Re: [PATCH 10/12] powerpc/entry32: Blacklist exception entry points for kprobe.

From: Christophe Leroy
Date: Tue Mar 31 2020 - 01:51:47 EST




Le 30/03/2020 Ã 20:33, Christophe Leroy a ÃcritÂ:


Le 30/03/2020 Ã 19:08, Naveen N. Rao a ÃcritÂ:
Christophe Leroy wrote:
kprobe does not handle events happening in real mode.

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

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
Âarch/powerpc/kernel/entry_32.S | 7 +++++++
Â1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 94f78c03cb79..9a1a45d6038a 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -51,6 +51,7 @@ mcheck_transfer_to_handler:
ÂÂÂÂ mfsprÂÂÂ r0,SPRN_DSRR1
ÂÂÂÂ stwÂÂÂ r0,_DSRR1(r11)
ÂÂÂÂ /* fall through */
+_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler)

ÂÂÂÂ .globlÂÂÂ debug_transfer_to_handler
Âdebug_transfer_to_handler:
@@ -59,6 +60,7 @@ debug_transfer_to_handler:
ÂÂÂÂ mfsprÂÂÂ r0,SPRN_CSRR1
ÂÂÂÂ stwÂÂÂ r0,_CSRR1(r11)
ÂÂÂÂ /* fall through */
+_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler)

ÂÂÂÂ .globlÂÂÂ crit_transfer_to_handler
Âcrit_transfer_to_handler:
@@ -94,6 +96,7 @@ crit_transfer_to_handler:
ÂÂÂÂ rlwinmÂÂÂ r0,r1,0,0,(31 - THREAD_SHIFT)
ÂÂÂÂ stwÂÂÂ r0,KSP_LIMIT(r8)
ÂÂÂÂ /* fall through */
+_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
Â#endif

Â#ifdef CONFIG_40x
@@ -115,6 +118,7 @@ crit_transfer_to_handler:
ÂÂÂÂ rlwinmÂÂÂ r0,r1,0,0,(31 - THREAD_SHIFT)
ÂÂÂÂ stwÂÂÂ r0,KSP_LIMIT(r8)
ÂÂÂÂ /* fall through */
+_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
Â#endif

Â/*
@@ -127,6 +131,7 @@ crit_transfer_to_handler:
ÂÂÂÂ .globlÂÂÂ transfer_to_handler_full
Âtransfer_to_handler_full:
ÂÂÂÂ SAVE_NVGPRS(r11)
+_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full)
ÂÂÂÂ /* fall through */

ÂÂÂÂ .globlÂÂÂ transfer_to_handler
@@ -286,6 +291,8 @@ reenable_mmu:
ÂÂÂÂ lwzÂÂÂ r2, GPR2(r11)
ÂÂÂÂ bÂÂÂ fast_exception_return
Â#endif
+_ASM_NOKPROBE_SYMBOL(transfer_to_handler)
+_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont)

These are added after 'reenable_mmu', which is itself not blacklisted. Is that intentional?

Yes I put it as the complete end of the entry part, ie just before stack_ovf which is a function by itself.

Note that reenable_mmu is inside an #ifdef CONFIG_TRACE_IRQFLAGS.

I'm not completely sure where to put the _ASM_NOKPROBE_SYMBOL()s, that's the reason why I put it close to the symbol itself in my first series.

Could you have a look at the code and tell me what looks the most appropriate as a location to you ?

https://elixir.bootlin.com/linux/v5.6/source/arch/powerpc/kernel/entry_32.S#L230

Ok, thinking about it once more, I guess we have a problem as everything after that reenable_mmu will be visible.

So I'll respin

Christophe