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 0x0000e268
> [ 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: 00001032 <ME,IR,DR,RI> CR: 2a4d3c52 XER: 00000000
> [ 33.150699] DAR: 0000e268 DSISR: c0000000
> [ 33.150699] GPR00: c000b09c ca4d3c10 c66d0620 00000000 ca4d3c60 00000000 00009032 00000000
> [ 33.150699] GPR08: 00020000 00000000 c087de44 c000afe0 c66d0ad0 100d3dd6 fffffff3 00000000
> [ 33.150699] GPR16: 00000000 00000041 00000000 ca4d3d70 00000000 00000000 0000416d 00000000
> [ 33.150699] GPR24: 00000004 c53b6128 00000000 0000e268 00000000 c07c0000 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 81220000 38600001 3929ffff 91220000 80010024 bb410008 7c0803a6
> [ 33.280992] 38210020 4e800020 38600000 4e800020 <813b0000> 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 <[email protected]>
> Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
> Cc: [email protected]
> Cc: Naveen N. Rao <[email protected]>
> Cc: Masami Hiramatsu <[email protected]>
> Signed-off-by: Christophe Leroy <[email protected]>
>
> ---
> 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 <[email protected]>
> ---
> 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
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
>> 0x0000e268
>> [ 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: 00001032 <ME,IR,DR,RI> CR: 2a4d3c52 XER: 00000000
>> [ 33.150699] DAR: 0000e268 DSISR: c0000000
>> [ 33.150699] GPR00: c000b09c ca4d3c10 c66d0620 00000000 ca4d3c60
>> 00000000 00009032 00000000
>> [ 33.150699] GPR08: 00020000 00000000 c087de44 c000afe0 c66d0ad0
>> 100d3dd6 fffffff3 00000000
>> [ 33.150699] GPR16: 00000000 00000041 00000000 ca4d3d70 00000000
>> 00000000 0000416d 00000000
>> [ 33.150699] GPR24: 00000004 c53b6128 00000000 0000e268 00000000
>> c07c0000 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 81220000 38600001 3929ffff 91220000 80010024
>> bb410008 7c0803a6
>> [ 33.280992] 38210020 4e800020 38600000 4e800020 <813b0000> 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 <[email protected]>
>> Fixes: 6cc89bad60a6 ("powerpc/kprobes: Invoke handlers directly")
>> Cc: [email protected]
>> Cc: Naveen N. Rao <[email protected]>
>> Cc: Masami Hiramatsu <[email protected]>
>> Signed-off-by: Christophe Leroy <[email protected]>
>>
>> ---
>> 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 <[email protected]>
>> ---
>> 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