled at this point otherwise we might risk
@@ -272,21 +294,6 @@ reenable_mmu:
 	bctr				/* jump to handler */
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
-#if defined (CONFIG_PPC_BOOK3S_32) || defined(CONFIG_E500)
-4:	rlwinm	r12,r12,0,~_TLF_NAPPING
-	stw	r12,TI_LOCAL_FLAGS(r2)
-	b	power_save_ppc32_restore
-
-7:	rlwinm	r12,r12,0,~_TLF_SLEEPING
-	stw	r12,TI_LOCAL_FLAGS(r2)
-	lwz	r9,_MSR(r11)		/* if sleeping, clear MSR.EE */
-	rlwinm	r9,r9,0,~MSR_EE
-	lwz	r12,_LINK(r11)		/* and return to address in LR */
-	kuap_restore r11, r2, r3, r4, r5
-	lwz	r2, GPR2(r11)
-	b	fast_exception_return
-#endif
-
 #ifndef CONFIG_VMAP_STACK
 /*
  * On kernel stack overflow, load up an initial stack pointer
-- 
2.25.0