Re: [PATCH v2] powerpc/kprobes: Fix trap address when trap happened in real mode

2020-02-18 Thread Christophe Leroy 




Le 18/02/2020 à 15:55, Naveen N. Rao a écrit :

Christophe Leroy wrote:

When a program check exception happens while MMU translation is
disabled, following Oops happens in kprobe_handler() in the following
code:

    } else if (*addr != BREAKPOINT_INSTRUCTION) {

[   33.098554] BUG: Unable to handle kernel data access on read at 
0xe268

[   33.105091] Faulting instruction address: 0xc000ec34
[   33.110010] Oops: Kernel access of bad area, sig: 11 [#1]
[   33.115348] BE PAGE_SIZE=16K PREEMPT CMPC885
[   33.119540] Modules linked in:
[   33.122591] CPU: 0 PID: 429 Comm: cat Not tainted 
5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267

[   33.131005] NIP:  c000ec34 LR: c000ecd8 CTR: c019cab8
[   33.136002] REGS: ca4d3b58 TRAP: 0300   Not tainted  
(5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)

[   33.144324] MSR:  1032   CR: 2a4d3c52  XER: 
[   33.150699] DAR: e268 DSISR: c000
[   33.150699] GPR00: c000b09c ca4d3c10 c66d0620  ca4d3c60 
 9032 
[   33.150699] GPR08: 0002  c087de44 c000afe0 c66d0ad0 
100d3dd6 fff3 
[   33.150699] GPR16:  0041  ca4d3d70  
 416d 
[   33.150699] GPR24: 0004 c53b6128  e268  
c07c c07bb6fc ca4d3c60

[   33.188015] NIP [c000ec34] kprobe_handler+0x128/0x290
[   33.192989] LR [c000ecd8] kprobe_handler+0x1cc/0x290
[   33.197854] Call Trace:
[   33.200340] [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
[   33.206590] [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
[   33.212392] --- interrupt: 700 at 0xe268
[   33.270401] Instruction dump:
[   33.273335] 913e0008 8122 3861 3929 9122 80010024 
bb410008 7c0803a6
[   33.280992] 38210020 4e800020 3860 4e800020 <813b> 6d2a7fe0 
2f8a0008 419e0154

[   33.288841] ---[ end trace 5b9152d4cdadd06d ]---

kprobe is not prepared to handle events in real mode and functions
running in real mode should have been blacklisted, so kprobe_handler()
can safely bail out telling 'this trap is not mine' for any trap that
happened while in real-mode.

If the trap happened with MSR_IR cleared, return 0 immediately.

Reported-by: Larry Finger 
Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
Cc: sta...@vger.kernel.org
Cc: Naveen N. Rao 
Cc: Masami Hiramatsu 
Signed-off-by: Christophe Leroy 

---
v2: bailing out instead of converting real-time address to virtual and 
continuing.


The bug might have existed even before that commit from Naveen.

Signed-off-by: Christophe Leroy 
---
 arch/powerpc/kernel/kprobes.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/kprobes.c 
b/arch/powerpc/kernel/kprobes.c

index 2d27ec4feee4..673f349662e8 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
 if (user_mode(regs))
 return 0;

+    if (!(regs->msr & MSR_IR))
+    return 0;
+


Should we also check for MSR_DR? Are there scenarios with ppc32 where 
MSR_IR is on, but MSR_DR is off?


Yes indeed.

Christophe

Re: [PATCH v2] powerpc/kprobes: Fix trap address when trap happened in real mode

2020-02-18 Thread Naveen N. Rao 

Christophe Leroy wrote:

When a program check exception happens while MMU translation is
disabled, following Oops happens in kprobe_handler() in the following
code:

} else if (*addr != BREAKPOINT_INSTRUCTION) {

[   33.098554] BUG: Unable to handle kernel data access on read at 0xe268
[   33.105091] Faulting instruction address: 0xc000ec34
[   33.110010] Oops: Kernel access of bad area, sig: 11 [#1]
[   33.115348] BE PAGE_SIZE=16K PREEMPT CMPC885
[   33.119540] Modules linked in:
[   33.122591] CPU: 0 PID: 429 Comm: cat Not tainted 
5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267
[   33.131005] NIP:  c000ec34 LR: c000ecd8 CTR: c019cab8
[   33.136002] REGS: ca4d3b58 TRAP: 0300   Not tainted  
(5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)
[   33.144324] MSR:  1032   CR: 2a4d3c52  XER: 
[   33.150699] DAR: e268 DSISR: c000
[   33.150699] GPR00: c000b09c ca4d3c10 c66d0620  ca4d3c60  
9032 
[   33.150699] GPR08: 0002  c087de44 c000afe0 c66d0ad0 100d3dd6 
fff3 
[   33.150699] GPR16:  0041  ca4d3d70   
416d 
[   33.150699] GPR24: 0004 c53b6128  e268  c07c 
c07bb6fc ca4d3c60
[   33.188015] NIP [c000ec34] kprobe_handler+0x128/0x290
[   33.192989] LR [c000ecd8] kprobe_handler+0x1cc/0x290
[   33.197854] Call Trace:
[   33.200340] [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
[   33.206590] [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
[   33.212392] --- interrupt: 700 at 0xe268
[   33.270401] Instruction dump:
[   33.273335] 913e0008 8122 3861 3929 9122 80010024 bb410008 
7c0803a6
[   33.280992] 38210020 4e800020 3860 4e800020 <813b> 6d2a7fe0 2f8a0008 
419e0154
[   33.288841] ---[ end trace 5b9152d4cdadd06d ]---

kprobe is not prepared to handle events in real mode and functions
running in real mode should have been blacklisted, so kprobe_handler()
can safely bail out telling 'this trap is not mine' for any trap that
happened while in real-mode.

