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

[Naveen N. Rao]

Christophe Leroy wrote:


Le 30/03/2020 à 20:33, Christophe Leroy a écrit :


Le 30/03/2020 à 19:08, Naveen N. Rao a écrit :
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.le...@c-s.fr>
---
 arch/powerpc/kernel/entry_32.S | 7 +++++++
 1 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:
     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
@@ -286,6 +291,8 @@ reenable_mmu:
     lwz    r2, GPR2(r11)
     b    fast_exception_return
 #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.

I see that we reach reenable_mmu through a 'rfi' with MSR_KERNEL, which 
seems safe to me. So, I figured it can be probed without issues?

- Naveen