If the trap happened with MSR_IR cleared, return 0 immediately.

Reported-by: Larry Finger 
Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
Cc: sta...@vger.kernel.org
Cc: Naveen N. Rao 
Cc: Masami Hiramatsu 
Signed-off-by: Christophe Leroy 

---
v2: bailing out instead of converting real-time address to virtual and 
continuing.

The bug might have existed even before that commit from Naveen.

Signed-off-by: Christophe Leroy 
---
 arch/powerpc/kernel/kprobes.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 2d27ec4feee4..673f349662e8 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
if (user_mode(regs))
return 0;

+   if (!(regs->msr & MSR_IR))
+   return 0;
+


Should we also check for MSR_DR? Are there scenarios with ppc32 where 
MSR_IR is on, but MSR_DR is off?



- Naveen

[PATCH v2] powerpc/kprobes: Fix trap address when trap happened in real mode

2020-02-18 Thread Christophe Leroy 
When a program check exception happens while MMU translation is
disabled, following Oops happens in kprobe_handler() in the following
code:

} else if (*addr != BREAKPOINT_INSTRUCTION) {

[   33.098554] BUG: Unable to handle kernel data access on read at 0xe268
[   33.105091] Faulting instruction address: 0xc000ec34
[   33.110010] Oops: Kernel access of bad area, sig: 11 [#1]
[   33.115348] BE PAGE_SIZE=16K PREEMPT CMPC885
[   33.119540] Modules linked in:
[   33.122591] CPU: 0 PID: 429 Comm: cat Not tainted 
5.6.0-rc1-s3k-dev-00824-g84195dc6c58a #3267
[   33.131005] NIP:  c000ec34 LR: c000ecd8 CTR: c019cab8
[   33.136002] REGS: ca4d3b58 TRAP: 0300   Not tainted  
(5.6.0-rc1-s3k-dev-00824-g84195dc6c58a)
[   33.144324] MSR:  1032   CR: 2a4d3c52  XER: 
[   33.150699] DAR: e268 DSISR: c000
[   33.150699] GPR00: c000b09c ca4d3c10 c66d0620  ca4d3c60  
9032 
[   33.150699] GPR08: 0002  c087de44 c000afe0 c66d0ad0 100d3dd6 
fff3 
[   33.150699] GPR16:  0041  ca4d3d70   
416d 
[   33.150699] GPR24: 0004 c53b6128  e268  c07c 
c07bb6fc ca4d3c60
[   33.188015] NIP [c000ec34] kprobe_handler+0x128/0x290
[   33.192989] LR [c000ecd8] kprobe_handler+0x1cc/0x290
[   33.197854] Call Trace:
[   33.200340] [ca4d3c30] [c000b09c] program_check_exception+0xbc/0x6fc
[   33.206590] [ca4d3c50] [c000e43c] ret_from_except_full+0x0/0x4
[   33.212392] --- interrupt: 700 at 0xe268
[   33.270401] Instruction dump:
[   33.273335] 913e0008 8122 3861 3929 9122 80010024 bb410008 
7c0803a6
[   33.280992] 38210020 4e800020 3860 4e800020 <813b> 6d2a7fe0 2f8a0008 
419e0154
[   33.288841] ---[ end trace 5b9152d4cdadd06d ]---

kprobe is not prepared to handle events in real mode and functions
running in real mode should have been blacklisted, so kprobe_handler()
can safely bail out telling 'this trap is not mine' for any trap that
happened while in real-mode.

If the trap happened with MSR_IR cleared, return 0 immediately.

Reported-by: Larry Finger 
Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
Cc: sta...@vger.kernel.org
Cc: Naveen N. Rao 
Cc: Masami Hiramatsu 
Signed-off-by: Christophe Leroy 

---
v2: bailing out instead of converting real-time address to virtual and 
continuing.

The bug might have existed even before that commit from Naveen.

Signed-off-by: Christophe Leroy 
---
 arch/powerpc/kernel/kprobes.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 2d27ec4feee4..673f349662e8 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -264,6 +264,9 @@ int kprobe_handler(struct pt_regs *regs)
if (user_mode(regs))
return 0;
 
+   if (!(regs->msr & MSR_IR))
+   return 0;
+
/*
 * We don't want to be preempted for the entire
 * duration of kprobe processing
-- 
2.25.0